Chlorophyll content and chlorophyll stability index in relation to shoot biomass under water stress in cowpea (Vigna unguiculata L.)

Photosynthetic pigments including chlorophyll-a, chlorophyll-b and carotenoids are necessary for photosynthesis. The absolute content as well as ratio of chlorophyll-a and chlorophyll-b and its stability in plants has been used as an indicator of response to stress conditions. In the present study, 20 cowpea genotypes were evaluated for estimation of chlorophyll-a and chlorophyll-b and its stability and correlation with shoot biomass. Under irrigated conditions chlorophyll-a had a mean value of 11.15 while as under drought conditions it had a mean value of 9.01. Similarly, the highest value for chlorophyll-b under irrigated conditions was 37.89 and the lowest value recorded was 16.68 while as under drought conditions the highest value recorded was 35.83 and the lowest value was recorded as 12.57. Under irrigated conditions chlorophyll a/b ratio had a mean value of 0.46 with the while as under drought conditions it had a mean value of 0.48. The chlorophyll stability index (CSI) had a mean value of 0.611 with the highest value recorded for C13 (0.995) followed by SCP-1 (0.979) and C8 (0.979) and the lowest value was recorded for C5 (0.477) followed by C22 (0.54) and C29 (0.58). Shoot biomass was positively correlated with CSI (r=0.593) followed by Chlorophyll-a (r=0.280). CSI was positively correlated with Chlorophyll-a (r=0.598) and Chlorophyll-b (r=0.446). In view of substantial natural variation and significant association with shoot biomass, chlorophyll content and its stability can be used as a reliable surrogate trait for indirect selection for water limited environments.