Race specific biochemical responses in differential hosts against the root-knot nematode, Meloidogyne incognita

Investigations on sequential development of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), phenol and lignin-like polymers, were undertaken in differential host plants (cotton cv. Deltapine-16 and tobacco cv. NC-95) along with susceptible hosts (cotton cv. H-777 and tobacco cv. FCV-Special) after inoculation with different host races of Meloidogyne incognita. All the races induced a faster and early accumulation of these defense parameters upon inoculation to host differentials than their healthy controls, whereas race-inoculated susceptible tobacco cv. FCV Special and cotton cv. H-777 showed a gradual and delayed accumulation in their defense reactions, but the per cent increase over their uninoculated controls, was of less magnitude than that observed in host differentials at different time intervals. Further, gel electrophoretic study showed de novo appearance of isozyme only in race-inoculated host differentials. It was evident that virulent and avirulent races were able to induce defense mechanisms with different speed in host differentials. On the basis of interactions observed between races and host differentials at 7 DAI, a biochemical model has been hypothesized for differentiating the four races of M. incognita with respect to phenylalanine ammonia lyase activity.