plant pathology final exam
who conducted the experiment that set the stage for Germ Theory, and what was the experiment?
Anton de Bary (father of modern plant pathology) conducted an experiment where two groups of potatoes were placed in the same cool, moist environmental conditions but one was infected with fungal spores from P. infestans.
T/F: historically fungal taxonomy was based on phylogenetic relationships derived from DNA sequence information
False - historically fungal taxonomy was based primarily on reproductive structures
T/F: downey mildew is a facultative parasite
False - it is an obligate parasite and a biotroph
T/F: oak wilt is most common in bur oaks
False - it is most common in red oak but may cause damage to other oaks
T/F: crown gall infects both monocots and dicots
False - it only infects dicots, NEVER monocots
T/F: in 1917, state and federal authorities began an eradication program for citrus canker in Florida that required people to pay a fine for unreported infections
False - it was 1915
T/F: moisture level does not effect root diseases
False - moisture level (too high or too low) may stress the host
T/F: new fungal taxonomy based primarily on reproductive structures
False - new fungal taxonomy is based on phylogenetic relationships
T/F: cyst nematodes feeding induces mitosis and DNA replication creating giant cells
False - root-knot nematodes do this
T/F: asexual spores have increased survival in cold climates
False - sexual spores are tolerant of adverse conditions
T/F: the Siberian elm is the most seriously affected by DED
False - the American elm is the most affected, the Siberian elm is tolerant
T/F: chestnut blight is not an example of new encounter disease
False - the fungus was introduced from Asia to New York and it destroyed native chestnut populations in US over 40 years
T/F: there are some highly resistant varieties of pear that can be planted to combat fire blight
False - there are no highly resistant varieties, but there are some that are less susceptible.
T/F: almost all plant bacterial pathogens are spherical
False - they are rod shaped (bacilli)
T/F: bacteria are multicellular
False - they are unicellular and sometimes form colonies
T/F: Cryphonectria parasitica reproduces sexually with an apothecium
False - they contain a perithecium that contain many asci with 8 ascospores each
T/F: necrotrophs are species specific, meaning they only infect a few types of plants
False - they do not care about species and have a wide range of hosts
T/F: fungi prefer dry habitats
False - they need moist habitats!
T/F: Chytridiomycetes produce zoospores with multiple flagella
False - they produce zoospores with a single flagella
T/F: bacteria penetrate host plants directly
False - they rely on wounds or natural openings
T/F: sexual reproduction relies on meiosis while asexual reproduction relies on mitosis
True
T/F: some pathogens physically pierce plant tissues or use enzymes to digest cell walls
True
T/F: sometimes for penetration to occur, highly specialized structures such as a germ tube or appressorium must form
True
T/F: systemic symptoms refer to symptoms that develop throughout the plants and are the result of systemic invasion
True
T/F: there are different types of directional fungal growth called tropisms
True
T/F: there are no regions that coffee rust is not currently present today
True
T/F: vegetative hyphae can be haploid, diploid, or dikaryotic
True
T/F: viruses are becoming increasingly important target for disease resistance
True
T/F: viruses rely completely on wounds for penetration
True
T/F: zoospores (asexual) are produced in zoosporangium and oospore (sexual) are in oogonium
True
T/F: different propagules have different growth requirements
True - all pathogens in their vegetative state are capable of initiating infection, but spores require specific conditions for growth.
T/F: Ascomycetes is known as the "Sac Fungi" after their ascus that produces ascospores
True - ascus means "SAC" in latin
T/F: a spore bearing structure is called a sporophore
True - example: conidium on conidiophore
T/F: Phytophthora is heterothallic
True - female and male organs are on different strains
T/F: pathogens can survive dormant in seeds
True - that's why seeds are coated with fungicide
T/F: Dutch elm disease is heterothallic
True - they need two mating types for sexual reproduction
T/F: fungus have specialized structures for penetration
True - they use appressoria and penetration pegs
who first proposed germ theory?
Prevost in 1807 when he repeated Tillet's experiments and proposed that the cause for diseases are microscopic fungal spores that lead to infection and that the reduction of smut after seed treatment with copper sulfate results from inhibition of spore germination
T/F: chestnut blight is an example of new encounter disease
True. American chestnut is native to the Appalachians, and the pathogen was introduced from Asia.
what pathogen causes apple scab?
Venturia inaequalis
what are two barriers for the proof that bacteria cause plant disease?
1. routine culture of bacteria- Robert Koch 2. high quality light microscopes - Thomas Burrill
what are some examples of biotrophic pathogens?
1. rust 2. downy mildew 3. powdery mildew
how is TMV controlled?
1. sanitation 2. crop rotation 3. host resistance 4. protection - cross protection and MILK
what did Tillet do in 1755?
he found that he could increase smut on wheat plants if he added smut dust to the seeds and that he could reduce it if he added copper sulfate to the seeds
how did Harold Flor develop the gene-for-gene concept in plant pathogen interactions?
he was working on flax rust called Melampsora lini (autoecious biotrophic diploid rust with a single host), he had varieties of the host flax that were resistant to some races of the pathogens and susceptible to others
what is the difference between hemiparasitic plants and holoparasitic plants?
hemi or semiparasitic plants have photosynthetic leaves but may lack roots, holoparasitic plants do not have roots nor can they photosynthesize, making them entirely dependent on their host.
cellulose vs. hemicellulose
hemicellulose has 500-3000 sugar units compared to 7000-15000 glucose molecules per polymer for cellulose - they form a major portion of the cell wall and middle lamella
what is Erwina amylovora?
important plant pathogenic bacteria that causes fire blight of pear
what is the effect of ice nucleation-active bacteria and what are some examples?
infected plants become sensitive to frost damage as ice forms inside of their cells. examples: P. syringae, P. fluorescens, and Pantoea herbicola
what is necrosis?
infection of the entire plant that leads to death
how does low temperature affect plant growth?
more damage, freeze damage results in disruption of plasma membrane, sweetening of potato, and frost damage
what is a canker?
a sunken lesion on the branch, trunk, or stem of a plant. phloem is killed and translocation of nutrients is cut off. toxins are produced that diffuse into the xylem and the plant reacts by producing gums and blocks water transport, causing wilt.
what are the symptoms of citrus canker?
a leaf-spotting and fruit-blemishing disease, but when conditions are highly favorable for infection it causes defoliation, shoot dieback, and fruit drop
what is damping-off disease?
a seedling disease that affects roots and plant parts that are in contact with the soil. pre-emergence and post-emergence damping off. severely limits growth and productivity.
what is the parasexual cycle?
a sequence involving heterokaryon formation, diploidization, and haploidization, often resulting in the formation of recombinant nuclei - it can occur at any point or continuously throughout the lifecycle
what is a virus?
a set of genes that replicate inside of the host cell
what is the structure of a virus?
a single strand of RNA surrounded by a protein sheath, some can be double stranded DNA or RNA
what is Pythium spp.?
an oomycete that causes damping off disease of seedlings - this is a necrotroph
what are downy mildews?
an oomycete that is an obligate parasite and can be cause by several different genera - this is a biotroph
which of the following is not a characteristic of fungus? a. usually filamentous b. most are microscopic c. they have chlorophyll d. they are branched e. they produce spores
c. they have chlorophyll
what is the difference between a virus and a viroid? a. viroids have a higher molecular weight and no protein sheath b. viroids have a lower molecular weight and a sturdy protein sheath c. viroids have a lower molecular weight and no protein sheath d. viroids have the same molecular weight and a sturdy protein sheath
c. viroids have a lower molecular weight and no protein sheath
what is an example of a double strand DNA virus?
cauliflower mosaic virus
what is Peronospora tabacina?
causes blue mold of tobacco - almost destroyed entire tobacco industry in Cuba (1979)
what is Plasmopara viticola?
causes downy mildew of grapes - less severe on American grape species but led to the discovery of the first fungicide (Bordeaux mixture)
what is Peronospora sparasa?
causes downy mildew of roses - recent losses to Texas nurseries
what is Peronosclerospora sorghi?
causes downy mildew of sorghum - frequent outbreaks in Texas
what are symptoms of corn smut?
causes galls on host plant, hyperplasia and hypertrophy.
what is a primary inoculum?
causes original infection at the beginning of the growth season, produces primary infections
what is cedar apple rust?
causes rust symptoms on apple fruit but also infects eastern red cedar with galls
what are cytokinins?
cell division and differentiation, especially in roots
what are gibberellens?
cell elongation, named for Gibberella fujikuroi, foolish seedling disease of rice that causes excessive elongation of young plants
how do virulence factors relate to the destruction of structural integrity of plant cells?
cell-wall degrading enzymes
what is the mechanism of gall formation?
cells enlarge due to high levels of auxin production
what is a sign of sclerotinia disease? a. fruit decay b. cottony white mass of mycelium on infected tissue c. spotting and yellowing of leaves d. a & b
d. a & b
satellite viruses: a. encode their own coat protein b. need a helper virus for replication c. affect the disease symptoms of the helper virus d. all of the above
d. all of the above
what groups of pathogens can NOT be tested with Koch's postulates? a. viruses b. mildews c. rusts d. all of the above
d. all of the above
which of the following are examples of viroids? a. potato spindle tuber b. chrysanthemum stunt c. coconut cadang-cadang d. all of the above
d. all of the above
which of the following are natural openings of plants? a. stomata b. lenticels c. nectaries d. all of the above
d. all of the above
which of the following are pathogen lifestyles? a. biotroph b. necrotroph c. hemibiotroph d. all of the above
d. all of the above
which of the following is an important role of fungi? a. cycle nutrients through ecosystems by breaking down dead organic material b. supply essential nutrients to plants through mycorrhizae c. provide numerous drugs, food, and other products d. all of the above
d. all of the above
which of the following are NOT included in the disease cycle? a. penetration b. dissemination c. overwintering/oversummering d. germination e. infection
d. germination
the most common and economically most important means of transmission of most viruses in the field is by: a. pollen b. mechanical transmission c. dodder d. insect vectors
d. insect vectors
what are the two races of fungus that cause southern corn leaf blight? a. race p and q b. race s and t c. race o and m d. race o and t
d. race o and t
which of the following are NOT ways that a pathogen can infect a plant? a. wound openings b. physical force c. natural openings d. through water
d. through water
what is R gene resistance?
most common kind of resistance that operates against all types of pathogens and insects
what is the host of downy mildews?
most cultivated grains and vegetables, ornamentals, and many field crops
what makes a vulnerable host?
poor health - wounded or weakened plants can be more vulnerable, and a lack of resistance genes
what is the most effective strategy for controlling fire blight of pear?
pruning limits the presence of primary inoculum but it can be difficult
what does a plant with phosphorus deficiency look like?
purple leaves!
what is Puccinia graminis f.sp. tritici?
race of rust specific to wheat
what is Puccinia graminis f.sp. hordei?
race of rust that infects barley
what is vertical host resistance?
race specific, generally one or a few resistance genes, generally easier for a pathogen to defeat, and stable to environmental influence **all or nothing!
what are some symptoms of BYDV on wheat?
red/yellow leaf tips, stunting, reduced yield
why is it sometimes difficult to diagnose nematodes?
symptoms are not always obvious and are frequently confused with other causes
what is the fast phase of the secondary cycle?
systemic movement is known to occur in the phloem for several viruses
what is the relationship between organism complexity and treatment?
the more complex an organism, the more targets it has to kill because each organelle has a specific weakness. viruses are so simple that we cannot design something to kill them without also harming the host.
what is Dutch Elm Disease?
the most destructive shade tree disease in the US because it can kill an elm in 3 weeks by clogging water-conducting vessels - it attacks all American and European elms and once infected the tree must be removed and burned.
how does P. infestans operate as a hemibiotroph?
the pathogen initially produces effectors that suppress plant defense responses, but later it produces necrosis-inducing effectors
when was citrus canker introduced in U.S.?
the pathogen is endemic to Japan, Asia, Africa, and South America, but was first introduced in Texas in 1910 and later found in Florida in 1912-1913.
