ppem 405 exam 2

Aeciospores

(n+n) on underside of barberry leaf. Infect only wheat plants wind blown to wheat host plants and infect leaves by penetrating stomates.

Spermacia

(n-) and (n+) Receptive Hyphae on upper barberry leaf surface

PATHOGEN: Puccinia graminis f. sp. tritici

HOSTS: Wheat and barley, common barberry (and some additional Berberis, Mahoberberis, and Mahonia spp.)

Armillaria root rot Symptoms: External

Above-ground symptoms on individual trees are variable and not specific to this disease or even to root diseases in general. It is not uncommon for the disease to be very advanced but showing no obvious symptoms. Symptoms include: • reduced terminal growth (most detectable in conifers) • dieback of twigs and branches (most apparent in hardwoods) • chlorosis of needles • stunted leaves • crown thinning • premature fall coloration (hardwoods) • basal resinosis (conifers) • heavy production ('stress crop') of cones or fruits

Structures of mushrooms

All vegetative hyphae and visible structures are n+n annulus gills stipe volva

Leaf curl disease caused by Taphrina

Species in this genus cause: • Leaf curl on peach and nectarine • Plum pocket on plums • Leaf curl and witches' broom on cherries • Leaf blister on oak

FHB sexual reproduction

Brightly colored perithecia that frequently form in stromata (somatic structures on which fruiting bodies develop). The perithecia of G. zeae are a dark blue in color at maturity. Ascospores (sexual spores) form within sacs called asci, and are forcibly discharged from the perithecium through a single small opening known as an ostiole. The ascospores are hyaline to light brown in color, and slightly curved with rounded ends

Ascomycota - asexual reproduction

Conidiophores -aerial vegetative hyphae producing conidia Conidia -1n haploid spores produced by mitotic cell division Pycnidia, synnema, sporodochia and acervula are the names of the asexual structures seen in class

Disease forecasting

FHB is well suited for disease forecasting because of its narrow time periods of pathogen sporulation, spore dispersal, and host infection that contribute to epidemic development. Disease forecasting models for FHB have been developed and are widely used. These models incorporate factors such as temperature, humidity, rainfall, inoculum production, and plant development as predictors for the severity of FHB.

inside the fungal cell

Fungal nuclei are usually small (< 2 µm diameter), and can stretch to move through septal pores and into developing spores. Fungi have between 6 and 21 chromosomes coding for 6,000 to nearly 18,000 genes. Genome sizes range from 8. 5 Mb to just over 400 Mb in filamentous fungi, making fungal genomes among the smallest of eukaryotic organisms— Many fungi (Ascomycota) have a life cycle that is predominantly haploid, while others (Basidiomycota) have a long dikaryotic phase.

WOOD ROT Disease development

Fungi enter trees as basiospores or mycelium through wounds • Fungi spread up and down from the infected point • Decay is helped by other bacteria and fungi that soften wood on wounded surfaces • Decay becomes fast once wood is colonized and compromised • Decay can take from few to hundred years

meiospore

ascospores in an ascus basidiospores in a basidium

A case of floral mimicry

It tricks pollinators to land on infected leaves by changing the color of infected tissues (seen under UV) and by changing the volatile composition of leaves (they smell sweet and they produce sugars!) • Pollinators are now coated with sticky fungal spores and they transport them on healthy flowers • Fungal spores germinate together with pollen and reach the flower embryo • Fungal spores germinate together with the formation of the fruit

FHB asexual reproduction

The anamorph (asexual state) is Fusarium graminearum. Macroconidia (asexual spores) are derived from conidium-producing cells called phialides. The phialides are clustered together in cushion-shaped masses known as sporodochia. The macroconidia are hyaline, canoe-shaped spores usually with five or more septa.

formation of ascospores and conidia

Mycelia cells in plants contain 2 nuclei. When they are close to the plant surface, they can germinate in an ascus that can produce 8 uninucleate ascospores • Ascospores can be dispersed and bud, or they can bud inside the asci forming conidia • Conidia can bud in more conidia or can germinate in mycelium. • Fungus overwinters as ascospores or thick wall conidia on the tree and inside bud scales. • In spring rain splashes the spores on young tissues, where they can penetrate via germination or via stomata. • Mycelial growth between cells causes cell distortion • Ascospores are dispersed by wind and blow on new tissues after bud opens • Tissues are not susceptible when older • Low temperature and humidity during young tissue development favor diseases

septa

Presence or absence of septa or cross walls are characteristic. • Septa are perforated and allow passage of organelles and cytoplasm

Disease Management of Fusarium head blight

Resistant cultivars. To date, sources of resistance conferring complete resistance to FHB have not been identified in wheat. Crop sequence and tillage have been shown to affect the incidence of FHB. Decreases in tillage are thought to have contributed to regional scab epidemics by increasing levels of inoculum available for infection. In regions where there is a significant source of airborne inoculum, local management of the disease (on a single farm) may not be effective. Chemical controls, such as fungicides, provide partial control of FHB and associated mycotoxin contamination. Foliar fungicides are applied around the period of wheat flowering. Fungicides for seed treatment also reduce the risk of Fusarium seedling blight. Biocontrol agents could play an important role in organic cereal production. Integrated management of FHB may one day be achieved by the combined application of biocontrol agents and fungicides to flowering wheat and barley varieties with partial resistance.

