Genotypic Variation for Normalized Difference Vegetation Index and Its Relationship with Grain Yield in Cowpea Hybrids Under Drought and Well-Watered Conditions.

Selection for secondary traits with high heritability under drought and strong associations with grain yield has now been adopted as an efficient breeding strategy for drought tolerance which is rather complex with low heritability. The Normalized Difference Vegetation Index (NDVI) is a non-destructive index of plant “greenness” or photosynthetic activity which is considered to be correlated to crop productivity under stress. This study was conducted to estimate the relationship between NDVI with grain yield and other yield related parameters of cowpea at different growth stages (vegetative, flowering and pod-filling). One hundred cowpea crosses developed using North Carolina II mating design were evaluated in two locations under drought stress and well-watered conditions in a 10 x 10 α-lattice design with three replications. Grain yield ranged from 2608kgha-1 under stress under drought stress to 4020kgha-1 under well-watered conditions for the cross between TVu6707 x TV9797. Cowpea crosses varied significantly for NDVI from vegetative to pod-filling stage. However, the higher yielding crosses maintained higher NDVI readings than low yielding types under stress. Result of combined analysis of variance across locations revealed that NDVI measured at pod-filling stage (NDVI_3) had stronger relationship with grain yield, seed per plant and pod per plant than at other growth stages. Positive and highly significant correlation coefficients (R) were recorded for NDVI_3 and grain yield, seed per pod and pod per plant (p <0.0001). R values for grain yield were 0.39 and 0.33 under drought and well-watered conditions respectively, while the values for seed per plant under drought and well-watered were 0.41 and 0.42 respectively. This relationship suggests that NDVI can be a potential selection tools for cowpea grain yield improvement under drought tolerance and that high potential for green biomass accumulation at the seedling stage may be predictive of high grain yielding potential.