How is Oak wilt spread?
the pathogen moves through root grafts, trees within 50 feet often have a common root system so when one tree becomes infected it's easy for the pathogen to spread.
what is Physoderma?
the pathogen that causes black wart of potato, a serious potato disease. the spores released by tumors can live for up to 30 years in the soil. amplified in cold, damp climates.
what is transcription?
the process of making RNA from DNA
what is budding?
the production of a small outgrowth from the parental cell. the nucleus of the parental cell divides and one daughter nucleus migrates to the bud
how does milk control TMV?
the proteins in milk inhibits the virus and can be used as a dip during transplanting
what is phylum Ascomycota?
"ascomycetes" or sac fungi. have a sexual stage and an asexual stage.
what is phylum oomycota?
"oomycetes" examples are Pythium spp., Phytopthora infestans, and downy mildews
what is phylum plasmodiophoromycota?
"plasmodiophoromycetes", example Plasmodiophora brassicae
what is a nectotroph?
"smash and grab" pathogens that kill cells and consume the contents
what is the difference between (+) and (-) single strand RNA?
(+) RNA are faster to replicate in cell because RNA sequence is directly translated into proteins (no transcription required). (-) RNA must be transcribed before it can be translated into proteins.
what is the difference between +RNA and -RNA?
+RNA are faster to replicate within the cell because RNA sequence is directly translated into proteins, -RNA takes longer because it must be transcribed before it can be translated into proteins.
what are some characteristics of BYDV?
1. +ssRNA virus 2. phloem limited 3. aphid vectored
what are the major characteristics of TMV?
1. +ssRNA virus 2. encodes 4 proteins (2 for replication, one for movement, and one coat protein) 3. helical virion structure - rigid rod with hollow core
survival of TMV occurs in many conditions, what are they?
1. 200 F in sap, 250 F in dried leaves 2. dried leaves >50years 3. infected sap 4-6 weeks
ways to control southern corn leaf blight:
1. resistant hybrids 2. residue management - crop rotation to a non-host crop 3. fungicide application
name at least 5 of the 8 the structural elements of bacteria:
1. DNA has 1-3 chromosomes 2. plasmids 3. ribosomes 4. capsule and extracellular polysaccharide 5. cytoplasmic membrane (inner membrane - lipid bilayer) 6. peptidoglycan in cell walls 7. lipopolysaccharide (LPS) outer membrane 8. flagella common
describe the genera Agrobacterium:
1. rhizosphere and soil inhabitants 2. mostly cause galls and deformations on roots or stems 3. short, motile rods
what are the three specializations of Fusarium oxysporum and what do they attack?
1. F. oxysporum f.sp. conglutinans (cabbage) 2. F. oxysporum f.sp. pisi (peas) 3. F. oxysporum f.sp. lycopersici (tomato)
uses of LSD:
1. It was first derived from ergot mass and used as a treatment for psychiatric disorders, but medicinal use became illegal in 1968. 2. Tested by the CIA as a mind control drug that allowed people to recall memories.
name 3 important pathovars of P. syringae:
1. P. syringae pv. syringae 2. P. syringae pv. phaseolicola 3. P. syringae pv. tomato
what are the human symptoms when diseased grain (ergot of wheat and rye) is ingested?
1. mental aberrations 2. hallucinations of burning skin 3. spontaneous abortions 4. gangrene infections
how do Fusarium and Verticillum differ?
1. Verticillium are prominent in cool climates, Fusarium thrive in warmth 2. Verticillium are not host specific, Fusarium are very host specific
what are the four methods of fungal growth?
1. apical elongation 2. tropisms 3. branched hyphae 4. budding
what are the 4 types of sexual spores (meiospores)?
1. ascospores 2. oospores 3. zygospores 4. basidiospores
how do we control southern bacterial wilt?
1. avoidance - plant in cool climates 2. eradication - crop rotation 3. exclusion - disease free "seed" 4. resistant varieties 5. biological control - avirulent strain of Ralstonia solanacearum
what are the problems with control methods of fire blight of pear?
1. bacteria develop antibiotic resistance rapidly 2. other human pathogens exposed to the strain might become resistant 3. bacteria develop resistance to copper-based sprays in Bordeaux Mixture and copper can damage fruit
what do Fusarium and Verticillum have in common?
1. both are soil inhabitants and infect through roots 2. both are effective saprophytes that become permanent inhabitants in the soil once established
what 4 things do you need to know about a pathogen that has newly arrived?
1. can they survive on other plants? 2. are they biotrophic? 3. do they have major resistance genes? 4. what are their mechanisms for resistance?
how are losses accumulated through bacterial canker of stone fruits?
1. cause cankers on branches and in main trunks 2. mortality of 10-75% 3. buds and flowers are killed, reducing yield by 10-20%, sometimes up to 80%
how do viruses move?
1. cell to cell through plasmodesmata 2. long distance (systemic) through vascular system 3. plant to plant by vectors
what agricultural practices are conductive to plant disease?
1. cheap 2. abundant 3. high quality
which phylum are in kingdom fungi?
1. chytridiomycota 2. zygomycota 3. ascomycota 4. basidiomycota
what are the 7 key characteristics of viriods?
1. circular stranded (ss)RRNAs 2. smallest known pathogens 3. depend on host enzymes for replication 4. no evidence they encode proteins 5. similar symptoms to virus 6. transmitted by mechanical means 7. overwinter in perennial hosts
what are two diseases caused by Xanthomonas?
1. citrus canker 2. rice bacterial blight
how do we control bacterial speck of tomato?
1. clean seed 2. sanitation 3. copper based sprays
how do we control bacterial spot of tomato and pepper?
1. clean seed 2. copper based sprays
how is ergot controlled?
1. clean seed 2. crop rotation 3. deep tillage - sclerotia do not survive more than 1 year and do not produce spores if more than 4 inches deep
how do we control black rot of crucifers?
1. clean seed 2. sanitation 3. copper sprays
what agricultural practices caused coffee rust to occur?
1. coffee was grown over 400,000 acres in Sri Lanka 2. both pathogen and host were introduced to a new location with no effective control for the pathogen
ergot of wheat and rye effects on humans:
1. consuming infected grain resulted in "Holy Fire" or "St. Anthony's Fire" because of the burning sensation in the skin and the number of people hospitalized for it 2. most common among rural poor who used rye for bread 3. not contagious 4. young people were the most susceptible
what are the 5 ways that pathogens attack plants?
1. contact or attraction 2. adherence 3. recognition between pathogen and host 4. differentiation of infection structures 5. attack mechanisms
how did the environmental conditions in Ireland contribute to late potato blight?
1. cool, moist conditions accelerate the rate of disease 2. summer of 1845 started hot and dry 3. weather changed 1.5 to 7 degrees C below normal 4. continuous overcast and rain for 6 weeks accelerated pathogen lifecycle by 10x 5. within weeks the potato crop was destroyed
how is sclerotinia controlled?
1. crop rotation 2. deep plowing 3. fumigation 4. biocontrol
how do pH extremes affect growth?
1. denature enzymes 2. affect protein structure and activity 3. hydrolyze proteins
what do modern agricultural practices demand?
1. dense cropping system 2. over large areas - "economy of scale" 3. genetic uniformity - monoculture
what are Koch's postulates?
1. describe the symptoms in detail 2. isolate and purify the pathogen and describe it 3. inoculate healthy plants with the purified pathogen to produce the same symptoms in #1 4. reisolate the pathogen to produce the same description as #2
what are the four main types of impairment of the host caused by pathogens?
1. destruction of structural integrity 2. altered host metabolism 3. altered genetic controls 4. interference with transport (translocation and transpiration)
what are the effects of nematodes on plants?
1. reduced yields 2. increased susceptibility to environmental stress 3. predispose plants to other pathogens
name 4 important things about Basidiomycetes:
1. dikaryotic vegetative hyphae 2. septate hyphae 3. chitin in cell walls 4. sexual cycle
what are characteristics of Basidiomycetes?
1. dikaryotic vegetative hyphae 2. septate hyphae 3. chitin in cell wall 4. sexual cycle
name 4 important things about Oomycetes:
1. diploid vegetative hyphae 2. multinucleate coenocytic hyphae 3. glucans in cell walls 4. sexual cycle
what are the three methods of penetration?
1. direct penetration 2. natural openings 3. through wounds
how is Septoria spp. controlled?
1. disease free seed 2. deep plowing of plant material 3. resistant varieties 4. fungicides
how are abiotic diseases controlled?
1. do not expose to extreme environments 2. do not expose to pollution or other chemicals
how is brown patch controlled?
1. do not over fertilize in autumn 2. good surface drainage - do not water at night 3. keep less than 2cm thick 4. apply fungicides in Sept and Oct
name some important features of a eukaryotic plant cell:
1. endoplasmic reticulum 2. mitochondria 3. ribosomes 4. golgi bodies 5. vacuoles 6. perioxisome
name 4 important pectinases:
1. endopolygalacturonase 2. exopolygalacturonase 3. pectin methylesterase 4. pectin lyase
what is the general life cycle of a virus?
1. entry into host cell 2. uncoating 3. gene expression 4. replication 5. assembly 6. movement 7. moves to healthy host cell
what are virulence/pathogenicity factors of pathogens?
1. enzymes 2. toxins 3. growth regulators 4. plugging substances (polysaccharides in wilt causing pathogens)
what are the factors of pathogenicity?
1. enzymes 2. toxins 3. growth regulators 4. polysaccharides
how is DED controlled?
1. eradication - sanitation, removing breeding sites for insects (dead logs, infected trees) 2. protection - control of beetle vector via insecicides 3. host resistance 4. therapy - with fungicides like Benomyl injected into the tree or sprayed on leaves
how is stem wheat of rust controlled?
1. eradication of barberry 2. fungicide application 3. host resistant wheat 4. horizontal resistance 5. plant multiline wheat cultivars
what is the problem with using chemical control on nematodes?
1. expensive 2. difficult to apply 3. toxic to animals and humans
what are the mechanisms of virulence for southern bacterial wilt?