Sexual reproduction

Sack-like Ascus (Asci) Ascospores produced by meiosis 8 ascospores per ascus Ascospores are each 1n

fusarium

Teleomorph, when present: Gibberella. • Fusarium is a large genus of filamentous fungi, widely distributed in soil and associated with plants. • Can produce growth regulators and mycotoxins. • Many Fusarium species produce mycotoxins-- fungal chemicals that are harmful to animals. These chemicals may operate in nature to disable plant defense mechanisms or to defend the fungus against other microorganisms. • Important Fusarium not covered in class: Fusarium wilt of banana, or Panama disease, caused by Fusarium oxysporum f. sp. cubense.

Armillaria root rot Symptoms: internal

The disease may develop as butt rot in some situations and as cambial killing in others. The difference may be related to stress and host differences. If the host is resistant, a major wound may be required for infection, and the fungus would be restricted to inner, inactive wood (butt rot). If the host becomes stressed, the fungus is then able to attack cambial regions, even of unwounded trees. • Clear mortality centers, from a few trees to several hectares, may be seen in some cases and not in others. • The decay is a spongy, often wet, white rot. Zone lines can usually be found in the decayed wood. In hardwoods the decay often has a gelatin in it. This pathogen is very generous in providing oodles of signs to allow diagnosis. They all require some experience to identify to the genus Armillaria with certainty. They are: • Mycelial fans (like soft, white, peelable paint) can be seen under the bark of tree portions that are colonized while the tree is alive or shortly thereafter • Rhizomorphs • Mushrooms

Sclerotium Disease development

The fungus overwinters as sclerotia • It spreads though infested soil, water, plant material • It can be spread by tools and tractors • Sometime seeds and sclerotia are mixed together • The fungus attacks the host, then it produces pectinolytic and cellulolytic enzymes that destroy host tissues before fungus penetration • Once inside the host the fungus produces mycelium and sclerotia and invades the upper crown and roots

what do fungi do

some decomposers, parasites, pathogens others beneficial through symbiosis with plants, animals and algae lignin is a complex polymer fungi can break down

Rhizoctonia solani - Disease development

The pathogens overwinters as sclerotia in the soil or as mycelium in infested plant debris or material such as tubers • It can be carried in some seeds • When present in the soil it remains there and it is hard to eradicate • Dry or waterlogged soils disfavor the disease, while moderate wetness favors it • The pathogen spreads with rain, irrigation or flood water, by contaminated soil and plant material

Rhizoctonia species are strong saprophytes.

They are able to survive for extended periods of time in the absence of living host plants by feeding on decaying organic matter. When conditions are not favorable for growth, these fungi persist as mycelium or as sclerotia in the thatch and soil.

species of fungi

at least 99,000- new species 1200/ year estimate 1.5 million species many people extinct before they are discovered do to habitat and host loss 2% of tropical forests destroyed/ year

Fusarium head blight (FHB)

caused by Fusarium graminearum (anamorph) Gibberella zeae (teleomorph) • Is one of the most devastating plant diseases in the world. • The United States Department of Agriculture (USDA) ranks FHB as the worst plant disease to hit the US since the rust epidemics in the 1950s. • Since 1990, wheat and barley farmers in the United States have lost over $3 billion dollars due to FHB epidemics. Canada has also experienced severe losses since 1990.

cell wall composition

cell wall in the Kingdom Fungi is composed of chitin and glucans (in Ascomycota, Basidiomycota and Chytridiomycota) as well as chitosan and other components (in Zygomycota)

characteristics of fungi

eukaryotes digest food externally and absorb nutrients through cell walls by secreting enzymes heterotrophs (obtain carbon and energy from other organisms) some biotrophs (nutrients from living host) some saprophytes (nutrients from dead hosts) some necrotrophs (in fect living and kill host cells)

role and association of fungi

fungi can grow on and in invertebrate and vertebrate animals can attack and control populations of insects and nematodes entomopathogens- insect attacking fungi human fungal infections- mycoses

history of fungi

may have arisen over 1 billion years ago bacteria 3.5 millions years old fossil record incomplete, minimum time estimate for when . different groups of fungi evolved

