Plpa Exam 2 (fungi)

Kingdom Protozoa

- (Single-celled eukaryotes, includes some algae and protozoa, such as amoebae and paramecia). - Phylum: Myxomycota (Slime molds) "Myxomycetes" • grow superficially over the plant when there is a lot of moisture - Phylum: Plasmodiophoromycota "Plasmodiophoromycetes" • Example: Plasmodiophora brassicae (disease: club root of crucifers).

sporophore

Spore bearing structure - Ex) conidium on conidiophore

sporocarp or fruiting body

Spore producing body

Canker

Sunken lesion on the branch, trunk or stem. Phloem is killed and translocation of nutrients is cut off.

Ascomycetes characteristics*

The "Sac fungi" 1. Haploid vegetative hyphae. 2. Septate hyphae. 3. Chitin in cell wall. 4. Sexual stage. Produce sexual spores, called ASCOSPORES. These are born in a zygote structure, called an ASCUS (literally means a "sac" in Latin). • 8 ascospores in each sac

Diseases caused by different groups of fungi: Kingdom Chromista

Unicellular or multicellular, includes brown algae, single-celled "phyto"-plankton, and oomycetes. Phylum: Oomycota ("egg-like" mycelium). - multinucleate, coenocytic (no cross wall) mycelium - diploid oospore in oogonium - zoospore in zoosporangium 1. Pythium spp.: "damping-off" 2. Phytophthora infestans: Late blight of potato and tomato 3. Downy mildews: Obligate parasites • dicots = Bremia, Peronospora, Plasmopara, • monocots = Peronosclerospora, Sclerophthora, Sclerospora

4 major characteristics of oomycete

a. Diploid vegetative hyphae. b. Multinucleate, coenocytic hyphae (no cross walls). c. Glucans in cell wall. d. Sexual cycle.

Fungal growth: Branched hyphae

as hyphae grow they branch

anamorph

asexual stage in Ascomycota or Ascomycetes

two types of hyphae

coenocytic: no cross wall; hollow, multi-nucleate hypha Septum (plural: septae): cross wall; divisions within hyphae

mycelium

collection of hyphae (the vegetative body)

Aspergillus flavus: conidiophore and conidia

electron scanning micrograph "one microtoxin that is strictly controlled

what is a fungus

eukaryotic heterotrophic, absorptive organisms that develop a rather diffuse, branched, tubular body and reproduce by means of spores

why are fungi not as problematic at fighting

fungi are more complex and the more complex you are the more vulnerable

What gene would be want to over express to conquer the pathogen if it was in the kingdom fungi?*

glutinases and chitinases

fungal physical organization

have: vacuoles, ribosomes, nucleus, plasma membrane, lipid bodies (basidiomycetes are dichariotic meaning they need to have two nuclei)

heterothallic vs homothallic fungi (in phytophthora)

heterothallic: female and male organs are on different strians homothallic: female and male organs are on the same strain

heterotrophic

organisms that obtain their food from something else rather than creating it

Fungal growth: Budding

production of small outgrowth (bud) from parental cell. The nucleus of the parental cell divides and one daughter nucleus migrates to the bud - how yeast grows

teleomorph

sexual stage in Ascomycota or Ascomycetes

3 ways in which fungi reproduce

sexual, asexual, and para-sexual

hyphae

thread/web like structure - 2 types of

Dutch Elm Disease (DED)

A. Most destructive shade tree disease in the U.S. - Dutch elm disease (DED) is a deadly fungus that can kill an elm in as little as three weeks by clogging its water-conducting vessels. - Symptoms: As early as June the leaves on an infected tree will wilt, turn yellow, then curl and turn brown - Note: normally the youngest branches are infected, normally infected by beetles that tend to feed on sap from the youngest branches and they act as vectors for the pathogen - initial symptoms include wilting and chlorosis of affected branches above the point of infection (so-called flagging) B. Attacks all American and European Elms. C. Once a tree is infected by DED it needs to be removed and disposed of properly by burning it. - Pathogen: Ceratocystis ulmi - Hosts: American elm (Ulmus americana) is the most seriously affected of all elms while the Siberian elm (Ulmus pumila) also called Chinese elm is tolerant but not immune to the disease Reproduction of DED: - Sexual Reproduction by ascospores • Sexual reproduction is rare in the U.S. because only one mating type is common. • Heterothallic: needs two mating types for sexual reproduction. • Ascocarp = perithecium. (Cont.) - Asexual Reproduction by conidia • Usually only one cycle per season, or limited secondary spread Transmission of DED: 1. Insect Vectors (beetles) a. European Elm Beetle b. Native Elm Bark Beetle • can fly up to two kilometers as it searches for healthy elms to feed on. The DED fungus has sticky spores that become attached to the beetle during its breeding period. The beetle then spreads the fungus when it feeds on and over-winters in healthy elms • Because female makes egg chamber in wood of dead and dying trees, this is particularly a problem in wood piles. • Because the beetle feeds on young tissue, an early symptom is the flagging or wilting of small branches. • major control measure is to control the beetles but its nearly impossible 2. Root grafts - Roots of different trees can graft together and establish vascular connections. - Conidia in xylem can then move from tree to tree in the transpiration stream. • once a tree in a row is infected it will cause death in all the trees that are connected through the root system, important transition mode for DED Control of DED: 1. Eradication - Sanitation: removing breeding sites for the beetle: (a) dead logs and (b) infected trees. (c) In some areas, storing elm logs is illegal. 2. Protection Control the beetle vector. Insecticides have not proven very useful. Long-distance spread of inoculum by beetle further complicates control. 3. Host Resistance Asiatic variates have resistance 4. Therapy with systemic fungicides • ex. Benomyl: injected into tree or sprayed on leaves. Injection is more effective, but also more costly. This only works early in the infection process

