Effects of exogenous 2,4-epibrassinolide on photosynthetic traits of 53 cowpea varieties under NaCl stress

This study examined the effects of exogenous 2,4-epibrassinolide (EBR) on photosynthetic traits of 53 cowpea varieties under NaCl stress. The results of different analysis and correlation analysis showed that these 53 germplasm resources had rich genetic diversity, and significant correlations existed among various photosynthetic traits. Under NaCl stress, Pn was highly significantly positively correlated with Gs and Tr and extremely significantly negatively correlated with Ci. Under EBR treatment, Pn was extremely significantly positively correlated with Gs, Ci, Tr and it was significantly negatively correlated with Chla, Chlb, Chl(a + b), and Y(II). Under EBR treatment and NaCl stress, Pn was extremely significantly positively correlated with Tr, and significantly positively correlated with Gs and carotenoid reflectance index. Principal component analysis shows that in CK group and EBR treatment group, cowpea photosynthesis traits can be summarized as six principal components, contributing 82.298 and 83.046%, respectively, can replace 19 photosynthetic traits to evaluate 53 cowpea varieties; under NaCl stress group and EBR + NaCl stress group, photosynthesis traits can be summarized as seven principal components, with cumulative contribution rate of 84.564 and 85.742%, respectively. In the untreated case, the cluster analysis was used to screen 32 cowpea varieties exhibiting the strongest photosynthetic capacity. Under salt stress, six of these varieties were classified as salt-tolerant. Under EBR spraying + salt stress, all four varieties showed strong photosynthetic capacity, and EBR showed the best relief of salt stress. The results of this study will provide a theoretical basis for the application of exogenous EBR to alleviate cowpea salt stress damage.