Rhizoctonia species are necrotrophic pathogens

meaning that they kill host cells before colonizing them. This is accomplished through the secretion of enzymes and toxins in advance of fungal growth.

fungi and plants

most plant diseases are caused by fungi but less than 10% of fungi colonize living plants most fungi are decomposers endophytes- beneficial symbionts and cryptic plant colonizers

Distinguishing Characteristics of Ascomycota

ploidy 1n chitin cell wall septa

Urediospores

s ( n+n) erupt from upper leaf surface. Repeating stage.

fungi as plant pathogens

thousand of plant pathogenic fungi= 70% of all know plant diseases plant parasitic fungi obtain nutrients from living plant host, but the plant host doesn't necessarily exhibit any symptoms plant pathogenic fungi are parasites and cause disease characterized by symptoms

Ug99

• A new race of the wheat stem rust fungus highly virulent to wheat varieties with Sr31 resistance was found in Uganda in 1999. • Ug99 spread to Kenya and Ethiopia and was found in South Africa and in Yemen, from which it has spread to the north and east as far as Iran. • Scientists are worried that Ug99 will soon invade one of the world's richest wheat producing areas in India. • The Ug99 lineage of the stem rust fungus has expanded its virulence through mutations that allow it to overcome the resistance of at least two other vertical resistance genes that wheat breeders have relied on for protection from stem rust in North America and many other parts of the world. • The fungus has been seen in many countries in East Africa, West Asia and parts of Europe.

control of peach leaf curl

• Annual management is recommended. • To successfully control the disease, treatment timing is crucial. • This disease is usually kept under control with a dormant fungicide application, but in wet years more than one spray application may be needed (in late winter or early spring).

Armillaria root rot Significance of the disease

• Armillaria root disease is often one of the most important diseases of trees in temperate regions of the world. • Substantial disease losses occur in temperate portions of North America, Europe, Asia, Japan, southern Africa, Australia, and New Zealand and certainly elsewhere. • The disease also occurs in some tropical areas, including tropical portions of Africa, South America, and Sri Lanka, but in many cases it is less serious than in temperate areas, or occurs primarily at high elevations.

Basidiomycetes

• Basidiomycetes produce their sexual spores (basidiospores) on club-shaped basidia • Typically Basidiomycetes are fleshy fungi or common mushrooms, but they can also be rusts and smuts • They can cause devastating diseases

Sclerotium and Rhizoctonia

• Can affect roots, stems, tubers • Both produce sclerotia, important survival and dispersal structures

Smut Diseases of Plants

• Common Genera: • Ustilago, Tilletia, Urocystis • Over 1200 species • Attack ovaries of grains and grasses. • Replace kernels with sooty, smutty spores masses. • "Smut" means dirt

Rhizoctonia

• Composed by many different fungi (called Rhizoctonia complex): each species is a 'collective species' • Can attack vegetables, flowers, grasses and some trees • Cosmopolitan • Can cause: Damping off of seedlings, stem rots, root rots, stem cankers, spots on lower leaves, rotting of storage organs • These fungi do not produce asexual spores, but grow by producing hyphae • In recent years, the sexual stages, or teleomorphs, of many Rhizoctonia species have been characterized. However, these sexual stages are rarely seen in nature • Anastomosis is the primary means of genetic recombination in Rhizoctonia, therefore, isolates within an anastomosis group are closely related to one another. As a result, isolates within anastomosis groups (AGs) tend to have similar host ranges.

Disease control

• Control is very difficult • Deep plowing to bury sclerotia can be used • Crop rotation • Use of calcium compounds, use of ammonium type fertilizers or fungicide achieve only partial disease control • Biocontrol agents such as parasitizing or antagonistic bacteria and fungi could become prevalent

Large Patch- Control

• Cultural Management: Control of moisture levels in the thatch and soil. The disease is most severe in areas that have poor soil drainage, little air movement, or excessive shade. Installation of drainage tile, soil cultivation to reduce compaction and thatch accumulation, and/or modification of the soil profile to increase porosity will limit large patch severity and improve overall turf quality. Where air movement and sunlight penetration are low, pruning or removal of surrounding trees and shrubs is recommended. Irrigation should be applied as necessary to meet the water requirements of the turf. • Mowing height may also influence the development of large patch. Reduced mowing heights result in a more dense turf stand, which may create a more favorable environment for large patch development by reducing air movement and increasing humidity in the lower turf canopy. • Chemical Control: Several fungicides are available for control of large patch. In turf stands with a history of large patch development, preventative fungicide applications provide excellent control when timed properly. The first application should be made in the fall when conditions become conducive for large patch development, i.e. when the thatch temperature drops below 21°C (69.8°F) for several consecutive days. Subsequent applications should be made as specified on the fungicide label. Because the majority of disease development occurs in the fall, fungicide applications at this time are most important. However, when disease pressure is severe, spring applications may also be required to achieve adequate control. • Genetic Resistance: Little variation in large patch susceptibility is observed among the warm-season grasses