1. extracellular polysaccharides 2. plant hormones (auxin, cytokinin, ethylene) 3. enzymes (cellulase, pectinase, protease)
types of crops affected by disease:
1. field crop 2. vegetable 3. fruit tree 4. forest 5. turf 6. diseases of ornamentals
what are the four causal agents of fungal vascular wilts in Ascomycetes?
1. fusarium 2. verticillium 3. septoria 4. colletotrichum
name two examples of how nematode infection predisposes plants to infection with other pathogens
1. fusarium can invade nematode damaged tissues more easily 2. Ralstonia solanacearum enters through mechanically damaged roots caused by nematodes
what are some characteristics of Ascomycetes?
1. haploid vegetative hyphae 2. septate hyphae 3. chitin in cell wall 4. sexual stage - produce ascospores
name 4 important things about Ascomycetes:
1. haploid vegetative hyphae 2. septate hyphae 3. chitin and glucan in cell walls 4. undergo sexual cycle
what were the two major contributions of H. Marshall Ward?
1. he discovered that applying fungicide before the fungus arrives prevents infection (disease forecasting) 2. monoculture created the perfect situation for an epidemic
how do we control rice blight?
1. resistant cultivars 2. clean seed
what are some environmental effects on Pythium?
1. high temperatures give direct oospore or sporangia germination, low temps give indirect germination via zoospores 2. moisture is required for zoospores to infect the host 3. excess nitrogen in soil favors disease
what are the four methods used for identifying plant viruses?
1. host indexing 2. electron microscopy 3. immunoassays 4. PCR amplification
why are nematodes generally overlooked as agents of disease in plants?
1. host plants are rarely killed 2. most nematodes are root pathogens - damage is below ground 3. symptoms are often similar to those of nutrient deficiencies
7 ways to control plant pathogenic bacteria:
1. host resistance 2. sanitation 3. crop rotation 4. vector control 5. seed sterilization 6. chemical control 7. biological control
what are the two reasons for tissue growth in galls?
1. increased cell division or hyperplasia 2. increased cell size or hypertrophy
what is the source of inoculum of rice blight?
1. infected seed 2. inoculum survives on rice stubble 3. survives on alternative host 4. irrigation water
what is the life cycle of a root-knot nematode?
1. infection (2nd stage larvae) 2. penetration (behind root tip) 3. establishment of feeding site via giant cells 4. males leave root, females remain attached 5. eggs can overwinter or hatch J2 larvae
describe the infection cycle
1. inoculation 2. infection [3. attachment 4. penetration 5. host recognition 6. invasion 7. colonization 8. growth/reproduction] 9. symptom development 1/2. dissemination of pathogen (secondary inoculum) OR 10. production of overseasoning stage 11. dormant period 12. primary inoculum repeat
there are 8 methods of dissemination of plant viruses, what are they?
1. insects 2. nematodes 3. fungi 4. parasitic plants 5. humans 6. seed transmission 7. grafting 8. vegetative propagation
describe the genera Xanthomonas:
1. leaf spots and blights 2. small, motile rods
what are some typical symptoms of a virus?
1. local lesion 2. chlorosis 3. mosaic 4. ring spot 5. systemic symptoms
describe the genera Pseudomonas:
1. localized rots, leaf spots and blights 2. greenish, water soluble pigment in culture 3. motile rods
for a pathogen to infect a plant it must be able to:
1. make its way into and through the plant tissues 2. obtain nutrients from the plant 3. neutralize or disarm the defense reactions of the plant
how is TMV transmitted?
1. mechanically by man, NOT BY INSECTS 2. grafting 3. dodder 4. seed-transmitted 5. not by pollen
what are the different classifications of systemic symptoms?
1. mosaic patterns 2. yellowing 3. dwarfing 4. necrosis 5. malformation
describe the genera Clavibacter:
1. most common gram (+) genus 2. cause systemic infections producing galls and wilts 3. slender, non-motile rods
which phylum are in kingdom protozoa?
1. myxomycota 2. plasmodiophoromycota
what are the four types of Ascocarps in Ascomycetes?
1. naked asci 2. cleistothecium 3. perithecium 4. apothecium
history of potatoes:
1. native to Andean highlands in Peru and Bolivia and a staple food since 400 BC 2. imported to Europe by Spanish conquistadors in 1750 3. widely accepted in Europe by 1800's due to nutrition, yield, and ease of growth
characteristics of prokaryotes
1. no membrane bound nucleus 2. no mitochondrial DNA 3. no visible endoplasmic reticulum 4. some are limited to growing in the vascular tissues of plants
what are some characteristics of non-infectious disease?
1. no pathogen involved 2. usually caused by lack of or excess of something that supports life 3. usually differ in symptoms from biotic agents and cause more random patterns
what are the types of viral-insect relationships?
1. non-propagative - virus does not replicate in vector 2. propagative - virus replicates in vector and is persistent
what are 7 characteristics of a virus?
1. nucleic acid contained within protein particle/capsid 2. lack ribosomes 3. no metabolism 4. no cell 5. no division 6. reproduction by replication 7. not sensitive to antibiotics
what were the steps for the citrus canker eradication campaign?
1. nursery and grove inspections 2. on site destruction of canker infested trees and entire canker infected nursery 3. sanitation procedures 4. strict quarantine enforcement
what are the characteristics of Puccinia graminis that causes stem rust of wheat?
1. obligate parasite 2. very host specific 3. heteroecious, macrocyclic rust 4. worldwide distribution
what are 7 characteristics of plant parasitic nematodes?
1. obligate parasites 2. small size 3. feed by stylet 4. remain outside of the host cell 5. movement requires moisture 6. females are dominant form 7. well developed chemosensory system
what are the 4 characteristics of a desirable biological control agent?
1. occupies the same ecological niche 2. can outcompete or antagonize the pathogen 3. can be applied prior to the arrival of the pathogen inoculum 4. has resistance to antibiotics used to control pathogen
what are the three main groups of plant pathogenic fungi?
1. oomycetes 2. ascomycetes 3. basidiomycetes
which phylum are in kingdom chromista?
1. oomycota
what are the three lifestyles of fungi?
1. parasitism (cause disease) 2. saprophytism (growing on dead matter) 3. symbiosis (grow together with organisms)
what are the two types of genes for pathogen infection?
1. pathogenicity genes 2. avirulence genes
reasons for Ireland's dependence on potatoes:
1. peasants consumed 8-14 pounds a day 2. potatoes grew well in moist climate 3. similar nutrition as grain crops but only used half the land 4. peasants paid rent with grain crops and ate the potatoes 5. by 1845 there was no significant food alternative
mechanisms for plant resistance:
1. pre-formed barriers (bark, cell wall, biochemical barriers) 2. active responses initiated by the host after challenge 3. combinations of both
what are the phases of penetration?
1. pre-penetration 2. penetration
what are the three kingdoms of fungi?
1. protozoa 2. chromista 3. fungi
challenges of plant pathologists:
1. reduce food losses 2. improve yield and food quality
pathogens accomplish infection through:
1. secretions of chemical substances to destroy plant tissue structures or to affect metabolic mechanisms of the host 2. mechanical force to penetrate and invade plant tissues
what is the source of inoculum for black rot of crucifers?
1. seed 2. transplant from contaminated seed 3. plant debris
what is the source of inoculum for bacterial speck of tomato?
1. seed 2. transplants from contaminated seed 3. plant debris
what is the source of inoculum for bacterial spot of tomato and pepper?
1. seed 2. transplants from contaminated seed 3. plant debris
describe the genera Erwina and Pectobacterium:
1. some cause necrotic or wilt diseases 2. others cause soft rots 3. motile rods
what are the two disease theories?
1. spontaneous generation 2. germ theory
what are some environmental determinant that affect the growth of plants?
1. temperature 2. moisture 3. oxygen 4. light 5. pH 6. nutrient deficiencies 7. pollution 8. toxic minerals 9. herbicides
name the 6 environmental variables that must be taken into account for disease development:
1. temperature 2. moisture 3. wind 4. light 5. soil pH 6. host plant nutrition
describe the genera Streptomyces:
1. the only one that produces hyphae, no crosswalls, and gram (+) 2. all soil inhabitants 3. many produce antibiotics
what methods do cereal rusts use to penetrate hosts?
1. thigmotropic - locate stomate opening on physical leaf surface 2. chemotropic - structures can be induced by volatile compounds from the host
name 2 examples of specific viral diseases?
1. tobacco mosaic virus (TMV) 2. barely yellow dwarf virus (BYDV)
what is the evidence for the role of victorin in disease development of victoria blight of oats?
1. toxin action and oat susceptibility are correlated. 2. application of toxin itself produces all external symptoms, histochemical and biochemical changes in host cell. 3. degree of toxin production and virulence of pathogen are correlated 4. tox-negative mutants do not produce disease
what are the components of the disease triangle?
1. virulent pathogen 2. susceptible host 3. conducive environment
what are the symptoms of southern bacterial wilt?
1. wilting 2. stunting/distortion of plants 3. discolored vascular tissue 4. bacterial ooze from cut stems
describe the genera Xyllela:
1. xylem inhabiting 2. fastidious bacteria
what are the 5 types of asexual spores?
1. zoospores 2. conidia (singular: conidium) 3. sporangiospores 4. arthrospores 5. chlamydospores
what was the difference in losses due to southern corn leaf blight in 1969 vs. 1970?
1969 was mild with <2% of losses and by 1970 $1 billion worth of losses in the United States.
why is plant pathology important?
36.5% of crops are lost annually ($550 billion), 14.1% due to diseases
what effects Phytophthora germination?
50-68 F leads to indirect germination with multiple zoospores (8) per sporangia. 68-77 F leads to direct germination with a single germ tube and penetration via an appressorium.
where is the environment conducive for Ralstonia solanacearum?
>85 degrees F (tropical, subtropical, and warm temperate regions) no disease below 65 degrees F
what is the advantage of producing opines to the bacterium?
Agrobacterium strains carry genes for utilizing opines which provide the bacteria with a carbon and nitrogen source that they can use, but the plant cannot.
what is ergotamine?
Alkaloids that cause muscular contractions and spontaneous abortions. It can also prevent hemorrhaging after birth and migraine headaches.
what does Dutch Elm Disease (DED) look like?
As early as June, the leaves on a DED-infected elm will wilt, turn yellow, then curl and turn brown. Initial symptoms include wilting and chlorosis of affected branches above the point of infection (so-called "flagging").
what is an example of wood rotting fungi?
Bracket or shelf fungus on tree that forms a conk
what pathogen causes Oak Wilt?
Ceratocystis fagacearum
what pathogen causes DED?
Ceratocystis ulmi
what pathogen causes chestnut blight?
Cryphonectria parasitica
what is the central dogma of biology?
DNA or RNA is transcribed into RNA which is then translated into proteins that complete biological and biochemical functions
who discovered Lysergic Acid Diethylamide (LSD)?
Discovered by Dr. Albert Hoffman when he was looking for circulatory stimulants in extracts from ergot
why is fire blight of pear a new encounter disease?
