Selection of cowpea (Vigna unguiculata [L.] Walp) accessions resistant to root-knot nematode

Cowpea, Vigna unguiculata, is a legume adapted to regions with a tropical climate and limited water resources, and it has become a basic food source and income generator. Root-knot nematodes (Meloidogyne spp.) cause substantial damage to the root system, resulting in yield losses. Genetic resistance is one of the most efficient management methods. The objective of this study was to generate information on genetic resistance to Meloidogyne incognita and Meloidogyne javanica of Brazilian cowpea genotypes. For this, 18 accessions of cowpea from the collection of Embrapa Meio-Norte and six control accessions of cowpea were tested in completely randomized design with six replications, evaluated 60 days after inoculation, and carried out twice in time. To assess root penetration of nematodes and root gall formation in NIL-CB3-isoline, which allows reproduction but limits gall formation, nematodes inside the roots were stained with acid fuchsin, after inoculation with 5000 J2, with estimates at 72 h time-points up to 28 days. None of the 18 accessions from Embrapa showed resistance to M. javanica, but accessions MNC06-895-1, MNC04-14, MNC06-909-6, 98, MNCO4-907-35, and Am60-15 showed resistance to M. incognita. There was a reduction in the number and size of galls in the NIL-CB3 egg isoline, and an increase in formation of males, which are not important for parasitism. Given the importance and prospects for expansion of the cowpea crop throughout Brazil, the results of this study contribute to the knowledge on the reaction of Brazilian cowpea genotypes to the root-knot nematode.