Brown Patch-Control

• Cultural Management: Moisture and temperature are the most common factors limiting brown patch development Rhizoctonia solani requires a minimum of 10 consecutive hours of leaf wetness or relative humidity ≥95% in order to initiate disease. Practices that reduce the amount of time that the turf canopy is wet or humid will therefore reduce the severity of brown patch. • Irrigation water should be applied infrequently, but in sufficient amounts to meet the water requirements of the turf. Irrigation should be timed so that the duration of leaf wetness is minimized. Early morning irrigation removes large droplets of dew and guttation water, which evaporate slowly, from the foliage and encourages rapid drying of the turf. Avoid irrigation for several hours prior to sunset. When syringing turf during the day to reduce heat stress, ensure that the turf canopy dries completely between syringe cycles • Early morning mowing also reduces leaf wetness duration by removal of large dew droplets and guttation water from the leaves. Alternatively, dew can be removed by dragging a pole, hose, rope, chain, or other object across the turf surface. • In areas where sunlight penetration and air movement are low, pruning or removal of surrounding trees and shrubs will help to reduce brown patch development by facilitating water evaporation and improving overall turf vigor. For high maintenance sites, such as golf greens, installation of high-powered fans increases air movement, speeds morning drying of the turf and reduces the incidence of several diseases. • Installation of drainage tile, core cultivation to reduce soil compaction and thatch accumulation • Excessive levels of nitrogen fertilizer enhance brown patch activity. Nitrogen fertilizer should be applied in small quantities during the summer months to reduce brown patch severity. • Chemical Control: In warm, humid climates, where brown patch pressure is consistent throughout the summer months, preventative, calendar-based applications are recommended for brown patch control. In more temperate climates, where disease development occurs intermittently, applications may be made on a curative basis or according to a disease forecasting system. • Genetic Resistance: Turfgrass species vary significantly in their susceptibility to Rhizoctonia species.

smut details

• Dark-colored teliospores form in bunted kernels and are the overwintering structures. • They are released from infected plants and land on healthy seeds or on the soil surface. Karyogamy and meiosis occur in the teliospore. • When environmental conditions are favorable, each teliospore germinates by producing a basidium. Shortly after the basidium is formed, long thread-like, lightcolored, haploid basidiospores are produced, four or more per basidium • Genetically compatible basidiospores anastomose (fuse) very quickly to form an H-shaped structure which allows the haploid nuclei in the two sporidia to come together as a dikaryon. The two nuclei do not fuse together, but function as a pair. An infectious hypha develops from the H-structure. This dikaryotic hypha penetrates into the tissue of a germinating seedling and establishes itself just behind the growing point or apical meristem of the wheat plant. • Infection of wheat by the common bunt pathogen represents a race in which the fungus attempts to reach and establish itself in the developing apical meristem of each tiller before internode extension rapidly moves the apex upwards beyond the reach of the fungus. • If environmental conditions favor the pathogen, infection and a consequential bunting of the majority of spikes of a susceptible cultivar will occur; • if conditions are not optimal or if plant defense responses impede or stop pathogen ingress, infection will fail resulting in few or no spikes being infected. • Just when the wheat head is formed, the hyphae of the smut fungus invade the newly developed seed and begin proliferating rapidly. The hyphae replace the cells of the seed, so that finally only the seed coat remains. Individual cells of the smut fungus then "round up" to form the black, smelly teliospores. The two nuclei eventually fuse to form a diploid nucleus in the teliospore. • Cool temperatures (5-15°C/41-59°F) favor the germination of the teliospores. Usually the soil moisture, which favors seed germination, also favors spore germination. • For winter wheat which is planted in the fall, infection is favored when the seed is planted later when soil temperatures are cooler. • Planting winter wheat early late when the soil temperature is above 20°C (68°F) results in very low infection. • Early seeding of spring wheat when soil temperatures are cool favors infection.

Brown Patch Symptoms and Signs

• Disease of cool-season grasses, including bentgrasses, bluegrasses, fescues, and ryegrasses. • Commonly occurs during periods of warm and humid weather • Brown or tan patches of diseased turf ranging in diameter from 5 cm (2 in.) up to 1 m (3 ft) or more in diameter • When close-cut turf (<2.5 cm or 1 in.) is wet, brown patches are often surrounded by a dark brown or gray ring called a "smoke ring". The smoke ring is evidence of active fungal growth on the turf foliage and is an initial sign of brown patch development • Brown patch typically does not result in damage to all tillers within a developing patch, therefore, the turf may recover when disease pressure is reduced by change in weather conditions or implementation of control practices • Symptoms observed on individual plants vary according to the height of mowing. On turf maintained above 2.5 cm (1 in.), irregular silvergray or tan lesions with a thin, dark brown border are observed on the leaves On close-cut turf (<2.5 cm or 1 in.), no distinct lesions are readily observed, but the symptoms appear as general leaf necrosis.