Erwinia amylovora is native to North America and has since spread to New Zealand, England, and elsewhere in Europe - the infection is not severe on native hosts like hawthorn and mountain ash, but is a serious problem for introduced hosts
what is the ecological niche of the fire blight pathogen?
Erwinia amylovora lives as an epiphyte on pear blossoms and in cankers awaiting conducive conditions
what insects are vectors for DED?
European Bark Beetle and Native Elm Bark Beetle because females make their egg chambers in the wood of dead/dying trees and feed on young tissue - the Native Elm Bark Beetle can fly up to 2km to search for healthy elms to feed on
F/F: cyst nematode forms a feeding site called a giant cell
FALSE
T/F: for transmission, tobacco mosaic requires nonlethal mechanical wounding of plant cell
FALSE
T/F: symptoms alone are usually sufficient to identify specific viral diseases and the viruses that cause them
FALSE
T/F: viruses contain both DNA and RNA
FALSE
T/F: tobacco mosaic virus only infects tobacco plants
FALSE - TMV infects >150 genera of hosts including tomato, apple, grape, and others
T/F: symptoms alone are enough to diagnose a viral disease
FALSE - names are derived from the symptoms they cause and the host they affect but symptoms alone do not account for all considerations.
T/F: rusts are facultative parasites
FALSE - they are OBLIGATE parasites
T/F: nematodes are structurally complex organisms
FALSE - they are simple with digestive, nervous, excretory, and reproductive systems
T/F: rusts are non-host specific
FALSE - they are very host specific
T/F: cell to cell movement of viruses is accomplished via endoplasmic reticula
False
T/F: citrus canker occurs in Texas since the 1980s
False
T/F: growth and reproduction do not occur concurrently with infection
False
T/F: there is only one kind of inoculum
False
T/F: thigmotropism does not play a major role in the location of infectable sites on plants by fungi
False
T/F: sexual reproduction of fungi is the most harmful to plants
False - asexual reproduction is the most harmful
T/F: root-knot nematodes penetrate roots and move to vascular tissue and use syncitial feeding structure
False - cyst nematodes do this
T/F: germination is through stomates and penetration requires free water
False - germination requires free water and penetration is through stomates
T/F: gram (-) bacteria stain, gram (+) bacteria do not stain
False - gram (-) bacteria do not stain, gram (+) bacteria stain
T/F: Prevost's theory was widely accepted by the scientific community
False. Germ theory was rejected and people continued to believe that mildews, rusts, rots, and microorganisms were products of disease rather than the cause.
T/F: monoculture is a sustainable way to grow crops
False. Monoculture's result in famine.
T/F: fungus are grouped in a simple classification system
False. Their numbers are huge and their classification is complex.
what is ergot?
French for "spur." Occurs when the size of the sclerotium (fungus fruiting body) is host plant dependent and reduces yield because seeds are replaced by sclerotia or ergot.
who is Robert Koch?
German microbiologist who developed a scientific method for understanding the roles of specific microorganisms as causal agents for disease through his anthrax-sheep study
when was the last recorded epidemic of late blight?
Germany in 1916. Copper fungicides had been discovered and were used to control the disease, but the German army used the copper for bullets instead. 700,000 people died.
what is a hypersensitive response?
HR is programmed cell death process triggered in response to incompatible pathogens that leads to cell and tissue death in 24 hours after infection
what is the host and pathogen of chestnut blight?
Host: American chestnut (Castanea dentata) Pathogen: Cryphonectria parasitica (Endothia parasitica)
what is the host and pathogen of coffee rust?
Host: coffee (Coffea arabica) Pathogen: obligate fungus (Hemileia vastatrix)
what is the host and pathogen of southern corn leaf blight?
Host: corn (Zea mays) Pathogen: Cochliobolus heterostrophus (Bipolaris maydis)
what were the host the and pathogen in the Irish potato famine?
Host: potato (Solanum tuberosum) Pathogen: oomycete (Phytopthora infestans)
what is the host and pathogen of ergot of wheat and rye?
Host: wheat, rye, oats Pathogen: Claviceps purpurea
what pathogen causes brown rot of stone fruits?
Monilinia fructicola
is late potato blight a case of "New Encounter" disease?
No. Potatoes and Phytopthora infestans were both imported from South America, but in S.A. the genetic base of the host provides natural resistance.
what pathogen causes bacterial soft rots of vegetables?
Pectobacterium carotovorum causes rotting of potato tubers in the field and in storage
what does Phytophthora infestans translate to?
Phyto = plant, phthora = killer, infestans = infectious
what causes sudden oak death?
Phytophthora ramorum
what is the biological control agent for Erwinia amylovora?
Pseudomonas fluorescens because it competes for resources on the leaf surface and is resistant to antibiotics used to treat fire blight, and is not pathogenic.
what is an example of a pathovar?
Puccinia graminis pv. tritici infects wheat
what diseases are caused by phylum Oomycota?
Pythium spp., Phytopthora infestans, and downy mildews
what is the difference between race O and race T?
Race O is the old race and is not virulent and Race T is virulent on corn containing TMS, but both produce phytotoxins
what pathogens are in Phylum Zygomycota?
Rhizopus and Mucor - soft rot of fruits and vegetables
what is an example of a satellite virus?
Satellite panicum mosaic virus (SPMV) with the helper Panicum mosaic virus
what is the disease cycle of Septoria spp.?
Septoria overwinters as mycelium and as conidia within pycnidia on and in infected seeds
coffee is now grown in _______________, where the pathogen that causes coffee rust has been excluded by quarantines for over 100 years until ______.
South America; 1970
what pathogen causes powdery mildew of rose?
Sphaerotheca pannosa
what is witchweed?
Striga species that causes major losses of cereal production in sub-saharan Africa - the greatest food production obstacle in Africa that affects maize, sugarcane, and rice.
T/F: Fusarium oxysporum and all it's forma speciale are monocyclic
TRUE
T/F: Rhizoctonia solani does not produce any asexual spores and only occasionally produces sexual spores
TRUE
T/F: cereal rusts penetrate hosts through stomates
TRUE
T/F: cool and moist spring time conditions favor development of BYDV
TRUE
T/F: in stem rust of wheat symptoms are produced on almost all aerial parts of the wheat plant but are most common on stem and leaf
TRUE
T/F: most smut fungi only produce teliospores and basidiospores
TRUE
T/F: nematodes are the most numerous animals on Earth
TRUE
T/F: satellite viruses differ from satellite RNA in that satellite viruses encode their own coat protein
TRUE
T/F: seed borne septoria causes damping-off disease
TRUE
T/F: viruses are obligate parasites
TRUE
T/F: viruses enter hosts by mechanical wounding provided by vectors
TRUE
T/F: the most damaging nematodes are endoparasitic species
TRUE - cyst and root-knot nematodes are the most damaging
T/F: rusts are in order Uredinales
TRUE - there are about 5,000 species!
T/F: sedentary endoparasites select one feeding site for life and cause damage like cysts and root-knots while migratory endoparsites move throughout the root system and cause lesions
TRUE!
T/F: Chytridiomycetes are water and soil-inhibiting fungi, obligate parasites, and biotrophic
True
T/F: DNA can be obtained from nucleus, chloroplasts, and mitochondria in plant cells
True
T/F: Dutch elm disease has spread throughout North America and destroyed over half the elm trees in the north US
True
T/F: Dutch elm disease was first described in the Netherlands in 1921 and found in US in 1930
True
T/F: Florida was declared canker free in 1927 and U.S. in 1947
True
T/F: Pseudomonas and Xanthomonas make up almost all bacterial spots, blights of leaves, stems, or fruits
True
T/F: Septoria spp. has conidia borne in pycnidia or a flask shaped structure
True
T/F: a spore-producing body is called a fruiting body or a sporocarp
True
T/F: all bacteria are prokaryotes
True
T/F: bacteria have plasmids, small circular chromosomes
True
T/F: bacteria infect plants between their cells
True
T/F: basidiospores are produced on the outside of the basidium that is derived from a teliospore
True
T/F: certain fungi align themselves on plant surfaces according to touch and grow along grooves or through natural openings
True
T/F: chestnut blight is caused by Ascomycetes
True
T/F: colonists brought pears and apples that did not coevolve with Erwinia amylovora and are very susceptible to the pathogen
True
T/F: components of the disease triangle can vary, affecting the severity of the disease
True
T/F: downy mildews are diploid in their vegetative state
True
T/F: estimates put worldwide economic damage due to plant viruses as high as $60 billion/year
True
T/F: every plant species can be effected by pathogens
True
T/F: fungal vascular wilts are one of the most important types of plant diseases
True
T/F: fusarium and verticillium were considered deuteromycetes, but they undergo parasexual cycles
True
T/F: germ tubes of a certain rust fungi grow perpendicular to rows of stomates to increase likelihood of encountering a stomate for entrance into the leaf
True
T/F: gram (+) bacteria is more sensitive to antibiotics, while gram (-) bacteria can be difficult to control
True
T/F: local lesions usually develop near the site of entry on the leaves or fruit
True
T/F: members of kingdom fungi have mycelium and their cell walls contain glucans and chitins but lack chloroplasts
True
T/F: names of sexual spores are based on the phyla they come from
True
T/F: necrotrophs are NOT controlled by major resistance genes
True
T/F: on a culture slide Pseudomonas is green while Xanthomonas is yellow
True
T/F: one of the most important diseases of stone fruit is bacterial canker of stone
True
T/F: pathogen resistance and host susceptibility are genetically determined
True
T/F: pectinase is the most important enzyme in disease development
True
T/F: phytoplasmas are vectored by leaf hoppers
True
what order are smuts a part of?
Ustilaginales - 1200 species of smut fungi
what pathogen causes corn smut?