Diseases caused by different groups of fungi: Kingdom Protoza

A. Phylum Myxomycota: "The Slime Molds" - Not normally causal agents of plant disease, (don't colonize the tissues they just superficially grow on the stems (it only hurts the plant when there is so much that it prevents photosynthesis) - Saprophytes: live on decaying material - Grow on plant surfaces during periods of warm, wet weather. - Do not invade the tissue. - Primarily an aesthetic problem. If too dense, they can block sunlight, and limit photosynthesis. - are effectively controlled by certain fungicides • slime mold - Physarum cinereum B. Phylum Plasmodiophoromycota: Plasmodium (no hyphae) - Zoospores. - They can cause severe losses. - All obligate parasites (cannot live outside host, biotrophs). - Extremely widespread in soils. - Can overwinter as diploid "resting spores"- zoosporangia that germinate to form zoospores. - Cause hypertrophy and hyperplasia club-shaped swellings on roots. - Also serve as virus vectors. Examples - Club Root of Cabbage: - Pathogen: Plasmodiophora brassicae • symptoms: Fist sized galls, stunting, eventual yellowing - Powdery Scab of potato: Spongospora subterranea, vector for potato mop-top virus • symptoms: causes the formation of superficial pustules that release spores into the soil

Parasexual cycle

- A sequence involving heterokaryon formation, diploidization, and haploidization, often resulting in the formation of recombinant nuclei. - Unlike the sexual cycle, the parasexual cycle can occur at any point or continuously throughout the life cycle. - in order for sexual reproduction to occur there must be two different strains of the fungi that recombine (homologous chromosomes) and make a new strain HOWEVER if not through sexual reproduce (meiosis) when two hyphae grow in close proximity to each other they can fuse (heterokaryon- nucleus from one strain and the nucleus of another combine) transferring genetic material - Despite the fact that some fungi lack a known sexual cycle, they are amazingly adaptable and diverse. Therefore, there must be a mechanism for increasing variation. The source of some of this variation is the parasexual cycle and mitotic recombination. • Examples - Fusarium and Verticillium Both of these fungi were considered deuteromycetes (no sexual cycle), but plant breeders are continually frustrated by the appearance of new genetic variants (races) - one mechanism for this variation is parasexualism.

Fungal growth: Apical elongation

- Fungal growth occurs at the tip of hyphae = apical elongation. - Most of the new cell wall material is deposited in the terminal 1 mm of the hypha: the "apical dome" - can only grow longitudinally but not radially like trees which increase in diameter

fungal metabolism

- Fungi prefer moist habitats and temperatures between 15°C and 35°C. - The carbon needs of fungi for energy metabolism and biosynthesis has to be met heterotrophically by one of three lifestyles: 1. parasitism of plants or animals (causing disease). 2. saprophytism, growing on dead animal, plant or microbial biomass. 3. symbiosis, growing together with algae, plants or insects.

Fungal taxonomy (historical)

A) - historically was based primarily on reproductive structures. - The morphology of the spores and sporocarps (= a general term for a multicellular body or organ that contains or bears spores). • Sometimes sterile structures of life cycle characteristics are used. • Any taxonomic scheme is imperfect, and recent advances in DNA technology have caused enormous changes. B) - Note, historically fungi were divided into the "lower" fungi vs. the "higher" fungi. • Lower fungi are those with no mycelium (have plasmodium) or those that rely on free water for completion of the life cycle. • Higher fungi are those that have a true mycelium, have non- motile gametes and more highly organized structures.

spores reproduction style

Asexual - sporangia - zoospores Sexual - ascospores - basidiospores - zygospores - oospores

Fungal Physical Organization

Basic unit = hypha (plural: hyphae). Greek for "web", a thread-like structure.collection of hyphae = mycelium: vegetative body. Two types of hyphae:Coenocytic = no cross wall; hollow, multi-nucleate hypha. Septum (pl: septae) = cross wall divisions within hyphae.

Basidiomycetes: Corn Smut*

Most important pathogen in India - Host: Corn (particularly sweet corn). - Pathogen: Ustilago maydis - Distribution: wherever corn is grown, but most serious in warm and moderately dry areas. - Symptoms: • Causes galls (overgrowths) on host plant. • Hyperplasia (increased cell division). and Hypertrophy (cell enlargement) • Galls can form on any of the above ground part of the plant; it can destroy ears and reduce yield. • Severity: can be locally severe (individual fields), but in total about 2% annually. - Lifecycle: - Most smut fungi produce only teliospores (is an asexual spore: do not infect directly they give rise to basisiospores which are the ones that infect the plant thus continuing the cycle of the pathogen) and basidiospores (are the sexual spores) (note difference with wheat rusts). - Basidiospores germinate, and a limited haploid mycelium develops. - Haploid mycelium has limited pathogenic potential, and fusion with another haploid hyphae is required for infection to continue. - Dikaryotic mycelium initially grows intercellularly, but eventually invades the host cells and replaces them with black teliospores. - Characteristic symptoms involve invasion of the developing kernel, where teliospores form. -Teliospores give rise to basidiospores and keep the cycle going

Main groups of plant pathogenic oomycetes and fungi (don't confuse with classification)

Oomycetes Characteristics - Produce 2 types of asexual spores (sporangia and zoospores). a. Diploid vegetative hyphae. b. Multinucleate, coenocytic hyphae (no cross walls). c. Glucans in cell wall. d. Sexual cycle. Ascomycetes Characteristics* - Produce 8 sexual spores (ascospores) in a zygote called an ascus. a. Haploid vegetative hyphae. b. Septate hyphae. c. Chitin in cell wall. d. Undergo sexual cycle. Basidiomycetes Characteristics - (sexual spores (basidiospores) produced on the outside of the zygote called a basidium). a. Dikaryotic vegetative hyphae. b. Septate hyphae. c. Chitin in cell wall. d. Sexual cycle: Haploid spores produce a limited haploid mycelium. Two haploid hyphae fuse (plasmogamy) to yield the dikaryotic vegetative state.

