Groundnut (Arachis hypogaea) genotypes tolerant to intermittent drought maintain a high harvest index and have small leaf canopy under stress.

Intermittent drought, which varies in intensity, severely limits groundnut (Arachis hypogaea L.) yields. Experiments were conducted to assess root development, water uptake, transpiration efficiency, yield components and their relationships, in 20 groundnut genotypes under well watered (WW), and mild (DS-1), medium (DS-2) and severe (DS-3) intermittent stress. Pod yield decreased 70%, 55% and 35% under severe, medium and mild stress, respectively. Pod yield varied among genotypes, and showed significant genotype-by-treatment effects. Root length density (RLD) varied among genotypes before and after stress, although RLD did not discriminate tolerant from sensitive lines. Total water uptake and RLD under water stress had a weakly significant relationship. Water extraction from the soil profile was highest under severe stress. Water uptake varied among genotypes in all water regimes, but correlated with pod yield under WW conditions. The relative harvest index (HI) (i.e. the ratio of the HI under stress to HI under WW conditions) was closely related to the pod yield in all three intermittent stresses (R2=0.68 in DS-1; R2=0.65 in DS-2; R2=0.86 in DS-3) and was used as an index of stress tolerance. Under medium and severe stresses, the relative HI was negatively related to plant leaf weight (R2=0.79 in DS-2; R2=0.53 in DS-3), but less so under mild stress (R2=0.31). The results suggest that under intermittent stress, genotypes with a lower leaf area may use water more sparingly during the drying cycle with less damaging consequences for reproduction and pod.