Large Patch Symptoms and Signs

• Disease of warm-season grasses, including bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass. • Occurs during the spring and fall, when warm-season turfgrasses are entering or exiting their period of winter dormancy. • Circular patches of diseased turf are observed, ranging in diameter from less than 1 m (3.3 ft) up to 8 m (26.4 ft) • Leaves of recently infected turf, located at the periphery of the patch, may appear orange in color • Some patches may be perennial, recurring in the same location and expanding in diameter year after year. • In contrast to brown patch, R. solani infection of warm-season grasses occurs on the leaf sheaths, where water-soaked, reddish-brown or black lesions are observed. Foliar dieback from the leaf tip toward the base occurs as a direct result of these leaf sheath infections.

Environmental factors that favor FHB

• FHB infection is favored by extended periods of high moisture or relative humidity (>90%) and moderately warm temperatures (between 15 to 30°C/ 59 to 86°F). • These conditions present before, during, and after flowering favor inoculum production, floret infection, and colonization of developing grains.

Rusts are very specific

• Formae speciales (f.sp.) - "special forms" • Puccinia graminis f.sp. tritici - wheat • Puccinia graminis f.sp. secalis - barley • Rust fungi are obligate parasites. In nature, they require living host tissue for growth and reproduction; they cannot exist as saprophytes. In the absence of living host tissue, they survive as spores. In most rust fungi, only the teliospores are adapted to survive apart from a living host plant for more than a few months under field conditions. • Pathogen recognizes host morphology - only then will it penetrate and infect. • Guard cells of stomata • Leaf topography

reproduction

• Fungi frequently reproduce by the formation of spores. • A spore is a survival or dispersal unit, consisting of one or a few cells, that is capable of germinating to produce a new hypha. • Unlike plant seeds, fungal spores lack an embryo, but contain food reserves needed for germination. • Many fungi produce more than one type of spore as part of their life cycles. • Fungal spores may be formed via an asexual process involving only mitosis (mitospores), or via a sexual process involving meiosis (meiospores). Many fungi are able to reproduce by both sexual and asexual processes. • Sexual and asexual reproduction may require different sets of conditions (e. g., nutrients, temperature, light, moisture). • In some fungi, two sexually compatible strains must conjugate (mate) in order for sexual reproduction to occur. • The terms 'anamorph' and 'teleomorph' are used to convey the asexual and sexual reproduction morphological types, respectively, in a particular fungus

Mycorrhizae

• Fungi that are associated with feeder roots • Every plant and grass is associated with them! • Usually the symbiosis between these fungi and their hosts is beneficial • In absence of the host mycorrhizae remain in the soil as dormant spores or resistant hyphae • Absence of mycorrhizae in fumigated soil reduces plant growth • The length of the association is regulated by nitrogen level in the plant

Brown and white rots

• Fungi that cause brown rots degrade cellulose and hemicellulose but can not degrade lignin • Fungi that cause white rots degrade mainly lignin, and eventually cellulose and hemicellulose List of important basidiomycetes: 1. Heterobasidion 2. Phellinus 3. Ganoderma 4. Inonotus 5. Armillaria

growth of fungi

• Hyphae grow from a germinating spore or other propagule • Hyphae elongate almost exclusively at the tips, growing outwards from the point of establishment. • As a result, hyphae are relatively uniform in diameter, and mycelium that grows in an unimpeded manner forms a circular colony

Mycorrhizae benefits

• Increase the absorbing capacity of feeder roots • Endomycorrhizae increase resistance of roots to pathogenic fungi • Alleviate water stress • Solubilize insoluble minerals • Accumulate nutrients such as phosphorus • Increase life span of roots

Effects of Smut

• Infections not limited to flowers... • May also infect seeds or seedlings (grow internally) • Also infect stems and leaves, replaces cells with spores • Seldom kills host • Yield reductions: • Quantity: destroys kernels • Quality: smell and taste

Armillaria root rot (Armillaria mellea and other species); white rot of wood; A Glowin-the-Dark Fungus

• It affects many woody angiosperms (hardwoods) and gymnosperms (conifers) in native forests, planted forests, orchards, vineyards, and in amenity plantings in urban areas. Some nonwoody plants (such as strawberry and potato) are also hosts • Armillaria mellea is the most common fungus in forest soil • It is prevalent in recently deforested soils • Armillaria species can be a problem in forests if the trees are stressed by drought and defoliation

