Screening diverse cowpea (Vigna unguiculata (L.) Walp.) germplasm for Callosobruchus chinensis (L.) resistance and SSR based genetic diversity assessment

Globally, cowpeas (Vigna unguiculata (L.) Walp.) rising importance face quality and yield obstacles during their production and storage due to insect pests. Among insect pests, the bruchid (Callosobruchus chinensis L.) is a significant storage pest, causing both quantitative and qualitative losses. Hence, it is the need of the present to assess differential responses and genetic diversity of cowpeas for the identification and deployment of bruchid-resistant cultivars in breeding programs, as the host plant resistance is a better and eco-friendly strategy compared to others. In the present study, a total of 62 accessions from five different cowpea-growing countries viz., India, Philippines, Nigeria, USA, and Brazil were evaluated for their reaction to pulse beetles under 'no choice' artificial infestation conditions. Substantial variations among the accessions were observed for parameters viz., oviposition, adult emergence, mean development period, emergence holes, weight loss and growth index (GI). The GI ranged from 1.604 to 4.768, based on which the accessions were categorized as highly resistant (EC528425, IC201075, EC390268, EC101928), resistant (9 accessions), moderately susceptible (13 accessions), susceptible (12 accessions), and highly susceptible (24 accessions) to attack of C. chinensis. Correlations indicated that the growth index had a significant negative relationship with the mean development period and a significant positive relationship with adult emergence. Regression, biplots, dendrogram and principal component analysis (PCA) were performed to assess the association and reaction of seed and insect growth parameters. Two principal components contributed 71.6% variability in PCA research. While the worked 62 accessions have been grouped into two major clusters according to the resistance reaction of the accessions. Further, an assessment of genetic diversity was done using 26 polymorphic simple sequence repeat (SSR) markers. Of the primers tested, VR016, VR108, VM24 and VR015 were found to be the most informative as shown by their high polymorphism information content (PIC) values.