Question

Choose the correct answer from the options given below:
(A) Magnaporthe is a pathogen on dicot only
(B) Puccinia is a pathogen on monocot only
(C) Ralstonia is a pathogen on dicot and monocot
(D) RNA virus is a pathogen on dicot and monocot only

• A. (A), (B), (C) only
• B. (A), (B), (C), (D)
• C. (B) and (A) only
• D. (C) and (D) only

Hint:

To remember host specificity:
- *Ralstonia solanacearum* is famous for having one of the widest host ranges among plant pathogens, infecting hundreds of species across both monocots and dicots.
- Heteroecious rusts (*Puccinia*) require both a monocot (cereal) and a dicot (alternative host) to complete their macrocyclic life cycle.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
This question focuses on the host range and host specificity of different groups of plant pathogens.
Pathogens can be host-specific (restricted to monocots or dicots) or have wide host ranges that cross these major taxonomic divisions.

Step 2: Detailed Explanation:
Let us analyze each statement individually:
Statement (A): "Magnaporthe is a pathogen on dicot only"
This statement is incorrect.
Magnaporthe oryzae is the causal agent of rice blast, which is a major disease of rice (*Oryza sativa*) and wheat (*Triticum aestivum*).
Both of these hosts are monocotyledonous crops.
Thus, *Magnaporthe* is primarily a pathogen of monocots, not dicots.
Statement (B): "Puccinia is a pathogen on monocot only"
This statement is incorrect.
While many *Puccinia* species cause rust on monocots (such as wheat, barley, and maize), they are often heteroecious, requiring two different hosts to complete their life cycle.
For example, *Puccinia graminis* requires barberry (*Berberis vulgaris*), which is a dicotyledonous plant, as its alternate host.
Other species like *Puccinia helianthi* cause rust directly on sunflowers, which are dicots.
Statement (C): "Ralstonia is a pathogen on dicot and monocot"
This statement is correct.
Ralstonia solanacearum is a soil-borne bacterium with an extremely wide host range.
It causes bacterial wilt in dicots (such as solanaceous crops like potato, tomato, and eggplant) as well as monocots (such as banana and ginger).
Statement (D): "RNA virus is a pathogen on dicot and monocot only"
This statement is correct.
Plant RNA viruses, which make up the majority of plant viruses, infect a wide range of hosts across both monocotyledonous and dicotyledonous families (e.g., Tobacco Mosaic Virus, Cucumber Mosaic Virus, Maize Dwarf Mosaic Virus).
Therefore, only Statements (C) and (D) are correct.

Step 3: Final Answer:
Statements (C) and (D) are correct.
This corresponds to Option (D).