Question

Motile infective propagules are produced by
A. Pythium
B. Phytophthora
C. Xanthomonas
D. Ralstonia
E. Nematodes
Choose the correct answer from the options given below:

• A. Pythium and Phytophthora possess pili
• B. Pythium and Phytophthora possess fimbria
• C. Nematodes have flagella
• D. Xanthomonas and Ralstonia possess flagella

Hint:

Bacteria move by Flagella or Pili (twitching).
Oomycetes move by Flagella (on Zoospores).
Nematodes move by Undulatory/Muscular waves.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify the structures responsible for the motility of the listed plant pathogens' infective units.

Step 2: Detailed Explanation:

• Pythium and Phytophthora (A, B): These are Oomycetes. They produce motile spores called zoospores. Zoospores possess two flagella (whiplash and tinsel type) for swimming in water films. However, they do not possess pili or fimbriae, which are bacterial structures.

• Xanthomonas and Ralstonia (C, D): These are Gram-negative, motile bacteria. They move using flagella. Xanthomonas typically has a single polar flagellum, while Ralstonia often has several polar flagella. Their motility is essential for entering the host through natural openings or wounds.

• Nematodes (E): These are microscopic unsegmented worms. While they are highly motile, their movement is achieved through the contraction of longitudinal muscles acting against their hydrostatic skeleton. They do not possess flagella.

• Analysis of Options:
- Option 1 and 2 are incorrect because pili and fimbria are bacterial attachment structures, not eukaryotic motility structures.
- Option 3 is incorrect because nematodes move via muscular waves, not flagella.
- Option 4 correctly identifies that the bacterial pathogens listed use flagella for motility.
Final Answer:
The statement that Xanthomonas and Ralstonia possess flagella is the only factually correct description among the given options.
The correct option is (D).