Ustilago maydis
what is Pseudomonas syringae pv. syringae?
a bacterial pathogen to many plant hosts that produces a water soluble pigment called pyoverdin that fluoresces in iron limited medium.
what is Pseudomonas syringae pv. phaseolicola?
a bacterial pathogen to only bean plants
what is Pseudomonas syringae pv. tomato?
a bacterial pathogen to only tomato
what is fire blight of pear?
a disease caused by Erwinia amylovora that affects over 130 plant species in the rose family (apple, crabapple, pear, mountain ash)
what is bacterial canker of stone?
a disease caused by Pseudomonas syringae pv. syringae that infects cherries and other stone fruits. "gum" is bacterial ooze that tastes sweet because of polysaccharides.
what is citrus bacterial blast?
a disease caused by Pseudomonas syringae pv. syringae; bacteria infects small injuries on leaves/twigs of citrus plant and results in black spots on fruit and leaves.
what is bacterial speck of tomato?
a disease caused by Pseudomonas syringae pv. tomato that produces coronatine (chlorosis inducing toxin)
what is black rot of crucifers?
a disease caused by Xanthomonas campestris pv. campestris that results in V-shaped black rot lesions on cabbage
what is bacterial spot of tomato and pepper?
a disease caused by Xanthomonas campestris pv. vesicatoria that damages the leaves, stems and fruit
what is the Robigalia?
a festival in ancient Roman culture that included a dog sacrifice to the rust god, Robigus, to prevent rust diseases of grain crops and wheat
what are leaf blights, blasts, and spots?
a foliage disease (organs affected)
what is chlorosis?
a foliage disease (organs affected) that leads to vein clearing and/or mottling
what is haustoria?
a form of fungal/oomycete biotroph that remains outside of the plant plasma membrane and is specialized for nutrient and signal exchange
what are spots, scurf, and sunscaled?
a fruit disease (organs affected)
what is fruit rot?
a fruit disease (organs affected)
who is Theophrastus?
a greek philosopher who wrote a book about diseases of trees, cereals, and legumes in 300 B.C.
what are phytoplasmas?
a group of plant pathogenic bacteria with no cell wall - restricted to phloem vascular tissue
what is a monoclonal antibody?
a highly specific antibody that is produced to fight a particular viral protein rather than the entire particle
what is AAL-toxin?
a host specific toxin produced by Alternaria alternata that is a potent natural herbicide for tomatoes.
what is T-toxin?
a host specific toxin produced by race T of Cochliobolus heterostrophus that caused the southern corn leaf blight of 1970.
what is Texas male-sterile cytoplasm (TMS)?
a mutated gene in the mitochondria that is transmitted through the female germ line. TMS corn eliminated the need for detasseling by hand.
what is phaseolotoxin?
a non-host specific toxin that causes halo blight of bean
what is a polyclonal antibody?
a non-specific antibody that is produced by infecting an entire particle of a virus
what is the difference between a parasite and a pathogen?
a parasite is dependent on a host for its life functions and a pathogen is any organism capable of producing disease even if the symptoms are not felt
define obligate parasite
a parasite that can grow ONLY in association with a living host
define species
a population of organisms with common morphological and physiological characteristics that allow for consistent reproductive success
what is damping-off?
a root disease (organs affected) that causes seedling death just prior to or just following emergence from the soil
root rot
a root disease (organs affected) that leads to discoloration and decay due to disintegration and decomposition of tissue
what are witch's brooms?
a stem disease (organs affected) caused by parasitic plants
what are galls?
a stem disease (organs affected) that leads to hyperplasia, or an increase in the number of cells
what are cankers?
a stem disease (organs affected) that results in localized necrotic areas associated with death of the phloem
what is Puccinia graminis?
a stem rust of cereals, but some individuals of this pathogen only attack wheat while others only barley or oats
what is a latent period?
a symptomless infection period
what is a mycotoxin?
a toxin produced by a fungus
what is wilt?
a vascular disease (organs affected) that occurs when transpiration exceeds absorption and turgor in cells is lost
what is Fusarium oxysporum?
a very host specific but common pathogen that causes wilts. disease is favored by warm conditions and attacks vegetables, flowers, and herbaceous perennial ornamentals (potato and banana especially).
what is a symptom?
a visible abnormality
which of the following is not an abiotic pathogen? a. fungal infection b. too much or too little soil moisture c. toxicity of minerals or pesticides d. air pollution e. nutrient deficiencies
a. fungal infection
which of the following is an example of a Clavibacter discussed in class? a. goss' bacterial wilt of corn b. pierce's disease of grapes c. chestnut blight d. fire blight of pear
a. goss' bacterial wilt of corn
what reproductive stage is represented by the terms perfect or teleomorph? a. sexual b. asexual c. parasexual d. mutation
a. sexual
what are the two phases of the secondary cycle? a. slow phase and fast phase b. early phase and late phase c. past phase and future phase d. old phase and new phase
a. slow phase and fast phase
how can diagnosis of abiotic disease be distinguished from biotic factors?
abiotic disease can resemble virus/root pathogen/nematode symptoms so information on growth condition is important in diagnosis
what does the aerial plant surface primarily consist of? a. cellulose b. cuticle c. cutin d. a & b e. b & c
d. a & b
effect of soil pH on disease development
affects pathogen survival, growth, and development and the nutrition status of the soil
define host specificity
aka host range or the ability to cause disease on only a limited number of plant hosts - can be very specific in crop species
define pathogenicity
aka pathogenesis or the ability of the parasite to interfere with one or more of the essential functions of the plant and thereby cause disease
what is a pathovar (pv.)?
aka special forms, groups of pathogens that only attack specific varieties of plants
what is parasitic dodder?
aka strangle-weed is a filamentous plant with thread like, chlorophyll-less twining stems and short-lived root systems
define mutualism
aka symbiosis is when two organisms live in close association and both benefit from the interaction
what are the hosts of cereal rusts?
all grasses, each year about 500 billion dollars is lost to cereal rust
what is a systemic infection?
an infection throughout the host, ex. fungi and viruses
define incompatible interactions
an interaction between a resistant host and an avirulent pathogen where no disease occurs
define compatible interactions
an interaction between a susceptible host and a virulent pathogen that result in disease
define non-obligate parasite
an organism that can survive either as a parasite or a saprophyte
define facultative saprophyte
an organism that is primarily a parasite but can be a saprophyte
what is citrus greening caused by?
an unculturable, gram (-) bacterium that is phloem limited
what are bacteria names based on?
appearance of the cells: diplo (sets of 2), strepto (bacteria chains), and staphylo (grape like clusters)
what is the evidence of cutinase for pathogenicity?
anthracnose of papaya - cutinase-deficient mutants do not penetrate unless cutin is removed or wound is made. if enzyme activity is blocked there is no penetration.
what disease is caused by Colletotrichum?
anthracnoses
how is fire blight of pear controlled chemically?
antibiotic streptomycin and Bordeaux Mixture is used to control the disease
what is Apothecial or Cap fungi (Discomycetes)?
asci are contained on fruiting structures (ascocarps) shaped like cups or cushions called apothecia.
what are Pseudothecial fungi (Loculoascomycetes)?
asci in cavities within a mycelial matt ("stroma")
what are Perithecial fungi (Pyrenomycetes)?
asci in closed bodies or with an opening
what are the sexual spores of Ascomycetes called?
ascospores - generally in groups of eight within a sac
what are the symptoms of fire blight of pear?
attacks all parts of the tree and blackens the twigs, flowers, and leaves. stem and twig cankers ooze with bacteria.
what strategies do biotrophs and necrotrophs utilize to avoid detection?
bacterial pathogens grow between cells and only insert specialized feeding mechanisms!
what disease is caused by Pectobacterium?
bacterial soft rots of vegetables/potato blackleg
over how many years was the chestnut population devastated by chestnut blight? a. 20 b. 40 c. 50 d. 60
b. 40
where did the host and pathogen of coffee rust originate? a. Colombia b. Ethiopia c. Sri Lanka d. None of the above
b. Ethiopia
what is the infective stage of cyst-forming Globodera (round cyst nematode of potato)? a. J3 b. J2 c. adult female d. none of the above
b. J2
what is the infective stage of root knot Meloidogyne? a. J3 b. J2 c. adult female d. none of the above
b. J2
what pathogen causes crown wart of alfalfa? a. Olpiduim alfalfae b. Physoderma alfalfae c. Phytopthora alfalfae d. Rhizopus alfalfae
b. Physoderma alfalfae
what kind of grass does brown patch affect significantly in Texas? a. Bermudagrass b. St. Augustine grass c. Kentucky Bluegrass d. Centipedegrass
b. St. Augustine grass
what reproductive stage is represented by the terms imperfect or anamorph? a. sexual b. asexual c. parasexual d. mutation
b. asexual
what is one of the most dreaded citrus diseases known? a. citrus bacterial blast b. citrus canker c. citrus greening d. citrus black spot
b. citrus canker
what is inbreeding depression? a. continued selfing of hybrid progeny that gives increasing yield b. continued selfing of hybrid progeny that gives declining yield c. continued selfing of hybrid progeny that gives consistent yield d. continued selfing of hybrid progeny that gives no yield
b. continued selfing of hybrid progeny that gives declining yield
what is the infective stage of citrus nematode Tylenchulus? a. J3 b. female J2 c. adult female d. none of the above
b. female J2
which of the following is not a category of disease? a. organs affected and symptoms b. impact on yield c. crops affected d. pathogens
b. impact on yield
which of the following is included in the disease cycle? a. sporulation b. inoculation c. germination d. desication
b. inoculation
what is the most important mode of virus transmission? a. grafting b. insects c. fungi d. humans
b. insects - aphids, leafhoppers, white flies, and other sapsuckers
what is the term for a collection of hyphae? a. golgi apparatus b. mycelium c. septum d. hypha
b. mycelium
where does citrus bacterial blast primarily occur? a. southern california b. northern california c. southern florida d. northern florida
b. northern california
what is Xanthomonas axonopodis pv. citri?
bacteria that is rod-shaped, gram (-) and has a single polar flagellum, causes citrus canker.
what kind of pathogens are causal agents?
biotic (infectious)
what are minor elements for nutrient deficiencies?
boron, sulfer, iron, zinc, copper, manganese, and molybdenum
how does the environment affect growth and sporulation in Phytopthora infestans?
both require free moisture in the environment throughout the life cycle. if the weather becomes hot/dry, infections come to a halt.
what is Rhizopus?
bread mold
how are viruses named?
by the disease symptom they cause and the plant they affect i.e. tobacco mosaic virus
which of the following states are NOT affected by bacterial canker of stone fruits? a. Washington b. Texas c. New Mexico d. California e. Oregon
c. New Mexico
what is the infective stage of reniform Roylenchulus? a. J3 b. J2 c. adult female d. none of the above
c. adult female
where does fungal growth occur during apical elongation? a. outside of hyphae b. in the middle of hyphae c. at the tip of hyphae d. at the end of hyphae
c. at the tip of hyphae
what is a pathogen? a. only biotic factors b. only abiotic factors c. biotic and abiotic factors
c. biotic and abiotic factors
which of the following is NOT a major group of fungal pathogens? a. ascomycetes b. basidiomycetes c. chytridiomycota d. oomycetes
c. chytridiomycota
where is bacterial speck of tomato a problem? a. warm, moist temperatures b. warm, dry temeperatures c. cool, moist temperatures d. cool, dry temperatures
c. cool, moist temperatures
what is hybrid vigor? a. crossing genetically similar parents to give progeny with higher yields b. crossing genetically distinct parents to give progeny with lower yields c. crossing genetically distinct parents to give progeny with higher yields d. crossing genetically similar parents to give progeny with lower yields
c. crossing genetically distinct parents to give progeny with higher yields
root knot nematodes are: a. endoparasitic and migratory b. ectoparasitic and sedentary c. endoparasitic and sedentary d. ectoparasitic and migratory e. none of the above
c. endoparasitic and sedentary
which of the following is not a form of bacteria? a. spirilla b. bacilli c. fusilli d. cocci
c. fusilli - this is a pasta
which of the following INCORRECTLY matches the viral gene product to it's responsibility? a. movement protein; secondary spread b. RNA polymerases; replication c. helicase; packaging d. viral specific proteases; regulation
c. helicase; regulation
viruses are: a. facultative saprophytes b. facultative parasites c. obligate parasites d. strict saprophytes e. none of the above
c. obligate parasites
what is the ascocarp structure for the pathogen that causes DED? a. naked asci b. cleistothecium c. perithecium d. apothecium
c. perithecium
what is the host of Phytophthora citrophora?
