Relationship between resistance to root-knot nematode (Meloidogyne spp.) and cortex layer in tobacco (Nicotiana tabacum L.)

Abstract

Bidi tobacco (Nicotiana tabacum L.) is an important cash crop of India not only for farmers but also for the national exchequer and for generating employment. Root-knot is a major disease of tobacco, causing enormous loss in production. In India the disease was reported on all tobacco types grown in light soils of Gujarat, Karnataka and Andhra Pradesh. Gujarat is one of the major states producing bidi tobacco in India. Assuming that the nematode resistant/tolerant lines of tobacco possess some anatomical peculiarity in roots, which might be deterring the larvae from entering the inner layers. The deterrents could be either a thick hypodermis cell layer or number of cortical cell layers or combinations of both. In this context, a study to determine the mechanism of nematode resistance and to establish the relationship between number of cortex cell layers, which provides the thickness strength to the roots for resistance were initiated. The present findings revealed that there was highly significant negative correlation (-0.52 and -0.37) between number of hypodermis layers and root-knot index as well as total cortex layers and root-knot index, respectively. This suggests that number of hypodermis layers in roots increases the root-knot nematode resistance in tobacco.