Potato Late Blight Preview Clip

Summary

The video explains how potato late blight, caused by Phytophthora infestans, can originate even from certified seed tubers that appear healthy. The pathogen can remain latent within tubers, spreading to sprouts as they germinate. Initial plant symptoms, such as brown lesions at the stem base and leaf axils, appear weeks later, often worsening in humid conditions. Leaf lesions may show necrosis with whitish fungal growth on the underside, where sporangia—the pathogen’s asexual reproductive structures—form. Even a few infected plants can trigger an epidemic, with continuously humid weather accelerating the disease's spread, emphasizing the challenges of managing late blight in potato crops.

Takeaways

• 😀 Phyto epidemics in potatoes can occur even with certified seed due to latent infection in the tubers.
• 😀 The late blight pathogen (Phytophthora infestans) can grow inside infected seed tubers, appearing healthy on the outside.
• 😀 Infected tubers begin to show symptoms when they germinate, with the pathogen growing into the sprouting shoots.
• 😀 If the infection is mild, plants may survive without visible signs of the pathogen initially.
• 😀 Symptoms of infection appear after a few weeks, starting with brown lesions at the base of the stem and leaf axils.
• 😀 The pathogen spreads especially in humid conditions, where dew formation encourages its growth.
• 😀 Small brown lesions form on potato leaves, often with chaotic borders, and expand in humid weather.
• 😀 The underside of infected leaves typically shows whitish growth of the pathogen, consisting of sporangia.
• 😀 Sporangia are asexually formed reproductive organs of Phytophthora infestans and are crucial for spreading the disease.
• 😀 A few infected potato plants can lead to a widespread epidemic under continuous humid conditions.
• 😀 Favorable weather conditions for the pathogen include high humidity, which promotes rapid spread of the disease.

Q & A

What is the pathogen responsible for late blight in potatoes?

The pathogen responsible for late blight in potatoes is Phytophthora infestans.

Can certified seed potatoes still carry the pathogen?

Yes, even certified seed potatoes can have individual tubers that are latently infected with Phytophthora infestans.

What does 'latently infected' mean in the context of potato tubers?

Latently infected means that the pathogen is present inside the tuber but the tuber appears healthy on the outside.

How does Phytophthora infestans spread when an infected tuber begins to sprout?

When an infected tuber sprouts, the pathogen grows into the emerging shoots, potentially infecting the entire plant.

What are the first visible symptoms of late blight on potato plants?

The first visible symptoms are brown lesions at the base of the stem and in the leaf axils.

Why do lesions often appear in leaf axils?

Lesions appear in leaf axils because overnight dew provides a humid environment that encourages pathogen growth.

What do the leaf lesions look like, and how do they progress?

The leaf lesions are small, brown, and often have irregular or chaotic borders. In humid conditions, these necrotic areas expand rapidly.

What structures form on the underside of infected leaves, and what is their function?

Whitish growths consisting of dense branched hyphae and sporangia form on the underside of infected leaves. The sporangia are asexual reproductive organs that help the pathogen spread.

How many infected potato plants are needed to start an epidemic?

Only a few infected plants are sufficient to initiate an epidemic of late blight.

What environmental condition favors the rapid spread of Phytophthora infestans?

Continuous humid weather favors the rapid growth and spread of Phytophthora infestans.

What role does the pathogen play inside the tuber before symptoms appear?

The pathogen grows between starch cells inside the tuber without causing visible damage until the plant sprouts and symptoms develop.

What are sporangia and what do they look like?

Sporangia are asexual reproductive structures of Phytophthora infestans, typically lemon-shaped, and formed on the tips of branched hyphae.