citrus
what is malformation?
change in the normal shape of the plant or parts of the plant
what was a major symptom of chestnut blight?
chestnut wood is naturally rot resistant, but the pathogen causes it to rot
what are host signals during infection?
chitin, fatty acids, galacturonans, phenolics
cell walls of eukaryotic fungi are comprised of:
chitin, glucan, and cellulose
what is a symptom of iron deficiency?
chlorosis between veins!
what is phylum Chytridiomycota?
chytrids that produce zoospores with a single posterior flagellum and are haploid and coenocytic.
what is phylum Basidiomycota?
club fungi, includes rust, smut and bunt fungi
what is an envelope?
coating made of protein - not always present
what are the two types of hyphae?
coenocytic and septum (plural septae)
what is a mosaic pattern?
colors can be light green, dark green, yellow, or white. if borders between colors are sharp it is mosaic but if they are blurred it is "mottled"
what are included in Phylum Basidiomycota?
common mushroom, shelf fungi, conks, puffballs, and toadstools
what are true/leafy mistletoes?
commonly known as christmas mistletoes, these parasitic plants grow on landscape trees and are either female (produce berries) or male (produce pollen). the berries are very sticky which makes it very easily transmissible by birds.
what is microsclerotia?
compact masses of mycelial mat
what is vertical resistance?
complete resistance to certain races of a pathogen. usually single gene resistance.
what is a virion?
complete virus particle
why is the environmental component so important to the disease triangle?
conditions can change rapidly and favor either the host or the pathogen. for example, the summer of Irish potato famine had consistent cool, moist conditions which was advantageous for Phytopthora infestans
what are the asexual spores of Ascomycetes called?
conidia - form either on free hyphae or in asexual fruiting bodies
how does Verrticillium spp. infect?
conidia move through plant and germinate, microsclerotia can survive up to 15 years, fungus overwinters in soil or in host tissue.
how can citrus bacterial blast be controlled?
copper based sprays, trimming of the canker
how does Bordeaux Mixture work?
copper sulfate (CuSO4) is toxic to the fungus and plant cells, but lime reduces phytotoxicity - this is the most widely used fungicide in the world
how is eradication used to control nematodes?
crop rotation, catch crops, and physical methods like hot water and drying of roots
which of the following INCORRECTLY matches the viral gene product to it's responsibility? a. coat protein; packaging b. viral specific proteases; regulation c. helicase; unwinds DNA d. RNA polymerases; secondary spread
d. RNA polymerases; secondary spread
define virulence
degree of pathogenicity
how is self fertilization prevented in corn?
detasseling (getting rid of male flowers) and cytoplasmic male sterility
what is thigmotropism?
directional growth directed by touch in response to topographical guidance cues
what is rice bacterial blight?
disease caused by Xanthomonas oryzar that leads to severe devastation in all rice growing countries and is characterized by longitudinal lesions that develop along the leaf edge.
what is southern bacterial wilt?
disease caused by the worldwide pathogen Ralstonia solanacearum that infects banana, potato, tobacco, tomato, eggplant, and more (200+ species)
what are anthracnoses?
disease of foliage, stems, or fruits
what is the germ theory?
diseases are caused by microorganisms
what are new encounter diseases?
diseases that introduce new hosts to native pathogens or native hosts to a new pathogens
what is a common example of mutualism? a. root nodule bacteria of legume plants b. mistletoe on trees c. mycorhizal infection of roots d. b & c e. a & c
e. a & c
what factors affect nematode populations? a. susceptibility of host plant and host nutrition b. environmental factors c. biological factors d. survival in absence of host e. all of the above
e. all of the above
which of the following are examples of abiotic pathogens? a. soil pH b. lack or excess of light c. too high or too low temperatures d. improper cultural practices e. all of the above
e. all of the above
which of the following are ways that environment affects disease progress? a. dissemination b. spore development c. germination and infection d. growth and sporulation e. all of the above
e. all of the above
which of the following diseases are caused by Phylum Chytridiomycota? a. olpidium b. black wart of potato c. crown wart of alfalfa d. brown spot of corn e. all of the above
e. all of the above
which of the following were impacts of the Irish potato famine? a. 1.5 million people immigrated to the U.S. b. the U.S. was allowed to import corn to feed the Irish c. 1 million people died d. Irish-British conflict was deepened e. all of the above
e. all of the above
the greater the scale of production: a. the harder for pathogens to spread b. the easier for pathogens to spread c. the more difficult it is to apply technology d. a & c e. b & c
e. b & c
what is southern corn leaf blight?
ear infections characterized by black moldy growth on the kernels and ears of corn, inner husks that come into contact with infected kernels are also black in color.
how is avoidance used to control nematodes?
early planting in lower temperatures, avoid infested soils
what is the difference between ectoparasitic and endoparasitic nematodes?
ectoparasitic nematodes do not enter the root, they only penetrate cells from the outside. endoparasitic nematodes enter the root and leave a trail of dead cells.
describe the generalized life cycle of a nematode:
egg produced by sexual reproduction or parthenogenesis, 4 juvenile stages in most (J1 is present only in egg and J2 hatches). adult males may be absent in parthenogenetic species
what is pectinase?
enzyme that degrades pectin - kill cells and eventually burst the cell membrane due to internal pressure
what are cellulases?
enzymes that break down cellulose - produced by fungi, bacteria, and nematodes
what are proteinases?
enzymes that break down proteins
what are hemicellulases?
enzymes that degrade hemicellulose which is a complex mixture of polysaccharide polymers
what are liginases?
enzymes that degrade lignin (plant strengthening) that have an aromatic structure consisting of phenylpropane units linked together as a polymer (example: white rot fungus that affects tree trunks)
what are lipases?
enzymes that degrade lipids
what are amylases?
enzymes that degrade starches
what is a binding site of a coat protein called?
epitope or antigenic determinant
what is a fungus?
eukaryotic, heterotrophic, absorptive organisms that develop a rather diffuse, branched, tubular body and reproduce by means of spores.
effect of host plant nutrition on disease development
example: high nitrogen content in soil often promotes diseases
what is apical elongation?
extension of fungal growth from the tip of the hyphae, new material develops the "apical dome"
_____________ bacteria are limited to growing in the phloem or xylem of plants
fastidious
describe the sexual cycle of Phytophthora:
female organs (oogonia) and male organs (antheridia) form and leads to the diploid oospore (zygote)
what disease is caused by Erwinia?
fire blight of pear
what are the symptoms of ozone damage?
flecking, stippling on upper surface of leaves, necrosis
how does high soil moisture affect plants?
flooding or excessive watering results in anaerobic soils which alters metabolism of toxic compounds
what is the pre-penetration phase?
follows the "arrival" of inoculum but requires several critical events for disease to occur.
how has Japan successfully quarantined pears?
for years they had a ban on the import of plant materials of all susceptible varieties, but recently they have let small amounts in for breeding after close inspection and testing.
what is the largest category of disease causing agents in plants?
fungal diseases
effect of temperature on black root rot of tobacco
fungal pathogen (Thielaviopsis basicola) thrives at low temperatures (22-28 degrees C), during cool seasons the organism builds up in the soil and infects tobacco plants which are most susceptible in cool weather.
what are some of the methods used for controlling Pythium?
fungicides, host resistance, sterilizing soil in greenhouse, avoidance via site selection, crop rotation, shallow planting, avoid overfertilization, and biological control
what led to the dramatic change in losses of corn during the southern corn leaf blight?
genetic uniformity of crops
what is the cell wall of oomycetes composed of?
glucan and a small amount of cellulose
what are the hosts of smuts?
grains and grasses, usually considered pathogens of cereals but can affect sugarcane, onions, and some ornamentals
what is the difference between gram (-) and gram (+) bacteria?
gram (-) have thin peptidoglycan and LPS outer membrane. gram (+) have thick peptidoglycan and lack LPS outer membrane.
what Mexican delicacy is caused by the pathogen Ustilago maydis?
huitlacoche
what is a hypha (plural hyphae)?
greek for web, a thread-like structure
what is negative autotropism?
growth away from members of the same species (ex. germinating fungal spores)
what is autotropism?
growth towards other members of the same species during sexual reproduction
why is Harold Flor a genius?
he discovered that for every resistance gene (R gene) in the host there is a corresponding gene for avirulence (Avr gene) in the pathogen
how do we control downy mildew of grape?
host resistance, protective fungicides (Bordeaux Mixture), and systemic fungicides
what is the host and pathogen of stem rust of wheat?
host: wheat (Triticum aestivum) pathogen: Puccinia graminis
how does adherence work?
hyphae or another adhesion factor present. two types: nonspecific and specific.
what is a septae hyphae?
hyphae that have cross wall divisions within the hyphae
what is a coenocytic hyphae?
hyphae that have no cross wall, are hollow, and are multi-nucleate
what is the applied approach of studying plant pathology?
identification of the most effective control techniques with a focus on diagnosis, treatment, cure, and prevention of diseases
effect of wind on disease development
important for the spread of pathogen, wind carries spores over long distances. wind may also alter the rate of evaporation, influencing soil moisture.
what is Pseudomonas syringae?
important plant pathogenic bacteria that causes bacterial blight
what is Xanthomonas oryzae?
important plant pathogenic bacteria that causes bacterial blight of rice
what is Xanthomonas campestris pv. citri?
important plant pathogenic bacteria that causes citrus canker
what lessons were learned from the Irish potato famine?
imported crops and pathogens with limited genetic variation resulted in uniform susceptibility that was enhanced by vegetative propagation and a dependent population causing a conducive environment for late blight of potato and ultimately led to the potato famine
who is Thomas Burrill?
in 1882 he published a paper describing association of bacterium with fire blight of pear. it was later proven that bacterium caused fire blight disease by completing Koch's postulates.
what was the social impact of coffee rust?
in the 1600's coffee was a popular drink in England, but because of coffee rust destroying plantations, the English turned to tea.
how does oxygen affect plant growth?
inadequate oxygen can cause cell death e.g. blackheart of potato
how do growth regulators work?
increase auxin (cell elongation), required for tumor, gall, knot formation.
what negative impact did TMS have on corn plants?
introduced weakness into the plants and made them susceptible to race T of the fungus.
what is the problem with sterilizing soil in greenhouses for Pythium control?
it can kill beneficial antagonists
what was the result of Anton de Bary's potato experiment?
it proved that oomycetes can cause disease and was a major breakthrough for our understanding of how all diseases are transmitted.
what is the significance of fire blight of pear?
it was the first plant disease demonstrated to be caused by a bacterium using Koch's postulates!
how do parasitic plants disseminate viruses?
it's rare, but dodder is an example!
