Groundnut (Arachis hypogaea L.) is an important food and cash crop grown mainly in semi-arid tropics (SAT) regions of the world where drought is the major constraint on productivity. With the aim of understanding the genetic basis and identification of quantitative trait loci (QTL) for drought tolerance, two new recombinant inbred line (RIL) mapping populations, namely ICGS 76 × CSMG 84-1 (RIL-2) and ICGS 44 × ICGS 76 (RIL-3), were used. After screening of 3,215 simple sequence repeat (SSR) markers on the parental genotypes of these populations, two new genetic maps were developed with 119 (RIL-2) and 82 (RIL-3) SSR loci. Together with these maps and the reference map with 191 SSR loci based on TAG 24 × ICGV 86031 (RIL-1), a consensus map was constructed with 293 SSR loci distributed over 20 linkage groups, spanning 2,840.8 cM. As all these three populations segregate for drought-tolerance-related traits, a comprehensive QTL analysis identified 153 main effect QTL (M-QTL) and 25 epistatic QTL (E-QTL) for drought-tolerance-related traits. Localization of these QTL on the consensus map provided 16 genomic regions that contained 125 QTL. A few key genomic regions were selected on the basis of the QTL identified in each region, and their expected role in drought adaptation is also discussed. Given that no major QTL for drought adaptation were identified, novel breeding approaches such as marker-assisted recurrent selection (MARS) and genomic selection (GS) approaches are likely to be the preferred approaches for introgression of a larger number of QTL in order to breed drought-tolerant groundnut genotypes.

• Transpiration efficiency (TE) has been a major target for improved groundnut yield under water stress, TE being mostly proxied with surrogates. • Here TE was measured gravimetrically in lysimeters and did not correlate with surrogates. • TE explained yield differences under high VPD, but not under low VPD. • Stomatal regulation under high VPD may explain part of the large TE differences. • This opens new opportunities to breed improved groundnut for high VPD conditions.

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.