Sclerotium

• Its diseases occur in warm climates • Can cause seedling damping-off, stem canker, crown blight, rots of fruits, bulbs and tubers • It is a big problem during fruit and vegetable storage and shipment • It can affect legumes, flowers, vegetables, cereals, forage grasses and weeds. • Infected material is usually covered by white mycelium • The fungus produces numerous sclerotia

Taphrina deformans

• Main losses are caused on peach, nectarine, plum. • The disease occurs all over the world • Defoliation of trees causes reduction in fruit size • Can cause 50% losses in plum production

brown rot control

• Make a chemical treatment at 20 to 40% bloom and again at 80 to 100% bloom on susceptible varieties or if heavy rainfall and other conditions are occurring that result in high susceptibility to infection. • Remove twigs with cankers • Apply fungicides well before harvest and reapply many times, if conditions are conducible to disease development • Control insects for wounds on fruit • Removal of fruit remaining on trees soon after harvest before they become mummies helps prevent reinfection of blossoms the following bloom. • Handle fruits with care, discard diseased fruits, dip in fungicides and store at cool temperature

Reproduction of Fungi

• Most fungi reproduce by spores and have a body (thallus), called mycelium, composed of branching microscopic tubular cells called hyphae • Hyphae have contributed to the successful exploitation of diverse ecological niches by fungi • Hyphae grow through substrates or food sources, secreting enzymes that break down complex substrates into simple compounds that can be absorbed back through the cell wall

Armillaria root rot Disease cycle

• Mycelium can grow through direct root contacts and grafts with uninfected trees • Rhizomorphs can grow through soil to contact uninfected trees • Mushrooms produce basidiospores, which are winddispersed to wreak death and destruction in new places, under the correct environmental circumstances *very rare event

wood rot disease control

• New growth in trees can halt the spread of the fungus • Control in forest is impossible, but avoiding wounds, harvesting older trees in tree stands and avoiding the import of the pathogens in new areas can help minimizing the damage. • Antagonistic fungi can be painted on pruning wounds and can be added to the oil that lubricates the chain of saws. • Harvested lumber wood can be dried and treated with chemicals to help preservation and stop the fungi

Puccinia graminis

• Obligate biotroph - no saprophytic stage • Heteroecious - 2 hosts required for lifecycle: • Grass species (monocot) • Barberry (dicot) • Polycyclic pathogen • Aerial urediospores spread 100s of miles • Plants do not usually show obvious disease symptoms until 7 to 15 days after infection when the oval pustules (uredinia) of powdery, brick-red urediniospores break through the epidermis. The pustules may be abundant and produced on both leaf surfaces and stems of grass hosts.

Brown rot of stone fruit by Monilinia

• Occurs in seasons when rains occurs during blooming and during fruit ripening • Losses occur in orchards but also during shipment and marketing • It can create huge losses in flowers numbers and in fruit rotting

Stinking smut (common bunt) of wheat

• PATHOGEN: Tilletia tritici, Tilletia laevis • HOSTS: Wheat, bread and durum • The earliest evidence of infection occurs shortly after ovaries would normally be pollinated. Infected ovaries appear greasy with a dark green cast. When squeezed, such ovaries reveal a mass of black spores that smell like rotting fish. This odor is actually that of trimethylamine, which is produced by the smut fungus. • As the heads and kernels mature, the bunt balls develop into a hardened mass that looks like miniature footballs. The spores inside the mature bunt balls are released when the heads go through the combine harvester to produce the cloud of dust • This dust also smells of rotting fish. Occasionally, both healthy seeds and bunt balls are found in the same head.

Common smut of corn (Syn. boil smut, blister smut)

• PATHOGEN: Ustilago maydis (Syn. Ustilago zeae) • HOSTS: Maize (Zea mays), teosinte (Zea mexicana) • Occurs wherever corn is grown • Sweet corn especially susceptible • Reduces yield by forming galls on aboveground tissue: • Ears, leaves, silks, tassels • Galls full of teliospores • Young galls are edible!

Rusts

• Puccinia - grass and cereal rusts • Phakopsora - Soybean Rust • Gymnosporangium - Cedar-Apple Rust • Hemileia - Coffee Rust • Cronartium - White Pine Blister Rust • Uromyces - carnation and bean rusts • Phregmidium - Orange rust of blackberry • Rusts are among the most important plant pathogens in the world

Control of Wheat Rust

• Resistant varieties. At least 50 distinct genes for race-specific (vertical) resistance to stem rust have been identified in wheat or transferred to wheat by wide crosses to wild relatives of wheat. • Earlier-maturing varieties • Fungicides • Many applications required = $$$ • Scouting and Forecasting • Barberry Eradication, started in 1918 and still partially ongoing today. • What are the advantages and disadvantages of barberry eradication?

