Investigations on the root-knot nematode (Meloidogyne incognita) (Kofoid & White, Chitwood) resistance in cowpea (Vigna unguiculata, L.) walp

Abstract

Resistance to M. incognita in cowpea selections IC 9642-B and TVU 2430-P was associated with reduced larval invasion, root galling, egg mass production and fecundity; delayed development of larvae to adult female stage coupled with high concentration of magnesium. Histological studies revealed that was a direct correlation between the number of cork layers and resistance to M. incognita. Cortical sclereids were noticed in resistant selections, while they were absent in the susceptible cultivars. There was more number of starch grains in the cortex susceptible cultivars than in that of resistant selections. Histopathological investigations revealed that there was less number of giant cells which were smaller in size with less number of nuclei in resistant selections as compared to susceptible cultivars. Death of cells (hypersensitive reaction) around infecting M. incognita larvae occurred in the roots of resistant selection IC 9642-B. Histochemical studies revealed that there were more of insoluble polysaccharides, proteins and nucleic acid in susceptible cultivars as compared to the resistant selections of cowpea. Cowpea selections IC 9642-B and TVU 2430-P (resistant to M. incognita were crossed with commercial cultivars S-288 and S-488 (susceptible). The mode of root-knot nematode inheritance in F1’s, F2’s and back cross generations indicated a Mendelian pattern of segregation. The F1 plants were all resistant. The F2 populations segregated as expected assuming monogenic control and complete dominance with resistant and susceptible plants occurring in a 3 to 1 ratio. The back crosses generations of these crosses with the susceptible parents segregated in the ratio of 1 resistant to 1 susceptible. Hence it was concluded that resistance to M. incognita in IC9642-B and TVU 2430-P selections of cowpea is conditioned by a dominant allele at a single locus. 211