what is the significance of olive knot disease?
it's widely known for its remarkable biology because the bacterium grows intercellulary in plant tissues causing large quantities of auxin that lead to galls.
who is Anton de Bary?
known as the father of modern plant pathology for being the first to prove that Phytopthora infestans was responsible for potato late blight.
how does light affect plant growth?
lack of light prevents chlorophyll production and leads to etiolation (pale green seedlings)
what caused the Irish potato famine?
late blight of potato
what disease is caused by Septoria spp.?
leaf spots and blights of cereals and grasses
what is hypovirulence?
literally means "lesser virulence"
what is a biotroph?
live in "pretend harmony" pathogens that live within host tissues without causing death, evade detection and avoid elicitation of defense responses
what are fungi?
living organisms that do not have chlorophyll and cannot use energy from the sun to manufacture food, so they MUST obtain food from substrate
what are phytotoxins?
low molecular weight compounds produced by pathogens that are toxic to the plant host
what are secondary nutrients for nutrient deficiencies?
magnesium, calcium
what is a hemibiotroph?
majority of bacterial pathogens, can switch from biotroph to necrotroph and live in intracellular places
how is Striga controlled?
make use of a catch crop like cotton to suppress Striga, or fungus in the soil that can suppress the growth of the weed.
what is a disease?
malfunction or abnormality of host cells and tissues that results in irritation by a pathogenic agent or environmental factor and leads to symptoms that reduce the plants' value and cause deviation from its normal processes.
what is cutin?
primary component of the cuticle - waxy lipid layer covering the surface of a leaf/stem
what is the host of BYDV?
many grasses including wheat, barley, oats, etc.
how does seed transmission contribute to virus dissemination?
many plant viruses can be transmitted by seed, usually in the embryo, rarely on the seed surface
why is the pre-penetration phase critical?
many signals are communicated between the pathogen and the hosts. highly specific elicitor molecules induce formation of specific products in the host which may regulate growth or resist the pathogen.
effect of light on disease development
may promote or limit disease. generally, low light increases susceptibility to viruses and fungus.
what are the most infamous examples of new encounter diseases and who introduced them?
measles and chickenpox devastated American Indians when introduced from Europe
what are prokaryotes?
microscopic, unicellular human and animal pathogens, but some can affect plants
how does the environment affect germination and infection in Phytopthora infestans?
moist leaf surface is required for successful germination and infection
what is the most common cause of abiotic disease?
moisture!
how does recognition work?
molecular signals - plant phenolics, compounds released at wound sites interact with sensor in bacteria to activate virulence associated genes
how do pathogens disseminate?
most utilize the air, water, or some vector (including humans)
what is the slow phase of secondary cycle?
movement between adjacent cells occurs through plasmodesmata
what is chemotropism?
movement or growth towards chemicals or nutrients (ex. sugars in rhizosphere)
what are the methods of genetic variations in the absence of sex?
mutation and parasexual cycle
how are viruses disseminated via grafting?
natural root grafts and made-made grafts
whats the difference between polar flagella and peritrichous flagella?
polar are on one end, peritrichous surround the perimeter
what biological control methods are used on nematodes?
nematode trapping fungi can be used and are interesting but there is no reliable method of control of nematodes, predatory nematodes, bacteria, and endoparasitic fungi are other methods but also not very reliable
what are primary elements for nutrient deficiencies?
nitrogen, phosphorus, potassium
what is the major feature of prokaryotic cells?
no membrane bound nucleus - DNA floats freely throughout the cell
what kind of disease do abiotic pathogens cause?
non-infectious
how is BYDV transmitted?
not mechanically in nature nor in a lab, APHIDS are the species known to transmit the virus
what is horizontal resistance?
not race specific, moderate level of disease, generally involves several genes, expression of minor genes for R is less strong, difficult for pathogen to overcome, and influenced more by environment
what are the two basic components of a virus?
nucleic acid and protein
what are the characteristics of downy mildew?
obligate parasites that like moist cool conditions and require a film of water for germination and infection but only attack above ground parts of plants.
what is oedema?
occurs when soil moisture is too high and air surrounding leaves is cool and or very humid, roots absorb moisture faster than can be lost via transpiration
what is a autoecious rust?
one host in life cycle
define parasitism
one organism takes its nutrients from another and causes disease
why did genetic uniformity of potato crop contribute to the severity of the Irish potato famine?
only a few species of potato were collected in South America and from these, only pieces were taken back to Europe for propagation and potato seed pieces were used to plant the next years' potato crop BUT pathogens were able to survive the winter in stored potatoes, so infected potatoes were planted next season.
what are the two categories of virulence genes?
sensory and transfer mechanism
what is the perioxisome?
organelle in plant cells that is used for oxidation of fatty acids into energy for plant
define symbiont
organism involved in a symbiotic (mutual) relationship
define parasite/pathogen
organism that derives nourishment from another and in doing so causes disease
define saprophyte
organism that derives nutrients from dead organic matter
define facultative parasite
organism that is primarily a saprophyte but can be a parasite under the appropriate conditions
what is the host of Phytophthora parasitica?
ornamentals
what is the dormant stage of disease development?
overwintering or over-summering of pathogen occurs to allow them to survive during periods of poor growing conditions or environmental extremes.
describe the sexual stage of downy mildew:
overwinters as oospores which usually germinate directly and are resistant to adverse conditions.
what is the disease development of BYDV?
overwinters in perennial grass hosts (north) or annual grasses, fall cereals, and adult aphids (south). in the spring aphids acquire virus from infected hosts and spread the disease, in cold climates the inoculum can come from wind-borne, migrating aphids.
what is the disease development of TMV?
overwinters in stalks or soil, or manufactured tobacco products. primary inoculum in field via infected seed, man, and transplants. secondary inoculum via cultural practices
how does air pollution affect plant growth?
oxidants (ozone, NO2, and PAN), sulfur dioxide, and hydrogen fluoride cause damage
what is dwarf mistletoe?
parasitic plant that grows on pine trees and causes more damage to pine than any other disease or insect
what are broomrapes?
parasitize roots of plants like tomato and resemble small snapdragons but have no chlorophyll
what is horizontal resistance?
partial resistance to all races of a certain pathogen species. conferred by many genes that may be relatively ineffective by themselves but together are effective.
how do spores spread?
passive release vs. forcible discharge via wind or rain. often coincides with favorable conditions including periods when hosts are susceptible and environmental conditions are favorable for infection.
how is exclusion used to control nematodes?
pathogen free planting stock and quarantining
what are symptoms of bacterial canker of stone fruits?
pathogen produces syringomycin and many strains are ice nucleation-active (INA) causing frost injury to plants which ruptures plant cells.
what makes a successful pathogen?
pathogenesis genes and effectors allow the plant to evade the plant's defenses and survive and reproduce.
what is a local infection?
pathogens are limited to a small area of the body, ex. rust
why is site selection important for controlling fire blight of pear?
pear orchards are nearly impossible to establish in humid regions, so production is limited to western U.S.
what does Meloidogyne translate to?
pear shaped female
how do virulence factors relate to altered genetic control?
plant growth regulators
what is the disease theory of spontaneous generation?
plant, human, and animal disease occur spontaneously and are a punishment from God
what are PGIPs?
plant-produced polygalacturonase-inhibiting proteins interact with fungal polygalacturonase and inactivate the cell wall degrading enzymes but also prevent increase in the amount of oligogalacturonides.
how do virulence factors relate to interference with transport?
plugging substances
what is the host of Phytophthora infestans?
potato and tomato
what is pH?
power of hydrogen is a log function that ranges from 0 to 14 with numbers less than 7 being acidic and greater than 7 being alkaline
how are chemicals used to control nematodes?
preplanting with soil fumigants in greenhouses
what are sclerotinia diseases?
present in warm climates, cause damping-off, cankers, blight, and rots on vegetables, flowers, cereals, legumes, and weeds.
describe the disease progress of downy mildew of grape:
primary inoculum: overwintering oospore germinates to form a germ tube which immediately forms a sporangium that is dispersed by wind or water to the host. can overwinter as mycelium in dormant twigs. mycelium grows between cells and inserts haustoria into cells for feeding.
what is phylum Zygomycota?
produce non-motile asexual spores, have haploid hyphae and are coenocytic - they cause bread molds
what is microcyclic rust?
produce only two spore stages (teliospores and basidiospores)
what do avirulence genes do?
produce protein recognized as invasion signal as a major strategy to infect plants, uses a race specific elicitor
what is a secondary inoculum?
produced as a result of primary infection, produces secondary infections
what is a fungal mat?
produced between April and late June on red oaks that wilted during the previous summer. the mats are produced under the bark and attract vector insects.
what is translation?
production of protein from RNA
what is the term for one unit of inoculum?
propagule
what is a capsid or coat protein?
protein surrounding DNA or RNA - composed of many copies of a single protein
how is leafy mistletoe controlled?
pruning branches!
what does pectin methylesterase do?
removes methyl groups and improves degradation by other pectin degrading enzymes
what does pectin lyase do?
removes water and breaks pectin polymer chain
what is the scientific history of crown galls?
researchers demonstrated the requirement for wounding and suggested that crown gall is analogous to mammalian cancer, but found that crown gall tissue could grow autonomously without either the bacterium or the whole plant.
what is an example of a double strand RNA virus?
rice fiji disease virus
what is the structure of TMV?
rigid rod that is hollow and has a helical capsid
what are the different shapes of plant virus particles?
rigid rods, flexuous rods, and spherical
What is Olpidium?
root diseases and vectors for viruses
besides insect vectors, how else is DED spread?
root grafts - once a tree in a row is infected the disease can move through connected root system and kill the entire row
what does coffee rust do?
rust pustules on leafs can contain up to 150,000 spores and one leaf can have hundreds of pustules. rust reduces photosynthetic capacity and weakens tree, preventing the production of coffee.
types of plant pathogenic Basidiomycetes:
rusts, smuts, root and stem rots, and wood rotting fungi
what is the habitat of nematodes?
sandy soils in warm, moist climates
what is Meloidogyne spp.?
sedentary endoparasite that causes galls, stunting, and yellowing on a wide range of hosts
to what do we attribute the adaptability and genetic diversity of fungi?
sexual reproduction
how does DED reproduce?
sexual reproduction by ascospores is rare in the US because only one mating type is common, asexual reproduction by conidia usually occurs in one cycle per season
what are avirulence genes?
single gene in pathogen that triggers host resistance mechanisms and limits pathogens ability to cause disease on certain host genotypes
what are resistant genes?
single genes in host that allow recognition of certain pathogen genotypes
what is phylum myxomycota?
slime molds, "myxomycetes"
what is satellite RNA?
small RNA molecules that require a host virus for replication and modify disease symptoms
what are some vectors for Oak wilt?
small insects, mammals, and birds, but it is not very efficient
what are toxic minerals for plants?
sodium, salts, boron, manganese, copper, aluminum, and iron when high
what are some environmental factors that affect nematode populations?