Oomycetes vs Ascomycetes

Oomycetes: a. Diploid vegetative hyphae. b. Multinucleate, coenocytic hyphae (no cross walls). c. Glucans in cell wall. d. Sexual cycle. Ascomycetes a. Haploid vegetative hyphae. b. Septate hyphae. c. Chitin in cell wall. d. Undergo sexual cycle.

Fungal reproduction: sexual spores

Sexual spores (meiospores): 1. Ascospores (Ascomycetes) 2. Oospores (Oomycetes) 3. Zygospores (Zygomycetes) 4. Basidiospores (Basidiomycetes)

Whats the difference and similarities of oomycetes?*

Similarities: - cell wall is composed of glucan and small amount of cellulose - diploid hyphae (2n) - Coenocytic (no cross wall) - zoospores (asexual) are produced in zoosporangium - oospore (sexual) are in oogonium - all produce zoospores (weird way of penetration due to 68˚) Differences: - Pythium spp (damping-off): necrotroph • infect anything below ground - Phytophthora infestans (late blight of potato, tomato): Hemibiotroph • infect every part of the plant - Downy mildews (obligate parasites) - can not be cultured in Koch's postulates • downy mildew of grapes • blue mold (downy mildew) of tobacco • downy mildew of lettuce Biotroph • infect anything above ground

The Downy mildews: latest disease outbreaks

1. Blue mold of tobacco: 1979, Cuba, destroyed almost entire tobacco industry - Peronospora tabacina. 2. Downy mildew of sorghum: Frequent outbreaks in Texas - Peronosclerospora sorghi. 3. Downy mildew of roses: recent losses to Texas nurseries - Peronospora sparasa

Kingdom Fungi

- Have mycelium, and cell walls contain glucans and chitin. Lack chloroplasts. Phylum Chytridiomycota: produce zoospores with single posterior flagellum. (haploid hyphae (N) and coenocytic). • Olpidium brassicae: vectors viruses (pathogen itself isn't a big deal but the fact that it vector viruses is. If a fungus is a vector its biotrophic) Phylum Zygomycota: Produce non-motile asexual spores; (haploid hyphae (N) and coenocytic). • Zygomycetes cause bread molds. • Examples (both are zymomycetes): > Rhizopus: º bread mold. º soft rot of fruits and vegetables. > Glomales (includes several genera): º Mycorrhizal fungi: symbiotic partners on roots of many plants. Phylum Ascomycota: "Ascomycetes": the sac fungi. - Most have a sexual stage (teleomorph) and an asexual stage (anamorph). - Sexual spores: ascospores, generally in groups of eight within an ascus (means a "sac"). - Asexual spores: conidia form either on free hyphae or in asexual fruiting bodies (e.g., pycnidia). • there are some ascomycetes that are asexual spores that are not conidia - Neurospora is a model research organism. Major to understand human medical and plant patgogens 1. Perithecial fungi (Pyrenomycetes) • Asci in closed bodies (cleistothecia) or with an opening (perithecia). • Examples: > Erysiphae graminis (powdery mildews of wheat). > Endothia parasitica (chestnut blight). > Claviceps purpurea (ergot of wheat and rye). - Classified based on the ascocarp types. 2. Pseudothecial fungi (Loculoascomycetes) • Asci in cavities ("locules") within a mycelial matt ("stroma"). Stroma with a single cavity is called a pseudothecium. (fungal body that sits out of the tissue of the plant) Examples: > Cochliobolus heterostrophus: Southern Corn Leaf Blight > Gaeumannomyces graminis: "take-all" disease of wheat and turf grass. > Venturia inaequalis: apple scab. 3. Apothecial or Cap fungi (Discomycetes) • Asci are contained on fruiting structures (ascocarps) shaped like cups or cushions called apothecia. • Example: Sclerotinia, a classical necrotroph 4. Imperfect or asexual fungi (Deuteromycetes) - NOT ANYLONGER AN ACCEPTED CLASSIFICATION • Sexual reproduction lacking or unknown. • Examples: > Alternaria: root and storage rots. > Penicillium > Phymatotrichum omnivorum: root rot of cotton and other plants. • Some have no sexual or asexual stage known > Rhizoctonia: root rots, seedling diseases. Phylum Basidiomycota (club fungi): - rust, smut, and bunt fungi wood decay and root rot fungi • Examples: > Puccinia spp.: Cereal Rusts > Ustilago maydis: Corn smut > Armillaria: root rots of forest and fruit trees

Pythium: Damping-off

- Kingdom Chromista, - Phylum Oomycota - 2 primary genera: • Pythium • Phytophthora - Important: Other genera can cause a damping-off-like disease, including many ascomycetes such as Rhizoctonia and Fusarium and Septoria. - Primarily a seeding disease - Affects roots and plant parts in contact with soil, i.e., tubers, seeds, lower stems, etc • can infect any plant part that is in contact with soil normally roots though. • typically not a problem for mature plants normally targets young plpnts . - Pre-emergence: Seedlings die before they emerge...both pre- and post-germination. - Post-emergence: Plants can also die after they emerge. - More mature plants are generally not killed by these pathogens, perhaps due to increased reinforcement of the cell walls by lignin which the pathogen cannot degrade, but root and stem lesions can severely limit growth and productivity. - Often a problem in water-saturated soils, where seedling growth is retarded.

