Identification and marker-assisted introgression of QTL conferring resistance to bacterial leaf blight in cowpea (Vigna unguiculata (L.) Walp.)

Bacterial leaf blight (BLB), caused by Xanthomonas axonopodis pv. vignicola (Xav), is widespread in major cowpea [Vigna unguiculata (L.) Walp.] growing regions of the world. Considering the resource poor nature of cowpea farmers, development and introduction of cultivars resistant to the disease is the best option. Identification of DNA markers and marker-assisted selection will increase precision of breeding for resistance to diseases like bacterial leaf blight. Hence, an attempt was made to detect QTL for resistance to BLB using 194 F2 : 3 progeny derived from the cross ‘C-152’ (susceptible parent) 9 ‘V-16’ (resistant parent). These progeny were screened for resistance to bacterial blight by the leaf inoculation method. Platykurtic distribution of per cent disease index scores indicated quantitative inheritance of resistance to bacterial leaf blight. A genetic map with 96 markers (79 SSR and 17 CISP) constructed from the 194 F2 individuals was used to perform QTL analysis. Out of three major QTL identified, one was on LG 8 (qtlblb-1) and two on LG 11 (qtlblb-2 and qtlblb-3). The PCR product generated by the primer VuMt337 encoded for RIN2-like mRNA that positively regulate RPM1- and RPS2-dependent hypersensitive response. The QTL qtlblb-1 explained 30.58% phenotypic variation followed by qtlblb-2 and qtlblb-3 with 10.77% and 10.63%, respectively. The major QTL region on LG 8 was introgressed from cultivar V-16 into the bacterial leaf blight susceptible variety C-152 through marker-assisted backcrossing (MABC).