| Peanut (Arachis hypogaea L.) genotypes Pearl Early Runner (PER), PI 383426 (PI), Early Bunch (EB), and Florunner (FLR) were grown in field plots and in greenhouse tubes to study their response to drought.;In the greenhouse, length of taproot and node progression were recorded on plants grown in soil in clear acrylic tubes. Leaf area, root density, dry weight of leaves, stems, and roots were measured at 61 days of age.;In the field the genotypes differed in the extraction of water at deeper depths. Pearl Early Runner extracted less water at deeper layers and therefore wilted and closed its stomata sooner.;Plants of PER in the stressed plots had higher values of SDR and lower values for all water potential components throughout the drying cycle.;Two irrigation treatments were imposed in the field experiment: optimum irrigation throughout the crop cycle, and optimum irrigation except during 59 to 88 days after planting. Measurements were taken for: stomatal diffusive resistance (SDR), leaf water potential components, leaf area expansion, rooting density versus depth, soil water status, and yield.;Leaf area expansion and growth of the cotyledonary branch were reduced by drought for all genotypes but PER was affected the most.;Root density of PER was also reduced most by drought especially at the deeper depths. This genotype had the largest yield reduction in response to water stress.;In the greenhouse experiment, the genotypes differed in the rate of taproot elongation and in the rate of node development on the main stem. There were differences in root weight and density at various depths, but PER had the lowest values, especially below 60 cm. The root to shoot ratio was highest for EB and lowest for PER.;The results suggest that the wilt susceptible PER allocates more photosynthate to shoot growth but less to root growth, especially at deeper depths. Since stomatal response to internal water status in PER was not different from other genotypes, its earlier wilting, lower turgor, reduced growth, and stomatal closure under drought conditions appear to be caused by differences in root growth and extraction of water from the soil. |
