Genotypic variability among peanut (Arachis hypogea L.) in sensitivity of nitrogen fixation to soil drying

Peanuts (Arachis hypogea L.) are often grown on sandy soils and drought stress can be a major limitation on yield. In particular, loss in nitrogen fixation activity associated with soil drying might be limiting due to the need for high nitrogen amounts in both vegetative tissues and seeds of peanut. This study examined the response of nitrogen fixation of intact plants of seventeen peanut genotypes when subjected to soil drying in pots over approximately a 2-wk period. A large range in the sensitivity of nitrogen fixation to soil drying was observed among the seventeen genotypes. Genotype ICGV86015, in particular, was found to have nitrogen fixation that was especially tolerant of soil drying. Significant positive (P<0.0001) correlation was found between the soil water content at which nitrogen fixation began decreasing and the amino acid concentration in the leaves of severely stressed plants

Genotypic variation in peanut for transpiration response to vapor pressure deficit

Conservation of soil water resulting from decreases in stomata conductance under atmospheric high vapor pressure defi cit (VPD) conditions is a possible approach for enhanced tolerance of water defi cit by crops. Water defi cit is usually a concern in peanut (Arachis hypogea L.) since it is frequently grown on sandy soils with low water-holding capacity. Seventeen peanut genotypes were studied to determine the response of their transpiration rates (TR) to VPD. The results of this study demonstrated variation among peanut genotypes with nine genotypes exhibiting a breakpoint in their VPD response at about 2.2 kPa, above which there was little or no further increase in TR. Therefore, these genotypes with a breakpoint have the possibility of soil water conservation when VPD exceeded 2.2 kPa. The remaining eight genotypes had a linear response in TR over the whole range of tested VPD. Also, the 17 genotypes could be separated into groups with differing rates of increasing TR at low VPD. The change in TR with increasing VPD may be important in determining the rate at which soil water is used under fi eld conditions

Variation in Transpiration Efficiency and Related Traits in a Groundnut Mapping Population.

Transpiration efficiency (TE) was evaluated in groundnut genotypes JUG 26, ICGS 76, CSMG 84-1, ICGS 44, ICGV 86031, TAG 24 and ICG 2773 using the dry-down method. Pot-grown plants were irrigated to 90% field capacity then subjected to drought stress (i.e. irrigating plants with 70% of the water lost the day before the onset of drought stress) at 28 days after sowing (DAS). Significant variation among the genotypes for TE was evident, with TAG 24 and ICGV 86031 showing the lowest and highest values of TE, respectively. The soil water content where transpiration began to decline relative to the control varied among the genotypes, and these threshold values were negatively correlated to TE. In another dry-down experiment, 318 F8 recombinant inbred lines (RILs) obtained from a cross between ICGV 86031 and TAG 24 were also characterized, along with their parents, for TE. Substantial variation was observed among the RILs for transpiration, TE and specific leaf area (SLA) before and after the imposition of drought stress, and for SPAD chlorophyll meter readings (SCMR) before, during and at the end of drought stress. ICGV 86031 recorded greater TE and SCMA, and lower SLA than TAG 24. The analysis of TE values for the RILs revealed that the trait segregated transgressively and was governed by polygenes. The heritability value was highest for SLA, followed by SCMR. The heritability values were low for TE and transpiration. SLA and SCMR can be useful as alternative indices when the direct biomass-based evaluation of TE is not possible