Plant Pathology Exam Review

These flashcards cover major concepts in plant pathology including important diseases, their life cycles, environmental conditions favoring their growth, management strategies, and key differences in resistance mechanisms.

What is Sclerotinia Stem Rot and its primary impact?

Sclerotinia Stem Rot (Sclerotinia sclerotiorum) is a disease affecting over 400 hosts, leading to major yield loss in crops like canola and pulses when infection occurs early in flowering.

Describe the Sclerotinia stem rot disease cycle.

Sclerotia overwinter in soil, germinate into apothecia when conditions are moist, and release ascospores that infect petals and subsequently cause stem infections.

What environmental conditions favor Sclerotinia stem rot development?

Prolonged moisture, cool-to-moderate temperatures, and dense canopies that trap humidity.

What management strategies are effective for Sclerotinia stem rot?

Application of fungicides at 10% bloom, petal tests, risk maps, and using historical field records.

What is Fusarium Head Blight (FHB) and why is it significant?

FHB, caused primarily by F. graminearum, is significant because it reduces the yield and quality of grains such as wheat, barley, and corn, and produces the harmful mycotoxin DON.

Explain the disease cycle of Fusarium Head Blight.

FHB is a residue-borne disease where spores are released during cereal flowering and infect when humidity lasts for at least 12 hours at temperatures between 16-30°C.

What are the symptoms of Fusarium Head Blight?

Symptoms include bleached spikelets, shriveled chalky kernels, and salmon-colored spore masses.

What is Stripe Rust and its causative agent?

Stripe rust (Puccinia striiformis f.sp. tritici) is a polycyclic basidiomycete known for its rapid epidemic potential.

Identify the environmental conditions that favor Stripe Rust growth.

Stripe Rust prefers cool (7-12°C) and humid weather.

What is the difference between qualitative and quantitative resistance?

Qualitative resistance involves a single R gene and is typically non-durable, while quantitative resistance involves multiple genes, providing partial and more durable protection.

What is the disease triangle?

The disease triangle includes a host, a pathogen, and a favorable environment, and all three components must be present for a disease to occur.

What happens when fungicides from Group 11 are used on FHB?

Group 11 fungicides can increase DON levels in grain because they inhibit fungal respiration, which can stress the Fusarium and lead to increased toxin production.

Describe the significance of sclerotia in Sclerotinia sclerotiorum.

Sclerotia are hardened fungal survival structures that can persist in the soil and germinate under favorable wet conditions to produce infections.

What is the role of environmental monitoring in disease management?

Environmental monitoring helps assess risk levels for diseases like FHB through weather-dependent risk indices and petal tests to predict infection likelihood.

How does early seeding contribute to the management of rust diseases?

Early seeding helps crops flower before peak rust spore arrival, thus reducing the risk of infection from pathogens like Stripe Rust.

Why is crop rotation important in managing plant diseases?

Crop rotation helps break the disease cycle of residue-borne and soil-borne pathogens by removing their host plants from the field for a period.