Phytophthora: Host resistance

- Monogenic resistance is present in some non-cultivated varieties and wild relatives. For example, Solanum demissum. - Solanum tuberosum = cultivated variety. • The fungus develops new races and overcomes single gene resistance rapidly. Also called "vertical resistance". • Seeking plants with a stable source of moderate level of horizontal resistance is another approach. Also called field resistance. - Vertical resistance: Complete resistance to certain races of a pathogen. Usually (perhaps always) single gene resistance. • Not dependent on environment its either resistant or it is not - 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: sometimes called minor gene resistance. • instead of 100% resistance they are 60% resistance. Effective against multiple strands and is impossible to break for pathogen (can't evolve multiple strands that are capable of overtaking so many resistant genes) • strongly dependent on environment

Sexual reproduction: Types of Ascocarps in the Ascomycetes*

- Naked asci: sit on top of hyphae with 8 ascospores - Cleistothecium: a whole bunch of asci that contain 8 ascospores that does not have an opening - Perthecium: specialized organ is buried in the organism with an opening that contains a bunch of asci with 8 ascospores - Apothecium: asci (8 spores) site in a cup like shape

The downy mildews: Characteristics

- Pathogen family: Peronosporaceae - Host: Most cultivated grains and vegetables, ornamentals, and many field crops. - Green island phenomenon: green areas of the lead are actually the areas where the pathogen is located and can even persist after the leaf has fallen off of the tree (make the leaf continue to photosynthesize even though they have no incoming form of nutrients) - Characteristics: 1. Obligate parasites AND Biotroph (no saprophytic stage; contrasts with Pythium which is primarily a saprophyte and causes damping-off). • rust, downy mildew, and powdery mildew are all obligate parasites • Hyphae grow between cells (intercellularly) and insert feeding structures (haustoria) into cells (how they keep the green islands alive by "injecting proteins and transcription factors" 2. Moist, cool conditions (like other Oomycetes) are a primary determinant of disease severity. Require a film of water for germination and infection, and high humidity. 3. Attacks above ground parts of plants. Primarily cause foliage blights, attacking young tissue. • one of the major differences between pythium, phytophthora, and downy mildew is the areas of the plant which they infect: downy mildew infects areas above ground (new tisssue) 5. Asexual stage: sporangia dispersed by water or wind, can germinate directly (high temps) via a germ tube, or indirectly (low temps) to give zoospores (just like Phytophthora). 6. Sexual stage: Overwinters as oospores which usually germinate directly, and are resistant to adverse conditions. Each growing season ends with sexual reproduction, ensuring genetic variation. 7. Limited host range for each species (contrasts with Pythium). 8. Like other Oomycetes, its vegetative state is diploid.

Phytophthora: pathogens and hosts

- Pathogen: Phytophthora infestans - Host(s): potato and tomato - Pathogen: Phytophthora megasperma - Host(s): soybeans - Pathogen: Phytophthora parasitica - Host(s): ornamentals - Pathogen: Phytophthora citrophora - Host(s): citrus

Phytophthora: Sudden Oak Death

- Pathogen: Phytophthora ramorum

Basidiomycetes: Root and Stem rots

- Rhizoctonia and Sclerotium known as the "Sterile Fungi"; thought only to produce sclerotia and incapable of producing other spores. Now known to have a sexual cycle but it is rare. - Rhizoctonia solani, damping-off, brown patch, stem and root rot of vegetables, potato, cotton, rice and many other host. Rhizoctonia solani: the most widely recognized species of Rhizoctonia - Rhizoctonia solani is a basidiomycete fungus that does not produce any asexual spores and only occasionally will the fungus produce sexual spores (basidiospores). - In nature, R. solani reproduces vegetatively and exists primarily as vegetative mycelium and/or sclerotia. - Brown patch - Significant Texas turf disease: St. Augustine (warm season grass) Brown patch Control * 1. Do not over fertilize w/ N, especially in autumn when grasses going dormant. 2. Good surface drainage - (for most turf diseases do not water at night in summer). 3. Keep thatch less than 2 cm thick. 4. Fungicides effective. Sclerotinia Diseases: - Primarily a disease of warm climates - Cause a damping-off of seedlings, stem canker, crown blight and root, bulb and fruit rots. - Large host range: vegetables, flowers, cereals, legumes and some weeds. - Signs/ Symptoms: • Cottony white mass of mycelium in and on infected tissue sclerotia- small round uniform - dark brown. - Control, Difficult to control: • Crop rotation • Deep plowing-expensive • Fumigation • Biocontrol

Phytophthora: sexual cycle

- Similar to that for Pythium. • Forms oogonia (female organs) and antheridia (male organs). • The antheridium fertilizes the oogonia and leads to the diploid oospore (zygote). - The fungus is heterothallic (female and male organs are on different strains). Note difference with homothallic fungi. a. Both mating types are now present in the U.S. and in Europe b. In S. America and Mexico where the fungus is native, both mating types are present, and sexual reproduction is common Note: the US didn't care about Phytophthora until aftera new mating type was introduced (heterothallic, which produced a different strand that was resistant to chemical fungicides)

Disease cycle of Phytophthora infestans (late blight of tomato and potato)* (LIFECYCLE)

- Sporangium can either infect through direct or indirect germination based on the temperature • Direct germination > If its over 68˚F than direct germination will occur with the sporangium producing a germ tube "apressoria" that will then infect a plant using brute force. • Indirect germination > occurs when the temperature is less than 68˚F and the sporangium then releases 8 asexual zoospores which result in 8x the number of infection sites. - Next the infected plant can either: 1. Have sporulation on the leaf that results to more sporangium 2. Have sporulation from young plants in the spring that results in more sporangium 3. Have sexual reproduction (can only occur when both mating types are present) • antheridium and oogonium combine to create the oospore (sexual spore) which then becomes sporangium which can now either germinate directly or indirectly depending on the temperature.

