Selection of phenotypic traits and resistance to Cowpea severe mosaic virus and Cowpea aphid-borne mosaic virus in cowpea [Vigna unguiculata (L.) Walp.] seeds with rugose white coat

Abstract

Cowpea ['Vigna unguiculata' (L.) Walp.] is an important protein source in diets in Brazil. The preference of consumers is for large, white, light brown and evergreen seeds with rugose coat and small hilum and hilum ring. The 'Cowpea severe mosaic virus' (CPSMV) and the 'Cowpea aphid-borne mosaic virus' (CABMV) are the main pathogens in cowpea plantations in Brazil. This study selected cowpea offspring with (i) white rugose coat seed characteristics that are accepted by markets and (ii) that present resistance to CPSMV (serotype I) and CABMV. The first selection of asymptomatic plants was carried out using seedlings from F3 seeds mechanically inoculated with a mixture of the two viruses. Offspring F3:4 went through a second selection process with two stages, one in the field (with natural inoculation), one in trays (with mechanical inoculation). In total, 40 F3:4 offspring were selected to evaluate agronomic traits in two field assays, one in Teresina, one in Tracuateua (states of Piau and Par , respectively) based on a randomized block design with four repetitions. Significant effect of genotype and of the interaction assay x genotype was observed (p <= 0.01) for most of the traits evaluated: weight of 100 seeds, yield, seed length, width, and height; length-to-height ratio; width-to-height ratio, and hilum width-to-length ratio. Fourteen offspring produced large seeds (25 - 30 g in 100 seeds), and four presented cross-resistance to CPSMV and CABMV, while 36 offspring were resistant only to CPSMV.