Abstract
Drought is the major abiotic constraint affecting peanut productivity and quality worldwide. There is a pressing need to improve the water use efficiency (WUE) of rain-fed peanut production. Breeding varieties with higher water use efficiency is seen as providing part of the solution. The objectives of this work were to (i) evaluate genetic variation in WUE, harvest index, root dry weight, specific leaf area (SLA) and SPAD chlorophyll meter reading (SCMR) among peanut genotypes in response to different available soil water levels and (ii) assess the relevance of root dry weight, SLA and SCMR to WUE in peanut under receding soil moisture levels. Two greenhouse experiments were conducted in the dry and rainy seasons in 2002/2003. The 11 peanut genotypes (ICGV 98300, ICGV 98303, ICGV 98305, ICGV 98308, ICGV 98324, ICGV 98330, ICGV 98348, ICGV 98353, Tainan 9, KK 60-3 and Tifton-8) and three soil moisture levels [field capacity (FC), 2/3 available soil water (AW) and 1/3 AW] were laid out in a factorial randomized complete block design (RCBD) with six replications. At 37, 67, and 97 day after sowing (DAS), data were recorded for SLA and SCMR. Root dry weight, harvest index (HI) and WUE were recorded at harvest. Drought reduced WUE, root dry weight and HI. Across both seasons, Tifton-8 and ICGV 98300 had high WUE and also had large root systems under drought conditions. ICGV 98324 and Tifton-8 had low SLA and high SCMR under stressed and non-stressed condition. Under drought conditions, ICGV 98324 had high HI and Tifton-8 had low HI. Root dry weight had a greater contribution to WUE under well-watered and mild drought (2/3 AW). Under severe drought (1/3 AW), SLA showed a more important contribution to WUE than the other traits. Traits that were associated to high WUE under drought conditions were different among different peanut genotypes. ICGV 98300 maintained high root dry weight under 2/3 AW and ICGV 98324 maintained low SLA and high SCMR under 1/3 AW. Tifton-8 had both large root systems and low SLA associated with high WUE.
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