Effects of mild drought stress on the morpho-physiological characteristics of a bambara groundnut segregating population

Bambara groundnut (Vigna subterranea (L) Verdc.) is a drought tolerant underutilised indigenous African legume. The present study aimed to examine the response of bambara groundnut under increasing drought stress and the effects of cumulative mild drought on final yields. The components of morpho-physiological traits were measured for a small F5 breeding cross of bambara groundnut exposed to progressive mild drought in controlled-environment tropical glasshouses. Drought stress reduced stomatal conductance significantly (F(1,130) = 2259.59, p < 0.01), with variation observed between lines of the segregating population (F(64,130) = 16.27, p < 0.01). Higher stomatal density and reduced leaf area were observed in drought treatment plants (p < 0.01). Mild drought stress negatively influenced 100-seed weight (F(1,258) = 19.4, p < 0.01) and harvest index (F(1,258) = 12.87, p < 0.01) by 8 and 15.6 %, compared to the control irrigated treatment, respectively. Bambara groundnut used a combination of mechanisms to tolerate drought stress, including stomatal regulation of gas exchange, reduction of leaf area and maintenance of a relatively high leaf water status and relatively high levels of photosynthesis. Strong genotypic variation observed for many traits in the F5 segregating population allows individual lines with potentially greater tolerance for drought, combined with higher yielding characteristics, to be selected for future breeding programmes in bambara groundnut.