Role of fungi

- The Kingdom Fungi includes some of the most important organisms, both in terms of their ecological and economic roles. - By breaking down dead organic material, they continue the cycle of nutrients through ecosystems. - In addition, most vascular plants could not grow without the symbiotic fungi, or mycorrhizae, that inhabit their roots and supply essential nutrients. - Other fungi provide numerous drugs (such as penicillin and other antibiotics), foods like mushrooms, truffles and morels, and the bubbles in bread, champagne, and alcohol in beer, etc.

Fungal taxonomy (now)*

- The new fungal taxonomy is based on phylogenetic relationships derived from DNA sequence information. - "Fungi" are now divided into three Kingdoms, only one of which are considered "Fungi". - Kingdom: Protozoa • Phylum: Myxomycota • Phylum: Plasmodiophoromycota - Kingdom: Chromista • Phylum: Oomycota Kingdom: Fungi • Phylum: Chytridiomycota • Phylum: Zygomycota • Phylum: Ascomycota • Phylum: Basidiomycota

Fungal reproduction

- asexual reproduction - sexual reproduction - Genetic variation in the absence of sex

Fungal reproduction: Sexual reproduction

- meiosis, harder to control - Meiosis involves recombination between homologous chromosomes and is a key mechanism for increasing species diversity. - Sexual stage can allow for: 1. Increased survival in cold climates. Sexual spores are frequently tolerant of adverse conditions. 2. Increased genetic diversity of individuals. - Therefore, more variation for selection: • Developing fungicide resistance. • Overcoming disease resistance.

Asexual reproduction

- mitosis, easier to control - The haploid, diploid or dikaryotic state can be maintained by mitotic divisions. - During mitosis DNA is replicated and cell divided, and faithfully maintains the genotype of the parental cell. • can not gain a resistance to a fungicide because they can not mutate or evolve bc they are identical - Imperfect or Anamorph - the massive reproduction potential of most fungi is associated with their asexual stage. • vegetative hyphae (can be haploid, diploid, or dikaryotic). • asexual spores are produced by mitotic cell divisions.

What do you need to know about your enemy to be able to come up with a strategy to control the disease?* final test qestion

- what is its lifecycle (hemibiotroph, biotroph, or necrotroph) - if its hemibiotroph or biotroph it most likely has resistant genes against it and therefore can be targeted.

Canker diseases of trees caused by Ascomycetes: Chestnut Blight

-Pathogen: Cryphonectria parasitica - New encounter disease • Pathogen was introduced along with Asiatic Chestnut varieties in NY from Asia- the farther away from the place of origin the less resistance you will find Significance and losses: 1. Destroyed 30 million acres of the American Chestnut. 2. Chestnut was economically important for wood, food and natural products. • Early 1900's. Perhaps every fourth tree in the Appalachian forests was a chestnut. It was important for: > rot-resistant wood > food for humans and animals > tannins in the tanning industry. 3. Over a 40-year period, the chestnut population was devastated. - Infection occurs through wounds and fungus grows in phloem and cambium of the tree. • plants often respond too late - Toxin is produced that diffuses into xylem. The plant reacts by producing gums and this blocks water transport (transpiration) and causes a wilt. Dissemination: - Spores are carried by wind and rain. Also woodpeckers and insects can pick-up the sticky conidia and ascospores. - *The ability to spread over long distances on wildlife made quarantines ineffective. - Sexual stage: • Perithecia of Cryphonectria parasitica in a stroma. The perithecia contain many asci with 8 ascospores each. • The ascospores are forcibly ejected and carried in air currents. Control: - Presently there is no effective, practical control for trees in the forest. On an individual tree basis, pruning of infected branches and trees can help. - Biocontrol: • Develop hypovirulent strains of the same pathogen. • Hypo-virulence: literally means "lesser virulence". • Soon after epidemics began in European chestnuts, it was observed in Italy and France that some cankers spontaneously slowed down or stopped. > American Chestnuts that were infected BUT didn't die had a single stranded RNA that was acting as a disease of the fungus: this caused the spreading of the fungus to slow down, and give the chestnut time to react to the fungus in time • Experiments showed that the trees involved were no more resistant than other trees.

fungal growth

1) Occurs at tip = apical elongation 2) Follow different types of directional growth = tropisms 3) Branched hyphae 4) Budding (e.g. yeast)

5 sections of fungi

1) Physical organization (hypha, mycelium, coenocytic, septum). 2) Fungal growth (directional growth at the tip, chemotropism, autotropism, thigmotropism). 3) Fungal reproduction: (sexual, asexual and para-sexual). 4) Taxonomy of fungi. 5) Main groups of plant pathogenic fungi.

Fungal growth: types of directional growth = tropisms

1. Chemotropism: movement towards chemicals (nutrients), for example, in the rhizosphere (sugars etc.). - ex) fungi in soil how do you tell where the plant is and when its time to germinate? They are attracted to exuding sugars of the plant into the soil (30%) they do this to attract symbiotic organisms to the plant. 2. Autotropism: growth towards other members of the same species. "Negative autotropism": growth away from members of the same species, for example, germinating fungal spores. - positive autotropism is towards each other (produce sexually) - negative autotropism is when they grow away 3. Thigmotropism: growth directed by touch. Contact-sensing or thigmotropism is the directional growth response of cells in relation to topographical guidance cues. - Certain fungi align themselves on plant surfaces according to "touch" or contact stimuli. Due to sense of touch they grow along grooves or through natural openings such as stomata. - Thigmotropism is thought to play a major role in the location of infectable sites on plants by fungi and has recently been shown to be a property of human pathogens. - Ex 1) Stomates in grasses are arranged in rows. Germ tube of certain rust fungi grows perpendicular to these rows, thereby increasing the likelihood of encountering a stomate for entrance into the leaf. - Ex 2) Stomate structure can induce infection structures (appresorium) in certain fungi. Physical replicas of the leaf surface can mimic this effect. - However, in other fungi, the developmental change is induced by chemical elicitors (often volatiles), or by the hydrophobic nature of the leaf surface. Often, it is a combination of the two (chemical + physical).

