Seedling salt tolerance for above ground-related traits in cowpea (Vigna unguiculata (L.) Walp)

With poor quality of irrigation water, salt concentrations in cultivated areas keep increasing, hence preventing cowpea from being cultivated for optimal growth and development. Effects of salinity on crops are severe in semi-arid and arid regions where low rainfall does not allow salt compounds to be leached from soils. Seedling stage is one the most vulnerable stages in plant growth and development. However, to date, few if any salt-tolerant cowpea cultivars have been reported worldwide. Therefore, the objective of this study was to evaluate cowpea genotypes for salt tolerance based on the reduction of above ground-related traits. A total of 155 cowpea genotypes was phenotyped for salt tolerance at seedling stage. Salt treatments were 0 mM and 200 mM NaCl. The experiment design was completely randomized (CRD) with three replications per genotype and salt treatment combination, and organized in a split-plot manner. Salt stress was imposed for 2 weeks and a total of 19 parameters were used for salt tolerance evaluation. Results revealed that: (1) a large variation in salt tolerance was found among the 155 cowpea genotypes; (2) salt stress significantly reduced plant height and fresh shoot biomass, but slightly increased chlorophyll content; (3) a relatively high correlation was found between plant height and fresh biomass-related parameters; (4) chlorophyll content had low correlation with plant height and fresh shoot biomass reductions, respectively; and (5) PI354686, PI353270, PI354666, and PI354842 were salt-tolerant based on the decrease in plant height and fresh shoot biomass, and PI548785, PI582466, PI339599, and 09-697 were the top performers based on chlorophyll content. These results can be used for advancing breeding programs for salt tolerance in cowpea.