Physiological responses of argentine peanut varieties to water stress. Water uptake and water use efficiency

The water extraction capability and water use efficiency (WUE) of two argentine peanut varieties Florman INTA and Manfredi 393 INTA, respectively classed as drought-sensitive and drought-tolerant were compared. The experiment was grown at two different regimes of water supply. Between 47 and 113 days after sowing (DAS) half of the crop was irrigated, while the other half received no water. Soil water contents, canopy temperature, above ground dry matter and root length density (RLD) were measured periodically during the drought period. Water use (WU), stress degree day (SDD), extraction front velocity (EFV), uptake coefficient, shoot and pod water use efficiency corrected (WUEc) by vapor pressure deficit, and soil resistance were calculated from the measurements. Manfredi 393 INTA had a higher WU than Florman INTA in both irrigated (IRR) and water-stressed (WS) treatments. This was linked to a higher transpiration rate as demonstrated by SDD time course values. The EFV obtained from lineal and logistic fitted models showed a similar pattern for both varieties. However, the logistic function fitted better than the linear model. The observed differences in WU under drought were explained by slightly but consistently higher uptake coefficient values in Manfredi 393 INTA. Uptake coefficient differences between varieties were not associated with RLD; thus, it was not useful as an indicator of the genotypic ability to extract soil water. Florman INTA possessed higher WUEc than Manfredi 393 INTA in both IRR and WS treatments. On the other hand, these differences between varieties were not observed for pod WUEc. Both varieties showed similar values under the irrigated regime because the higher WU on Manfredi 393 INTA was compensated for a higher pod production due to an enhanced partitioning of assimilates to pods. Under WS regime, pod WUEc was significantively reduced in both varieties. The mechanical impedance in the soil upper layer contributed to this reduction. Although critical soil resistance was similar for the two varieties under study. its effect was remarkable on Florman INTA due to a delay in the onset of the beginning pod stage and non-synchronous reproductive development. Manfredi 393 INTA demonstrated an adaptative advantage to drought, expressed in its higher pod production, due to either an earlier onset of beginning peg stage that affected differentially peg penetration into the dry soil upper layer, and an enhanced partitioning of assimilates to pods. (C) 2000 Published by Elsevier Science B.V.