Pythium: control (how do you control damping-off disease)

1. Fungicides a. Seed treatments can let the plant get past the susceptible seedling stage. (seeds are precoated with fungicides to ward off pythium, phytophthora, and others that cause damping off disease) b. Systemic fungicides. 2. Host Resistance: Limited success with resistant cultivars. 3. Sterilizing soil in the greenhouse: Problem - may kill beneficial antagonists. 4. Avoidance via site selection: Good soil drainage. 5. Crop rotation to keep down fungal population. However, oospores are long-lived. • not very effective bc: pythium has a wide range of hosts so its hard to rotate crop to a resistant crop, and when oomycetes produce sexually (oospores) is not easily degraded by extreme weather conditions 6. Plant shallow for quick emergence. • don't plant anything too deep bc it makes it harder for the seed to emerge. 7. Avoid overfertilizing with nitrate fertilizers. 8. Biocontrol with antagonistic fungi or bacteria.

Fungal reproduction: Genetic variation in the absence of sex (no sex)

1. Mutation: millions of spores per day, even at a low mutation rate you can get new genotypes (leads to genetic variation). 2. Parasexual cycle.

Phytophthora: effects of environment on Phytophthora

1. Sporangia emerge from the stomates in the morning. Wind and changes in humidity cause the sporangiophores to twist and eject the sporangia. • sporangia is a wimpy structure (won't survive for more than 6 hours if the environment is not conducive for it, oospores last for years) 2. Moist air is required for survival of the airborne inoculum. 3. Sporangia land on leaf surface, which must be moist: Survival is 3 to 6 hrs at high R.H.'s and temps below 80°C. Germination: a. Indirect: 10-18°C (0.5 - 2.0 hrs). Multiple zoospores. Eight zoospores per each sporangia. b. Direct: 18-25°C. Single germ tube. Penetration is via an aspersorium and penetration peg; 2 to 2.5 hrs at 15 to 25°C. • aspersorium breaks through the cell wall from brute pressure

The Downy Mildews: Symptoms and Signs

1. Sporangiophores emerge from stomata (mostly on lower side of leaf), and bear sporangia. - This gives a white, "downy" appearance to the underside of the leaf. 2. Sporangiophores later turn brown/grey. 3. Branching pattern of the sporangiophores is distinctive for each genus, and is used for identification. • morphology of sporangiophores are very unique to different downy mildews

Pythium: Environmental effects on Pythium

1. Temperature: - High temps (above 18˚C (68˚F) give direct oospore or sporangia germination (production of germ tube) (direct germination). - Low temps (between 10 and 18oC)give indirect germination via production of motile zoospores. Disease is favored by temps that are non-optimal for plant growth. At optimal temperatures the plant may outgrow the pathogen. 2. Moisture - Required for motile zoospores to infect the host. - Anaerobic conditions can cause stress in the host plant, and limit the extent of cell wall fortifications. 3. Nutrition - Excess nitrogen in soil favors disease.

Fungal reproduction: Asexual spores

1. Zoospores: produced by Phytophthora infestans 2. Conidia (singular: conidium) 3. Sporangiospores: temperature > 68˚F is indirect germination with 8 motile spore produces * back check first quizlet* 4. Arthrospores: 5. Chlamydospores (arthospores vs chlamydospores; wont need to know the difference between the two but will need to know that sometimes one is created over the other and know those scenerios)

what percent of fungal species actually create plant diseases

2% (most plants are resistant to most pathogens)

The Downy mildews: Downy Mildew of Grape

Best Known downy mildew: New encounter disease - Pathogen: Plasmopara viticola. - Host: Vitis vinifera (European grape) -less severe on the American grape species. 1. Approximately in 1875, pathogen was introduced to Europe from U.S.A. • Danger of introduced pathogens: pathogens are frequently most severe on plants with which they have not co-evolved. 2. Almost destroyed the French wine industry. In the absence of control measures it can easily destroy 50 to 75% of the crop. 3. Led to the discovery of the first fungicide: Bordeaux mixture. Disease progress: 1. Primary inoculum: a. Overwintering Oospore germinates to form a germ tube, which immediately forms a sporangium that is dispersed by wind or water to the host. b. Can overwinter as mycelium in dormant twigs. In spring the fungus forms a sporangium and releases sporangia. 2. Mycelium grows between cells and inserts haustoria into cells for feeding. 3. ASEXUAL CYCLE (polycyclic pathogen; 5 to 18 day cycle) a. Sporangia is formed on sporangiophores. b. Dissemination: Sporangia are blown by the wind, or carried in water to a new plant surface. > Germination requires free water. 2. > Penetration is through stomates. 4. SEXUAL CYCLE: - Meiosis occurs in specialized structures, typical of Oomycetes. • Oogonia ("female") • Antheridia ("male") - Antheridium fertilizes the oogonium, plasmogamy and karyogamy yield the diploid oospore. Control: 1. Host resistance: - Several American varieties have high levels of resistance, but not the European varieties. However, even resistant varieties require chemical protection. • to develop variates that are resistant to the pathogen, can be effective 2. Protective fungicides can be quite effective. - BORDEAUX MIXTURE: 1878, Millardet (French botany professor). Grapes were sprayed with a mixture of copper sulfate and lime. This controlled the disease. • Note: is a copper sulfate mixture which is toxic to both the pathogen and the host cell, to reduce the toxicity to the plant cell but not the fungus cell you add lime. - How does it work? • CuSO4: copper sulfate is toxic to fungus and plant cells too. Lime reduces phytotoxicity. Bordeaux mixture is still the most widely used fungicide in the world (note: #1 chemical mixture to prevent fungus and bacteria pathogens). • Computerized disease prediction systems use weather data to predict infection periods, and time of fungicide applications. 3. Systemic fungicides and soil sprays have also been shown to be effective.

