Evaluation of salt tolerance in cowpea at seedling stage

Cowpea [Vigna unguiculata (L.) Walp.] is a nutrient-dense diploid legume species (2n=2x=22) that provides protein to human. Its cultivation has provided farmers in various regions of the world with substantial incomes. However, cowpea production can be easily hampered by abiotic stresses such as soil salinity. In this study, we aimed to screen 331 cowpea genotypes from more than 32 countries for their tolerance to salt stress, to investigate potential correlations among various traits investigated for salt tolerance, and to identify salt-tolerant cowpea genotypes. The cowpea genotypes were screened in a greenhouse and were irrigated with deionized water (no salt treatment) and with a solution of 200 mM NaCl (salt treatment). Data on a total of 16 traits including leaf injury score, fresh leaf biomass, and plant height were recorded. Results demonstrated (1) a large variation in salt tolerance among the cowpea genotypes, (2) high correlation between traits such as leaf injury score, leaf SPAD chlorophyll, relative tolerance index for leaf SPAD chlorophyll, and fresh leaf biomass, but no correlation between leaf injury and relative tolerance index for plant height, (3) PI300173, 09-671, PI583209, PI582572, PI293545, PI339587, PI152195, PI582874, 09-529, PI583241, PI583550, PI293486, PI582823, PI293480, PI583237, 09-470, PI582474, PI582878, PI582864, PI583200, PI339603, and PI582469 were found to be salt-tolerant, and (4) country of origins could influence salt tolerance in cowpea. Salt-tolerant and salt-susceptible genotypes were repeated to further validate our results. The results could be used in cowpea breeding programs and allow for cowpea cultivation where soil salinity is predominant.