SEARCH FOR RESISTANCE TO ROOT-KNOT (MELOIDOGYNE INCOGNITA AND M. JAVANICA) AND RENIFORM (ROTYLENCHULUS RENIFORMIS) NEMATODES IN COWPEA

Abstract

Cowpea (Vigna unguiculata) is severely affected by root-knot nematodes, Meloidogyne spp., (Swarup, 1962) and by Rotylenchulus reniformis Linford & Oliveria, 1940 (Seshadri, 1970). R. reniformis causes 13% loss in cowpea yield from farmer’s point of view (Reddy & Singh, 1981). Growing resistant variety is the least expensive way of managing nematode diseases. Several workers have tried to locate resistance source through screening of germplasm in cowpea. Variety V-16 has been reported to be resistant to R. reniformis (Thakar & Patel, 1984). Cowpea varieties C-152 (Patelet al., 1977) and 82-1B (Patel et al., 1984) have been also identified as root-knot resistant cultivars. To further locate the sources of resistance to nematodes, 37 cowpea lines were tested separately against root-knot (mix population of M. incognita and M. javanica) and reniform (R. reniformis) nematodes in 10 cm diameter earthen pots filled with steamed soil. Completely randomized design with 5 replications was used. Variety Pusa falguni, a known susceptible cultivar, was used a check. Single seed of each line was seeded/pot. On attaining 2-3 cm height, 500 second stage juveniles of root-knot and 200 pre-adult larvae of reniform nematodes were inoculated in the rhizosphere of each plant in each set. Plants under root-knot inoculations were examined after 45 days of incubation and roots scaled for root-knot intensity using 0-5 (0=Free, 5-Maximum root galling) rating scale. In case of reniform nematode, 12 days after inoculation, each plant was carefully removed and washed free of soil. Roots were stained in0.05% acid fuchsin lactophenol. Finally the reaction of susceptibility to nematode infection for each variety was given on the basis of maximum gall index for root-knot nematodes and maximum number of females penetrated in the roots for reniform nematode.