Question

Root knot disease of Brinjal/ Tobacco is due to _________
A. Phytophthora infestans
B. Meloidogyne incognita
C. Fusarium udum
D. Xanthomonas citri
E. Pseudomonas rubrilineans

Answer 1

Hint: Some plants have spotted on their leaves, while some are wilted even after a good supply of water and nutrients. Even if proper conditions are present, some plants do not grow properly. This happens due to any kind infection caused in them by the pathogen, which could be a bacteria, virus, fungi etc.

Complete answer:
Like diseases in humans, plants are also attacked by bacterias, viruses: causing them a disease. This can alter their metabolism or affect them morphologically.
What is a root-knot disease? The formation of galls in the roots of the plant is a root-knot disease. Seeds are affected more than the adult plants.
Let us learn about the pathogens in the options.
Option A: Phytophthora infestans: It is a water mould that will cause late blight disease in the potato/ tomato. It is favoured in the moist cool surroundings. It can develop a zoospore at a temperature below 15 degrees.
Option B: Meloidogyne incognita: It is a parasitic nematode. It causes the galls in the roots of brinjal/ tobacco etc plants. These microbes feed on the plant and thus galls are formed.
Option C: Fusarium udum: It is a fungus that is soil-borne and pathogenic. It will cause wilting in the pigeon pea. It destroys about 30-80% of pigeon pea crops throughout the world.
Option D: Xanthomonas citri: It is a gram-negative bacteria causing the citrus canker in plants. It causes leaf spotting. It can also result in shoot dieback or fruit drop in severe conditions.
Option E: Pseudomonas rubrilineans: It is a gram-negative bacterium causing seedling blight and fruit blotch in cucurbits.

So the answer is option B: Meloidogyne incognita.

Note: RNAi is a technique developed to protect the plants from the Meloidogyne incognita species to infect their roots. The host is made transgenic by forming a dsRNA and silencing the mRNA in the nematode. Thus the microbe cannot affect the brinjal/Tobacco now.