Test on Plant Diseases: Agents, Diagnosis, Management

Question 1: The primary impact of potato late blight in the 1840s was the widespread destruction of American elm trees.

A. Ano

B. Ne

Explanation: Potato late blight was responsible for widespread epidemics throughout Ireland and Europe, resulting in famine and the emigration of 1.5 million people from Ireland. Dutch elm disease, caused by Ophiostoma ulmi, was responsible for the destruction of American elm trees.

Question 2: Which plant disease is credited with transforming England into a nation of tea drinkers due to its devastating impact on coffee plantations in Ceylon?

A. Potato late blight

B. Dutch elm disease

C. Coffee rust

D. American chestnut blight

Explanation: The study materials state that the fungal disease coffee rust, caused by Hemileia vastatrix, appeared in coffee plantations in Ceylon in the 1860s and destroyed the coffee industry there. As a consequence, tea was planted in its place, leading to England becoming known as a nation of tea drinkers.

Question 3: For Black pod disease to develop in Ghana, the host plant (a susceptible variety of cocoa), the causal factor (the fungus Phytophthora palmivora), and the proper environmental conditions must all be present simultaneously.

A. Ano

B. Ne

Explanation: The study materials state that for Black pod disease in Ghana, the disease triangle consists of the host plant (a susceptible variety of cocoa), the causal factor (the fungus Phytophthora palmivora), and the proper environment. It specifies that when all three of these factors are present, black pod will develop, and if one component is missing, disease will not occur.

Question 4: According to the provided study materials, what is the primary reason for removing mummified fruit from trees or the ground as a disease management practice for conditions like Brown Rot?

A. To enhance the aesthetic appearance of the orchard.

B. To reduce the amount of overwintering inoculum available to infect newly emerging tissues.

C. To provide a nutrient source for beneficial soil microorganisms.

D. To improve air circulation around the developing fruits.

Explanation: The study materials state that removing and destroying mummied fruit, as an example for Brown Rot, 'significantly help to reduce the amount of overwintering inoculum which will be available to infect the newly emerging tissues in the spring.' This practice falls under sanitation, which aims to reduce the potential for spread of biotic agents.

Question 5: Systemic fungicides are primarily effective only when applied before a pathogen has invaded the plant host, without any curative action after invasion.

A. Ano

B. Ne

Explanation: Systemic fungicides have a therapeutic or 'kickback' mode of action, meaning they can kill or inhibit the growth of pathogens even after the pathogens have invaded the plant host. They are absorbed and translocated within the plant, allowing them to act curatively.