Heritability of Carbon Isotope Discrimination and Correlations with Earliness in Cowpea

Abstract

Drought is a major constraint limiting rainfed crop production in semiarid regions. Selection criteria for increasing transpiration efficiency (TE) may be useful for enhancing drought adaptation. Carbon isotope discrimination (∆) has been negatively correlated with TE in cowpea [Vigna unguiculata (L.) Walp.] and several other C3 species. However, the realized heritability of ∆ is not known and ∆ has shown negative associations with days to flowering, which could limit its usefulness as a selection criterion for enhancing drought adaptation. Field studies were undertaken to estimate the heritability of ∆, estimate the genetic correlation between ∆ and earliness, and determine the response to selection for high and low ∆ and for earliness and lateness in two cowpea populations. Broad‐sense heritabilities were low to intermediate (0.27 and 0.58) for ∆ and high (0.72 and 0.80) for days to first flower (DFF). Selections were made among individual F2 plants, and selected progenies were evaluated as F3 and F4 families. Realized heritabilities were low for ∆ (0.25–0.31) but significant and high for DFF (0.89–0.96). Selecting individual F2 plants for high and low ∆ was effective in identifying F3 and F4 families with high and low ∆ only in one of the crosses. Genetic correlations between ∆ and earliness were negative and low to intermediate in magnitude (−0.14 to −0.66). Selection for earliness can be effective in the F2 generation, but it may result in some indirect selection for high ∆ and, therefore, low TE. Selection for low ∆ may be most efficient with advanced families.