PCA PLANT PATHOGENS EXAM ALL QUESTIONS AND CORRECT ANSWERS NEWEST EXAM GRADED A+ 2025

Plant Disease Definition - -Abnormal physiological processes caused by a causal pathogen Economic significance of plant diseases - -Losses of yield, crops, inputs, land Pathogen - -Causal agent of disease Signs of disease - -Structures of the pathogen Symptoms of disease - -Plant response to pathogen infection Abiotic factors of plant disease - -Air pollution, temperature, nutrients Biotic factors of plant disease - -Living organisms (fungi, bacteria, viruses) Obligate parasite - -unable to grow outside of a living host Facultative saprophyte - -prefers living organic matter as a source of nutrition but can adapt to the use of dead organic matter under certain conditions Facultative parasite - -A pathogen that prefers dead inorganic material, but can also obtain nourishment from living organic material Biotroph - -Any parasite that cannot survive in a dead host and therefore keeps it alive Necrotroph - -Parasite that kills host cells Koch's Postulates - -series of guidelines used to identify the microorganism that causes a specific disease Three components of disease triangle - -Causal agent, environment, host Role of each component of disease triangle - -All three must be present for disease to occur. Environment must favor causal agent. Host must favor causal agent. How humans impact each component of disease triangle - -Manipulate the environment, host-plant resistance, preventative/suppressive/erradicative pesticides Impact of epidemic when one component of disease triangle does not come into contact with the other two components - -Slows epidemic to a halt. Disease spread needs all three components interacting Management strategy to break environment component - -Alter planting dates, remove alternative hosts, alter harvest Management strategy to break host component - -Alternate crop, host-plant resistance Management strategy to break causal agent component - -Pesticide applications How can knowledge of plant disease triangle be used in diagnosis? - -Can rule out different pathogens based on host and environment. Epidemiology - -Branch of medical science concerned with the incidence, distribution, and control of diseases that affect large numbers of people. Environmental factors that affect epidemics - -Temperature, humidity, moisture, soil pH, nutrient availability, air movement Importance of time in the development of an epidemic - -Epidemics develop very quickly if conditions are favorable. It is critical to reduce the rate of infection during susceptible life stages of the plant How does type of reproduction cycle affect development of an epidemic - -Polycyclic epidemics can develop much more rapidly than monocyclic epidemics because of secondary inoculum production. How does dissemination affect development of an epidemic - -Conditions that increase dissemination will accelerate development of epidemics Monocyclic disease - -Disease that only has a primary infection cycle Polycyclic disease - -Disease that produces a secondary inoculum, and has a secondary infection cycle in addition to a primary infection cycle Why are monocyclic diseases less likely to result in serious epidemics? - -Controlling primary inoculum is much easier than controlling primary and secondary inoculum. Once primary inoculum is controlled and dissemination is controlled, the disease essentially stops developing. How do sanitation practices impact monocyclic diseases? - -Epidemic may be delayed, but severe epidemic can still occur if environmental conditions are favorable for disease development How do sanitation practices impact polycyclic diseases? - -Reducing primary inoculum may reduce the amount of secondary inoculum produced. If rate of infection is high, there is little effect. But if rate of infection is low, it may reduce an epidemic Formae specialis - -Indicates a fungus is adapted to a specific host Incubation period - -interval between initial infection and first signs and symptoms Infection - -Invasion of a plant by a pathogen Infestation - -Large numbers of pathogen present causing damage Inoculum - -Infecting agent of a pathogen Latent infection - -infection in which the infectious agent is present but not causing symptoms Mummy - -Dead, shriveled fruit that a pathogen may overwinter in Overwintering - -the process by which some organisms pass through or wait out the winter season Pathovar - -subdivision of a plant pathogenic bacterial species defined by host range Propagule - -Portion of a plant which is used to generate a new plant Race - -Strain of a virus adapted to a specific host Soil inhabitant/soil resident - -Pathogen that can survive in the soil for long periods of time Soil transient/soil invader - -Pathogen that can survive in the soil for a short period of time Vector - -An organism that can transport and transmit a disease Apothecium - -cup-shaped ascocarp Ascocarp - -Fruiting body of an ascomycete Ascospore - -sexual spores of ascomycete fungi that develop within an ascus Basidiospore - -A sexual fungal spore produced in a basidium, characteristic of the basidiomycetes Chlamydospore - -a thick-walled, asexual, resistant spore; a survival spore Cleistothecium - -Closed ascocarp, typical of powdery mildews, also known as the Chasmothecium Conidium - -an asexually produced fungal spore formed on a conidiophore, produced in ascomycetes Fungi Imperfecti - -large and heterogeneous form division of fungi comprising forms for which no sexually reproductive stage is known, also known as Deuteromycetes Fungus - -Saprophytic and parasitic spore-producing eukaryotic organisms that lack chlorophyll and include molds, rusts, mildews, smuts, mushrooms, and yeasts. Haustorium (Haustoria) - -specialized hypha of parasitic fungi that grows into a host's tissues and absorbs its nutrients Hypha - -one of many long, slender filaments that makes up the body of a fungus Mycelium - -densely branched network of the hyphae of a fungus Oospore - -thick-walled, sexually derived resting spore of oomycetes Perithecium - -flask-shaped ascocarp Pycnidium - -An asexual hollow fruiting body lined inside with conidiophores. Sclerotium - -Modified fungal hyphae that form a compact and hard vegetative resting structure with a thick pigmented outer rind. Spore - -A reproductive cell of fungi with a hard, protective coating teliospore - -a spore found in rusts and smuts, produced in a telium; functions as a resting spore, and then undergoes nuclear fusion, found in basidiomycetes Zoospore - -Asexual spores of Oomycetes with flagella that can swim Characteristics of Fungi - -Eukaryotic, have sexual and/or asexual reproduction, do NOT photosynthesize, have resistant survival stages, have a vegetative mycelium state, propagules are spores, need free moisture and high humidity for infection How are fungi isolated and identified? - -Grown on pure culture media and identified by their fruiting bodies and spores Plasmodiophora brassicae - -Clubroot Clubroot class - -Plasmodiophoromycetes Clubroot life cycle - -Sexual structure: oospores from antheridium Asexual structure: Zoospores from sporangium Survival structure: Oospores Host range: Most common brassica crops Clubroot symptoms and signs - -Stunted and wilted plants, galls on roots, Oospores can be observed Clubroot Management - -Destroy infected roots, soil pH 7.2 or higher inhibits spore germination, rotate crops, genetic resistance Rhizopus sp. - -Soft rot Soft rot class - -Zygomycetes Clubroot biology - -Obligate parasite Soft rot biology - -Saprophyte Soft rot life cycle - -Sexual structure: zygospores from compatible hyphae Asexual structure: sporangiospores from sporangium Resistant survival stage: mycelium or spores on organic matter Host range: Broad, notably strawberries, sugarbeet, peach, nectarine Soft rot signs and symptoms - -White mycelium, black sporangia, leaking fruit, weak fruit Soft rot management - -Field sanitation, rapid cooling of fruit postharvest Phytophthtora sp. - -Late blight of potato Late blight of potato class - -Oomycetes Late blight of potato biology - -Obligate parasite Late blight of potato life cycle - -Sexual structure: oospores from antheridium Asexual structure: zoospores from sporangia Resistant survival stage: plant debris Host range: broad, but notably potato and tomato Pythium sp. - -damping-off Damping-off class - -Oomycetes Damping-off biology - -Saprophyte Damping-off life cycle - -Sexual structure: oospores from antheridia Asexual structure: zoospores from sporangia Resistant survival stage: found in soil Host range: floricultural crops, cotton, cucurbits Signs and symptoms of Damping-off - -Wilting and root rot Damping-off control - -Fungicides, planting timing, well-drained soils Bremia sp. - -Downy mildew of lettuce Downy mildew of lettuce class - -Oomycetes Downy mildew of lettuce biology - -Biotroph Downy mildew of lettuce life cycle - -Sexual structure: oospores in plant tissue Asexual structure: sporangia formed on sporangiophores, some produce zoospores Resistant survival stage: oospores Host range: lettuce Downy mildew of lettuce signs and symptoms - -White/purple sporulation, yellowing/necrosis on leaves, stunting, malformation Downy mildew of lettuce control - -Fungicides, try to reduce moisture Oomycetes of importance - -Phytophthora sp., Pythium sp., Bremia sp. Erysiphe necator - -Grape powdery mildew Grape powdery mildew class - -Ascomycetes Grape powdery mildew biology - -Obligate parasite Grape powdery mildew life cycle - -Sexual structure: Ascospores Asexual structure: Conidia Resistant survival stage: Mycelium in buds or chasmothecia Host range: Grapes Grape powdery mildew signs and symptoms - -Chlorotic spots, webby mycelium, powdery masses on fruit, blotchy canes, black to brown web scarring Grape powdery mildew control - -Preventative fungicides Taphrina sp. - -Peach leaf curl Peach leaf curl class - -Ascomycetes Peach leaf curl biology - -Biotroph Peach leaf curl life cycle - -Sexual Structure: ascospores Asexual structure: bud-conidia Resistant survival stage: ascospores and bud-conidia on trees in summer Host range: Peach and nectarine Peach leaf curl signs and symptoms - -Discolored leaves, thick stunted distorted shoots, curling leaves Peach leaf curl management - -Resistant cultivars, fungicide treatments Venturia sp. - -Apple scab Apple scab class - -Ascomycetes Apple scab biology - -Necrotroph Apple scab life cycle - -Sexual stage: ascospores from pseudothecia Asexual structure: conidia Resistant survival stage: overwinters in fallen apple leaves Host range: apple, crabapple Apple scab symptoms and signs - -Lesions on leaves and flowers, scabs on apples, defoliation and cracked/deformed fruit Apple scab management - -Resistant cultivars, fungicides, removal/destruction of fallen leaves Colletotrichum acutatum - -Strawberry anthracnose Strawberry anthracnose class - -Ascomycetes Strawberry anthracnose biology - -Necrotroph Strawberry anthracnose life cycle - -Sexual structure: ascospores Asexual structure: conidia Resistant survival stage: Appressoria Host range: Wide Strawberry anthracnose signs and symptoms - -petiole, runner, fruit lesions, stunting and yellowing of plants, sometimes wilting and collapse Strawberry anthracnose management - -Fumigation, solarization, sanitation, fungicide dips, reduce splashing water Sclerotinia sp. - -Watery soft rot, cottony rot Watery soft rot class - -Ascomycetes Watery soft rot biology - -Necrotroph Watery soft rot life cycle - -Sexual structure: ascospores Asexual structure: conidia Resistant survival stage: Sclerotia Host range: wide Watery soft rot signs and symptoms - -soft brown watery rot, plant wilt, white mycelia, black sclerotia Watery soft rot management - -Crop rotations, avoid excess moisture, destroy infected plant debris Monilinia sp. - -Brown rot Brown rot class - -Ascomycetes Brown rot biology - -Necrotroph Brown rot life cycle - -Sexual structure: ascospores from apothecia Asexual structure: conidia from mummies Resistant survival structure: Apothecia from mummies Host range: wide host range Brown rot signs and symptoms - -Blight, gum exudation, cankers on blighted twigs, spore masses, mummified fr