Question

The disease root-knot of brinjal is caused by
A) Fusarium udum
B) Phytophthora infestans
C) Meloidogyne incognita
D) Pseudomonas rubrilineans
E) Xanthomonas citri

Answer 1

Hint: Causal organisms are host specific and disease is transmitted through soil. It is known as “root-knot nematode” - RKN or “southern root-nematode” or “cotton root-knot nematode”. The disease is affected and symptoms were observed in the root of the plant.

Complete answer:
Fusarium udum is the most important soil-borne disease of pigeon pea throughout the world. Phytophthora infestans is the causal organism of late blight disease of potato and tomato. Meloidogyne incognita is a endoparasitic nematode also called as root-knot nematode and its host range is also very large including Solanaceae (e.g. brinjal), Cucurbitaceae (e.g. cucumber) Leguminosae (e.g. pea), Cruciferae (e.g. cabbage), and several other roots and bulb crops (e.g. onion). Pseudomonas rubrilineans cause stalk rot disease in sugarcane. Xanthomonas citri is a bacterial pathogen that causes citrus canker in citrus trees like lime, oranges and grapefruit.

Additional information:
Meloidogyne incognita is a plant-parasitic roundworm in the family Heteroderidae. This nematode has numerous hosts and is one of the four commonest species worldwide.
Meloidogyne incognita exists in soil in areas with hot climates or short winters.
Four major species of Meloidogyne are major pests worldwide such as M. javanica, M. arenaria, M.incognita and M. hapla.
The root-knot nematode larvae infect plant roots and cause the development of the root-knot galls which drain the plant's photosynthate and nutrients. This large, irregular galls on roots are the results of parasitism.
Prevention measures are to pull up all nematode-infested plants and destroy them after the season.

So, the correct answer is ‘Meloidogyne incognita’.

Note: Root-knot nematode symptoms on plant roots are dramatic. Because of nematode feeding, large galls or "knots" can form throughout the root system of infected plants.