Fungal Vascular Wilts caused by Ascomycetes

Casual Agents 1. Fusarium - Fusarium Oxysporum - Very host specific* - F. oxysporum is the most common, but other fusaria can cause wilts. - Disease is favored by warm soil conditions. - Less of a problem in cooler climates, with the exception of greenhouses. - Hosts: annual vegetables and flowers, herbaceous perennial ornamentals, etc. • Particularly problematic on potato and banana. - Pathogenic specialization (forma speciale: f. sp.): • F. oxysporum f.sp. conglutinans (cabbage) • F. oxysporum f.sp. pisi (peas) • F. oxysporum f.sp. lycopersici (tomato) - These are monocyclic pathogens: produces only once a year so it doesn't reinfect the same plant over and over again 2. Verticillium - More prominent in cooler climates, opposite of Fusarium. - Not host specific. 200 species of host plants. • Annual vegetables, flowers, crop plants, weeds, etc. • Major problem in cotton and in potato, egg plant and tomato. - Conidia move through the plant and germinate. - microsclerotia: compact masses of mycelial mat (can survive up to 15 years). - Fungus can overwinter in the soil as microsclerotia (resistant structure) or in host tissue as mycelium if the host is a perennial. 3. Septoria - Conidia borne in a pycnidia = flask shaped structures. - Disease: Worldwide, cause leaf spots and blights of cereals and grasses. - Disease cycle: • Septoria overwinters as mycelium and as conidia within pycnidia on and in infected seed and on diseased plants left in the field. • Seed borne septoria causes damping-off disease. - Control: • disease free seed • deep plowing of plant material • resistant varieties • fungicides 4. Colletotrichum - Disease: causal agent of Anthracnoses: diseases of foliage, stems, or fruits. • Anthracnose stalk rot: most important corn disease - Spotting, yellowing, and premature leaflet drop caused by walnut anthracnose. Fungal Vascular wilts caused by Deuteromycetes - Fusarium and Verticillium: 1. Both are soil inhabitants and infect through roots. • Wounding promotes infection. Infections are often more severe in association with nematodes, which wound the root and provide a point for entry. > Note: if there is a wound on the root they will infect and then move up to the vasculature system 2. They are effective saprophytes and once established in the soil become permanent inhabitants. - almost impossible to control disease through crop rotation

Phylum Basidiomycota

Characteristics - Basidiomycetes: sexual spores (basidiospores) produced on the outside of the zygote called a basidium (clublike), that is derived from a teliospore. a. dikaryotic vegetative hyphae. b. septate hyphae. c. chitin in cell wall. basidiospores d. Sexual cycle: haploid spores produce a limited haploid mycelium. Two haploid hyphae fuse (plasmogamy) to yield the dikaryotic vegetative state. Nuclei fuse (karyogamy) just prior to meiosis, and the haploid spore is produced Rusts: Order Uredinales 1. Hosts: wide range of plants and crop species. 2. Obligate parasites. 3. Not usually systemic pathogens, mostly local lesions. 4. Very host specific. - Puccinia graminis: forma speciale (f. sp.) a. P. graminis f.sp. tritici: race specific to wheat . b. P. graminis f.sp. hordei infects barley 5. Complicated life cycles: A. One or two hosts required for completion of their life cycle. - heteroecious rusts: two hosts in life cycle. - autoecious rusts: one host in life cycle. B. Multiple spore stages. - macrocyclic rust: Typically produces all 5 spore types (teliospores, basidiospores, spermatia*, aecia, uredospores*). *may be absent. - microcyclic rusts: Produce only two spore stages (teliospores and basidiospores). (Need to know about rusts is how many hosts does its lifecycle have?) Smuts (bunts): - Order Ustilaginales. (1200 species of smut fungi). - Important grain pathogens, particularly prior to the availability of systemic fungicides and advanced breeding programs. - Direct yield reduction, as the teliospores of the fungus replace the kernel. - Most smut fungi attack the ovaries of grains and grasses and develop in kernels which destroys the crop. - Hosts: grains and grasses. Usually considered pathogens of cereals, but can affect sugarcane, onions, and some ornamentals. 1. Corn Smut - Ustilago maydis. 2. Loose Smut - Ustilago spp. (ex. tritici). 3. Covered Smut (Also called Bunt or Stinking Smut) Tilletia spp. Root and Stem rots: Wood rotting Fungi:

