Genetic and Genomic Resources to Improve Resilience to Striga [Striga Gesnerioides (Wild.) Vatke] and Drought in Cowpea

Abstract

Cowpea (Vigna unguiculatan (L.) Walp.) is a grain legume cultivated worldwide in over 14 million ha but its productivity in Senegal is seriously affected by the infestation of Striga gesnerioides (Wild.) Vatke, a parasitic weed. Striga resistance is an important trait that is missing to most cultivated varieties in Senegal. Its negative effect on cowpea is exacerbated by drought which is a threat to agriculture. The present dissertation describes various options taken on the improvement of cowpea for Striga resistance and drought tolerance using microsatellite markers and drought tolerance indices and cultivar superiority coefficients. The first breeding activity describes methods and results obtained in identifying farmer concerns and interest on profile of their desired ideotype in Louga, Kebemer and Tivavouane involving 109 farmers. The second breeding activity was conducted in response to Participatory Rural Appraisal (PRA) indication on major constraints to anticipate on pre-breeding in order to identify drought tolerant lines that can be used as parental lines in developing new varieties. This study used phenotypic data recorded from well-watered and water-stressed experimental fields in Bambey (ISRA, CNRA de Bambey) and involved 112 accessions from the Senegalese cowpea breeding programme. The third breeding activity focused on cowpea resistance to Striga gesnerioides using Marker-assisted selection (MAS). The different options deployed involved in MAS were the creation of bi-parental lines of hybrids, RIL populations and advanced backcross populations using Marker-assisted backcrossing (MABC), the validation of resistance of the developed backcross lines in field in natural infestation and the identification of loci associated to Striga resistance in cowpea using Genome-Wide Association Analysis (GWAS) on a wide population composed of 367 unrelated accessions from diverse origins in the word. PRA revealed that drought was the major constraint to cowpea production and farmers were interested in large and brown seeded cowpea grain type in Senegal. Striga was important only in some divisions. Preliminary field and pot screening identified several lines more tolerant to drought compared to best tolerant check Mouride, reliability of markers used in MABC were weak, resistant BC4 lines performed unexpectedly in field in regards to SNP screening predictions. Significant markers were identified in 2 environments out of 4. Six candidate genes were identified in regions neighbouring identified markers and annotated. SNPs identified were not reported before in any article to best of our knowledge. The identified genetic and genomic resources could be used in population development for drought tolerance and S. gesnerioides resistance in cowpea.