Application of marker-assisted backcrossing to improve cowpea (Vigna unguiculata L. Walp) for drought tolerance

Molecular-assisted backcrossing (MABC) was used to introgress drought tolerance, Striga and rootknot nematode resistance QTLs into a farmer-preferred widely grown cowpea landrace adapted for intercropping in Burkina Faso. Two backcross populations were developed using two drought tolerant donor lines IT93K-503-1 (nematode resistant) and IT97K-499-35 (Striga resistant) and the drought sensi tive landrace Moussa Local as the recurrent parent. A set of 184 genomewide EST-derived SNP markers spanning an average of 2-cM intervals and flanking known trait positions was employed for genotyping the backcross progenies using the cowpea KASP genotyping platform. BC1F1 individual plants that were heterozygous for SNPs associated with drought tolerance, Striga and/or nematode resistance (foreground SNPs) and carried as many recurrent-parent alleles as possible at other SNP loci (background SNPs) were selected for the next backcross cycle. This process was repeated to produce BC3F1 families of each donor population. The six best families from the two donors based on marker aided selection and preliminary yield performance under well -watered and water-restricted field trials and Striga resistance screening were selfed to increase seed (BC3F2) for further yield tests. This study demonstrated the high efficiency of using SNP markers in foreground and background marker selection in a MABC scheme to improve a widely grown cowpea variety by adding drought tolerance and biotic stress resistance traits.