Canker diseases of trees caused by Ascomycetes: Oak Wilt

Pathogen: Ceratocystis fagacearum (Ascomycete that is heterothalic: needs two mating types) • not a cancer pathogen but a vascular wilt Hosts: Oak Wilt is most common on red oaks but it will also cause serious damage on certain other oaks, including post oak. Transmission 1. Root grafts - The pathogen primarily moves from tree to tree through root grafts. - Adjacent oak trees within 50 feet often have a common root system because roots are grafted or "fused" to one another. - If one tree becomes infected, it is relatively easy for the fungus to move from tree to tree through a common root system. - This root movement is why oak wilt usually occurs in pockets of trees. 2. Animal Vectors - The oak wilt fungus may also be moved from tree to tree by insects and possibly by small mammals or birds. • Nitidulid beetle: attracted to sweet things (like the smell produced from wilts or anything that produces fungal area) - This method is not very efficient (unlike insect transmission of the Dutch elm disease fungus among elms). Therefore, it is important to concentrate on root-to-root spread of the oak. Fungal mats: - Commonly produced between April and late June on red oaks that wilted during the previous summer. - Fungal mats of the oak wilt fungus are produced underneath the bark. - These mats smell fruity and attract Nitidulid beetles (vector) Control: - Dig trenches (ecologically disruptive - burn and cut down red oak - something else unsure back

The downy mildews: Downy mildew of Impatiens

Pathogen: Plasmopara obducens

Diseases caused by fungi from the Kingdom Fungi

Phylum Chytridiomycota: Chytridiomycetes are water and soil-inhabiting fungi. • obligate parasites/biotrophs. (why they are so good at spreading viruses) • zoospores with a single flagella. - Olpidium = root diseases & vectors for viruses • Examples: > Olpidium brassicae: The vector of lettuce big-vein virus. º Has a resting spore stage that is thick-walled, is virtually impossible to eradicate once established in field soils and can survive for an excess of 20 years in the absence of suitable hosts. - Physoderma = black wart of potato • The potato wart disease is a serious potato disease • The spores released by the tumors can remain alive for many years (up to 30 years) in the soil, in encysted form. • The attacks are particularly severe in a cold and damp climate - Physoderma alfalfae = crown wart of alfalfa • galls form on the young crown buds of alfalfa - Physoderma = brown spot of corn Phylum Zygomycota - Rhizopus and Mucor-soft rot of fruits and vegetables Phylum Ascomycetes: - Sphaerotheca pannosa = powdery mildew of rose - Venturia inaequalis = Apple scab - Monilinia fructicola = Brown rot of stone fruits - Ceratocystis ulmi = Dutch Elm disease (DED) • in depth below Canker diseases of trees caused by Ascomycetes - Cryphonectria parasitica = Chestnut blight • in depth below - Ceratocystis fagacearum = Oak wilt • in depth below Fungal and Vascular wilts caused by Ascomycetes 1. Fusarium 2. Verticillium 3. Septoria 4. Colletotrichum Phylum Basidiomycota (Club and mushroom fungi) 1. Rusts 2. Smuts (Bunts) 3. Root and Stem Rots 4. Wood rotting fungi

Kingdom Chromista

Phylum: Oomycota "Oomycetes". - "Name a major characteristic of the kingdom Chromista? Diploid hyphae, coenocytic etc... below" - Cell wall is composed of glucan and a small amount of cellulose. • diploid hyphae (2n). • coenocytic (no cross wall). • zoospores (asexual) are produced in zoosporangium. • oospore (sexual) are in oogonium. - Examples: • Pythium spp.: causes "damping-off" of seedlings, seed decay, root rot, etc. • Phytophthora infestans (late blight of potato, tomato). • Downy mildews: obligate parasites. - can not be cultured in Koch's postulates º Caused by several different genera. > downy mildew of grapes. > blue mold (downy mildew) of tobacco. > downy mildew of lettuce.

Basidiomycetes: Cereal rusts

The most important rust economically - Hosts: All grasses, including cultivated and wild. - Each year about $500 billion dollars is lost to cereal rusts. - Wheat, barley and oats have origins in Asia Minor. Their respective rusts probably have their origin there as well. - Archaeological digs in Israel have uncovered rust spores on grain from at least 3,000 years ago. - An Example: Stem rust of wheat Stem Rust of Wheat Most important rust of cereal crops, most devastating rust that we have to deal with. - Host: Wheat (Triticum aestivum). Most important crop of both ancient and modern times. - Modern days: More than 1 million metric tons of wheat are lost in N. America to stem rust each year. - Pathogen: Puccinia graminis* (most important pathogen for wheat) 1. Obligate parasite. 2. Very host specific. 3. Heteroecious, macrocyclic rust. • Two hosts: Wheat and Common Barberry. • 5 spore stages. 4. Distribution: worldwide. - Symptoms: Symptoms are produced on almost all aerial parts of the wheat plant but are most common on stem, leaf sheath and upper and lower leaf surfaces. - Penetration: penetration through stomates (Cereal Rusts, in general). 1. Thigmotropic mechanisms. a. They can locate stomate opening on physical, non-biological, casts of the leaf surface. b. If the epidermis is removed, the physical cues are removed, and the germ tube wanders around the leaf surface without penetrating. c. Recent studies suggest that they use the distance between epidermal cells, and the height of the guard cell lip as physical cues. 2. Chemotropic mechanisms. - P. graminis infection structures can be induced by volatile compounds from the host. - Infection: They invade plants intercellularly, and insert haustoria to obtain nutrients. - Role of the barberry as alternate host: - The first recorded legislative act concerning a plant disease was passed in France to eradicate barberry plants. - Farmers noticed that rust was often worst near barberry bushes, but the effect was not understood. - Control: 1. Eradication: eliminate barberry. 2. Fungicides: wheat has a low cash value/acre, and fungicides are often not cost effective. 3. Host Resistance in Wheat (Main approach to control) 4. General (horizontal) resistance (non-specific). This is a primary goal, in particular due to the unstable nature of vertical resistance. 5. Plant multiline wheat cultivars -8 to 10 lines that differ in specific resistance genes. Cedar- Apple Rust