Root and Stem Rots

• Sclerotium and Rhizoctonia attack mainly herbaceous plants • Armillaria, Heterobasidion and Phellinus attack mainly trees

dimorphism

• Some fungi can switch between mycelial growth and yeast-like growth, dependent upon the environmental conditions (dimorphism)

yeast

• Some fungi grow as yeasts, singlecelled fungi that reproduce by budding or fission. • yeasts exhibit wall growth over the entire cell surface, often resulting in a nearly spherical cell

Most rusts have up to 5 spore types

• Spore Stage II: Urediospores in uredia (sing.=uredium) • Spore Stage III: Teliospores in telia (sing.=telium) • Spore Stage IV: Basidiospores on basidia (sing.=basidium) • Spore Stage 0: Spermogonia (sing.=spermogonium) (consists of Receptive hyphae and Spermatia [sing.=spermatium]) • Spore Stage I: Aeciospores in aecia (sing.=aecium)

smut control

• Systemic fungicides. To date, no significant problems have occurred with the development of fungicide resistance in the smut fungi. This is probably due to the fact that there is only one cycle of reproduction of the smut fungus each year, rather than multiple cycles as occurs in many of the foliar infecting fungal pathogens where fungicide resistance has been well documented. • Seed treatment is relatively inexpensive, very effective, and environmentally safe since very little of the active ingredient is applied per unit of land. For growers who do not want to use chemical seed treatments, the use of organic seed treatment does offer some control, i.e., use of skim milk powder. • Resistant Cultivars of Wheat Not much effort spent finding resistant cultivars, since seed treatment is so successful. While most planted cultivars are susceptible to stinking smut, some are resistant • Seeding Date Either early fall seeding for winter wheat, or late spring seeding for spring wheat. While this practice can reduce the incidence of smut, it rarely eliminates the disease altogether. Generally, stinking smut is more of a problem in winter wheat than in spring wheat due to the longer period of more favorable temperatures for teliospore germination in the autumn when winter wheat is planted.

smut Life/Disease Cycle

• Teliospores (n+n) • Found in galls • Overwinter in soil/plant debris • Basidiospores (n) • Infect growing tissue • Direct penetration • Germinate, compatible (+ and -) hyphae fuse to form dikaryotic mycelium .

Arbuscular mycorrhizae

• most common and widespread of all mycorrhizae and are found in as many as 85%-90% of the world's plant species • In this association the fungus occurs inside the cells of the plant root as a highly branched shrubby structure called an arbuscule

Ectomycorrhizae

• occur on the roots of about 5% of the world's plants. • the fungus never penetrates the cell walls of the plant and thus the exchange of nutrients must take place not only through the cell membrane but through both plant and fungal cell walls as well.

FHB symptoms and signs

• The first symptoms of Fusarium head blight occur shortly after flowering. Diseased spikelets exhibit premature bleaching as the pathogen grows and spreads within the head. Over time, the premature bleaching of the spikelets may progress throughout the entire head • If the environment is warm and moist, aggregations of light pink/salmon colored spores (sporodochia) may appear on the rachis and glumes of individual spikelets • Later in the season, bluish- black spherical bodies may appear on the surface of affected spikelets. These bodies are sexual structures of the fungus known as perithecia, and can be seen readily in laboratory cultures on carrot agar medium • As symptoms progress, the fungus colonizes the developing grain causing it to shrink and wrinkle inside the head • Often, the infected kernels have a rough, shriveled appearance, ranging in color from pink, soft-gray, to light-brown

Stem rust causes cereal yield losses in several ways:

• The fungus absorbs nutrients from the plant tissues that would be used for grain development in a healthy plant. • As pustules break through the epidermal tissue, it becomes difficult for the plant to control transpiration, so its metabolism becomes less efficient. • Desiccation or infection by other fungi and bacteria also can occur. • Interference with the vascular tissues results in shriveled grains. • Stem rust also can weaken wheat stems, so plants lodge, or fall over, in heavy winds and rain. • Where severe lodging occurs, crops cannot be mechanically harvested.

brown rot details

• The fungus overwinters as mycelium on plants in cankers or on mummified fruits • In spring this mycelium produces conidia • If mummified fruits are in the soil, fungus produces pseudosclerotia (important for fertilization) that in spring produce apothecia producing asci and ascospores • Conidia and ascospores can infect blossoms and are carried by wind or insects, and are splashed by rain • Although all flower parts except the sepals are susceptible to infection by M. fructicola, only infection of the stamens leads to the development of blossom and twig blight. • It can also cause small cankers on young twigs, but twigs lesions apparently do not produce spores. • Temperature and wetness duration have effect on prevalence of infection • Conidia serves as inoculum later in the season on fruit, where they penetrate via wounds, rarely directly • Fruit are mummified by mycelium growth and are resistant to degradation by soil microorganisms • Mycelium can also infect ripen fruit when in contact with diseased ones.