soil composition, temperature, water status (movement and oxygen)
effect of moisture on black root rot of tobacco
some fungal spores require a film of water to germinate or require high humidity - higher soil moisture increases the severity of black root rot.
why does the degree of parasitism vary within parasitic higher plants?
some have chlorophyll and require only water and inorganic nutrients from their host while others lack chlorophyll and require sugar from their hosts.
how do nematodes feed?
some stay outside and use stylets to puncture cells inside the root (ring, stubby, root, and sting nematodes) while others enter and move throughout the root (lesion nematode) or stay in one feeding site (cyst and root-knot nematodes)
what is an example of an endoparasitic stem parasite?
southern california desert native Pilostyles thurberi or Thurber's stemsucker on a bush called Dalea
what is Heterodera glycines?
soybean cyst nematode - most damaging soybean pest that causes stunted plants, yellowing, and fewer nitrogen-fixing nodules
what is the host of Phytophthora megasperma?
soybeans
how does the environment affect dissemination in Phytopthora infestans?
sporangia are dispersed by air currents, and survival/distance spread is favored by moist conditions.
describe the asexual stage of downy mildew:
sporangia dispersed by water or wind can germinate directly in high temperatures via a germ tube or indirectly in low temperatures with zoospores
what are the effects of the environment on Phytophthora?
sporangia emerge in the morning and humidity causes sporangiophores to twist and eject the sporangia
what are signs of downy mildew?
sporangiophores emerge from stomata and bear sporangia which gives a white "downy" appearance to the underside of the leaf.
what are some symptoms of downy mildew?
sporangiophores turn brown/grey and branching pattern is distinctive and thus used for identification.
describe the lifecycle of Phytopthora infestans:
sporangium can either produce a germ tube above 68 degrees, or zoospores below 68 degrees
how are the spores of Cryphonectria parasitica disseminated?
spores are carried by wind and rain. also woodpeckers and insects can pick up the sticky conidia and ascospores.
what is an example of a cereal rust?
stem rust of wheat
what is barberry an alternate host for?
stem rust of wheat - rust is worse near barberry bushes
what is the basic approach of studying plant pathology?
study of diseased and resistant plants to determine the effects of disease and the nature of disease
what is a phytotoxin?
substance that is poisonous or toxic to plants
how does high temperature affect plant growth?
sunscald is common in fleshy fruits and vegetable and can inactivate enzymes or damage proteins
what did Tillet believe incorrectly?
that smut dust was poisonous
what is Rhizoctonia solani?
the Basidiomycete that causes damping-off, brown patch, stem, and root rot of vegetables, potato, cotton, rice, and many other hosts.
define disease resistance
the ability of a host plant to overcome the effects of a pathogen
define tolerance
the ability of a plant to survive the effects of a pathogen, despite the incidence of disease
what does the disease cycle refer to?
the appearance, development, and perpetuation of the disease as pathogen relates it to the host
how does citrus bacterial blast work?
the bacteria lives on host plants in cankers (primary source of inoculum) and isolates phytotoxin syringotoxin, the peptide acts on host cell membrane to form ion channels that result in electrolyte leakage and cause cell death and necrosis.
what group of pathogens is best represented by Family Peronosporaceae?
the downy mildews
what is cutinase?
the enzyme that degrades cutin - breaks polymer into monomers which actually induce the production of more cutinase.
why is ergot significant?
the fungus produces toxic alkaloids for humans
define susceptibility
the inability of a host plant to resist the effects of a pathogen
what is necessary for host indexing to occur?
the indicator plants must be inoculated with sap from the infected plant which is done by grinding leaves from the infected plant in a buffer and rubbing said buffer on indicator plants
what is inoculation?
the initial contact of a pathogen with a plant tissue where infection is possible
what is host indexing?
the mechanical inoculation of a set of indicator plants to observe which symptoms are induced on the species in order to tentatively ID the virus
how is dwarf mistletoe controlled?
the only way to control is to remove infected branches which usually means cutting down entire trees
what is Phytopthora infestans?
the oomycete that causes late blight of potato - this is a hemibiotroph
why is the lesion on plants infected with Xanthomonas campestris pv. campestris V-shaped?
the pathogen enters the host through hydathodes on the edge of cabbage leaves
what is dwarfing?
the size of the infected plant is almost always smaller than a healthy plant due to reduced photosynthesis
what is plant pathology?
the study of plant diseases, the organisms and factors that cause them, the mechanisms by which these are introduced, the interactions between disease causing agents and plants, and the methods to prevent or control diseases.
what is Olpidium brassicae?
the vector of lettuce big-vein virus, thick-walled spore stage that is virtually impossible to eradicate once established
what is Rafflesia arnoldii?
the world's largest flower that is parasitic and 3 feet in diameter
how does differentiation of infection structures work in fungi?
there are physical and chemical stimuli. powdery mildew and Magnaporthe grisea use appressoria. Rhizoctonia solani and Blumeria graminis secrete chemicals.
how is Chestnut blight controlled?
there is no effective control for trees in the forest, but hypovirulent strains of the same pathogen have been produced to slow infection
why do we see wilting in a field infested by nematodes?
there is secondary infection through plant wounds
what diseases are caused by phylum Plasmodiophoromycota?
these are obligate parasites that can cause hypertrophy and hyperplasia on roots and can serve as virus vectors - causes powdery scab of potato
what diseases are caused by phylum Myxomycota?
they are not normally causal agents of plant disease! they are saprophytes but they do not invade tissue and can be effectively controlled by fungicides
why are plasmids important?
they are the reason bacteria develop resistance to antibiotics.
why are antibiotics not widely applied as a control method for bacterial plant pathogens?
they can be expensive, but more importantly can create resistant bacterial strains that can be dangerous for humans
why is ergot still a problem for cattle?
they can't remove infected seeds
how do nematodes disseminate viruses?
they carry the virus non-propagatively and provide wounds for transmission
what is the difference between a mycoplasma and a virus?
they lack a cell wall and inhabit the phloem
what do hydathodes do?
they release extra water for the plant which make them a good area for bacteria to enter the host.
how do biotrophic pathogens avoid being detected?
they secrete molecules that are detected by resistance genes so they can live in "pretend harmony" , they have haustoria which remain outside plasma membrane to take nutrients
what was the importance of chestnut trees?
they were economically important for wood, food and natural products in the early 1900s. every 4th tree in the Appalachian forests was a chestnut.
how is citrus greening spread?
through insects called citrus pyslla
how does man disseminate viruses?
through mechanical transmission, i.e. tobacco mosaic virus
what are nematodes?
tiny, unsegmented worms that inhabit the soil and possess internal organs
what is the purpose of Koch's posulates?
to determine the causal agent of disease
what is an example of a (+) single strand RNA virus?
tobacco mosaic virus
what is an example of a (-) single strand RNA virus?
tomato spotted wilt virus
what is an example of a single strand DNA virus?
tomato yellow leaf curly virus
what are non-host specific toxins?
toxic to a range of plant species, some of which are not even hosts for a pathogen producing these toxins
what are mycotoxins?
toxic to humans and animals when they consume feed and food products contaminated with mycotoxigenic fungi
what are host specific toxins?
toxic to only one or few host species or even cultivars and no toxicity to other species/cultivars that are resistant to this pathogen
how do virulence factors relate to altered host metabolism?
toxins are host specific and non-host specific, plant growth regulators in plant pathogen interactions
what is T-DNA?
transfer DNA that contains genes for production of 2 classes of hormones (auxin and cytokinin)
what is Agrobacterium tumefaciens?
transfers genes for production of auxins, cytokinins, and opines and causes crown gall.
what is Ti plasmid?
tumor inducing plasmid, required for virulence
what is a heteroecious rust?
two hosts in life cycle
what is macrocyclic rust?
typically produces all 5 spore types (teliospoes, basidiospores, spermatia, aecia, uredospores)
what is a polycyclic pathogen?
under optimal conditions of temperature and moisture, multiple generations may occur
what are immunoassays?
use of antibodies for specific binding and identification method
what is electron microscopy?
uses electron stains to show the topographical features of a virus, infected host tissues are revealed
what is biological control of bacterial plant pathogens?
using one bacterial organism to control another
what is yellowing?
usually caused by viruses that are phloem limited and infection disrupts transportation of water throughout vascular tissue
what was Flor's experimental set up?
variety ottawa 770B was susceptible to race 22 but resistant to race 24. variety bombay was susceptible to race 24 but resistant to race 22 so he used Mendelian genetics to conclude that a single gene is responsible for resistance/susceptibility
how is BYDV controlled?
vector control is ineffective, host resistance varieties with reduced susceptibility are available
how does Rhizoctonia solani reproduce if not by spores?
vegetatively - it exists primarily as vegetative mycelium and/or sclerotia
what are some sources of air pollutants?
vehicles, power stations, smelters, industrial plants, and more
how do fungi disseminate viruses?
very few viruses transmitted by zoospores or resting spores of lower fungi
what are satellite viruses?
very small defective viruses that multiply by association with a helper virus that complements the defective virus and encode their own coat protein
what is an example of a host-specific toxin?
victoria blight of oats - necrotrophic pathogen that induces programmed cell death in oat variety Victoria
what is the economic importance of viruses?
viruses attack all forms of life and in agriculture can cause reduced yield/quality of plants
how does the environment affect spore development in Phytopthora infestans?
warm weather (>68 degrees) leads to direct germination of the sporangium. cool weather (<68 degrees) allows for the formation of zoospores which give 8X the number of infectious spores.
where is damping-off disease often a problem?
water-saturated soils
why is ergot of wheat and rye not a problem anymore?
we have modern seed cleaning methods that remove ergots from grain before it's milled or used for animals
when does the most serious damage occur in rice bacterial blight?
when the bacterium attacks the nodes just below the head, prevents the flow of nutrients to the kernels and they will stop developing
what is a negative stain?
when the electron dense stains do not react with the virus, but penetrates available space on the surface surrounding the virus
what is the infection stage?
when the pathogen establishes contact with the susceptible cells and tissues and procures nutrients from them
define commensalism
when two organisms live together and one benefits while the other is unaffected
what is the distribution of corn smut?
wherever corn is grown but most serious in warm/dry areas
what is an example of a non-host specific toxin?
wildfire disease of tobacco - inhibits glutamine synthetase enzyme that blocks synthesis of glutamine and builds up toxic levels of ammonia within the cells
how does low humidity affect plants?
wilting, drought causes death
define race/strain
within each special form (pathovar) some races/strains may attack some varieties of the host plant but not others depending on genetic makeup
what does exopolygalacturonase do?
yields monomers that can be used as a food source
what does endopolygalacturonase do?
yields oligomers, gives a rapid reduction in structural integrity
how does contract or attraction work?
zoospores (Pythium spp.) are attracted by root-derived exudates and motile bacterial cells are attached to plant exudates?
how many genes does the average fungus have?
~10,000-12,000
what are the host plants of Verticillium spp.?
~200 species of hosts: annual vegetables, flowers, crop plants, weeds, major problem for cotton, potato, eggplant, and tomato