Question

Given below are two statements, one is labelled as Assertion (A) and other labelled as Reason (R).
Assertion (A): Active dissemination and infection is observed in flagellated plant pathogens like Phytophthora
Reason (R): Root exudates attract zoospores of Phytophthora
In light of the above statements, choose the correct answer from the options given below:

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Flagellated zoospores of oomycetes like Phytophthora use chemotaxis to swim actively toward host root exudates, which facilitates targeted infection.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Oomycete pathogens, such as Phytophthora species, produce asexual, biflagellated spores called zoospores.
These flagellated spores can swim through water films in the soil or on plant surfaces to locate and infect host tissue.

Step 2: Detailed Explanation:
Let us analyze both statements:
- Assertion (A) is true: Unlike fungal spores that rely entirely on passive dispersal (like wind or rain splash), Phytophthora produces motile zoospores equipped with two flagella (a tinsel flagellum and a whiplash flagellum).
These flagella allow the zoospores to swim actively through soil water toward host plant roots to initiate infection.
- Reason (R) is true: The swimming behavior of zoospores is directed by chemotaxis.
Host plant roots release root exudates containing specific sugars, amino acids, and phenolic compounds.
Zoospores detect these chemical concentration gradients and swim directly toward the root surface, concentrating at target areas like the elongation zone.
Because this chemotactic attraction to root exudates directs the active swimming and facilitates targeted infection of the host root, Reason (R) is the correct explanation of Assertion (A).

Step 3: Final Answer:
Hence, the correct option is (A).