Armillaria root rot Disease development

• The fungus persist in diseased trees and decaying roots of old stump (saprophytic phase) • Direct root contact and rhizomorphs are responsible for tree to tree spread • Pieces of rhizomorphs or of infected tree material can be moved to new areas by contaminated equipment • Saprobic growth involves indeterminate growth through the forest. Resulting clones can cover many hectares, perhaps even miles, and be thousands of years old. • Healthy trees are less attacked by the fungus

Mycotoxins

• The major toxin produced by F . graminearum in association with FHB in wheat and barley is deoxynivalenol (DON). • DON pose a serious threat to human and domestic animal health. Grain that has been infected with the fungus may become incorporated into our staple diets. Strains of the fungus from different countries produce different toxins, some potentially more potent and dangerous than those from strains currently in the United States. • DON is sometimes called vomitoxin because of its deleterious effects on the digestive system of swine and other monogastric animals. DON disrupts normal cell function by inhibiting protein synthesis. Humans consuming flour made from wheat contaminated with DON will often demonstrate symptoms of nausea, fever, headaches, and vomiting. • DON contamination is measured in parts per million (ppm). DON levels in FHB-infected wheat are frequently quite high (>20 ppm). The USDA recommends that DON levels in human foods not exceed 1 ppm. However, individual grain buyers may have lower tolerances of DON in purchased grain. The FDA has various guideline levels of DON permissible in livestock feed: ruminant animals, such as feeder cattle, are the most tolerant, while swine have the highest sensitivity to DON in livestock feed, with pigs refusing feed containing 1ppm of DON.

rust prediction

• The source of inoculum can be predicted from the pattern of the rust disease. If inoculum comes from barberry, a point source, the resulting disease pattern is usually fanshaped with the alternate host at the apex of the fan • If disease has a more uniform pattern, the inoculum source is usually from a broad area, such as the southern wheat crops (in the northern hemisphere) from which urediniospores are released. Scattered infections mainly on the top leaves in a wheat field indicate that airborne spores were carried into the field from an external source. Rainfall is important for spore deposition during long distance dispersal of the spores. • If disease develops in individual foci within a wheat field, the source of urediniospores is probably overwintering mycelia and/or uredinia. Rusted plants in foci from overwintering sources have heavy infection in lower leaves and less infection in the younger leaves formed higher on the wheat plants.

Armillaria root rot disease control

• Usually it is not attempted in forests • Armillaria species may survive for up to 50 years or more in stumps, depending on the climate, size of stump, and other factors. Removal of dead stumps and avoidance of wounds can contain the disease. This is called Inoculum Reduction - Small roots stay in the soil, but the fungus won't last long in them • In orchards soil can be fumigated before planting and trenching can be used to isolate infected roots • Resistant Species -Planting or favoring the more resistant species will avoid the disease. Larch, birch and to lesser degree ponderosa pine are resistant. Following a rotation with resistant species, the pathogen should have died out in the old root systems, permitting the reestablishment of susceptible species. • Increasing Host Vigor - This is applicable in cases where the disease is linked to prior stress. Examples might be control of defoliating insects; using good planting practices to avoid deformed roots or using seeds. • Biological control. Competing fungi.

Rhizoctonia solani Control

• Very difficult • Drainage control, plenty of aeration are essential for healthy growth • Use clean seeds • Use raised beds for seedlings • Use sterilized soil, solarization or anaerobic disinfestation • Use a three years rotation to combat specific races • Fungicides are generally efficacious on turfgrasses but not on vegetables • Parasitic nematodes, fungi, viruses, myxobacteria can be used as biocontrol agents • Use of resistance rootstocks

Wood rots and decay

• Wood rotting basidiomycetes cause huge losses of timber trees in forests and harvested wood • Living trees usually are damaged only in the heartwood • Cut trees are also damaged in the sapwood • Roots can also be attacked • Note that some ascomycetes such as Diplodia and Alternaria can also cause soft rots

In warm climates

• wheat is planted in late fall and harvested in early summer. • The first spores to infect the young wheat plants in the fall are urediniospores. They generally come from infected volunteer wheat plants. These plants can become infected from spores produced on latematuring wheat plants still in the field. The infected volunteer wheat plants serve as a bridge that carries P. graminis f. sp. tritici through the summer to the next fall-sown crop of wheat.

In regions with temperate climates

• wheat may be planted either in the fall (winter wheat) or the spring (spring wheat) depending on the severity of the winters. • The first rust spores to infect wheat in the spring in temperate regions may be aeciospores from barberry, the alternate host, or urediniospores from infected wheat in distant regions with milder winters.