Physiological responses of argentine peanut varieties to water stress.: Light interception, radiation use efficiency and partitioning of assimilates

Abstract

In Argentina, peanut production is concentrated in areas where unpredictable and intermittent periods of water deficit occur almost every year especially, during the pod growth period. Florman INTA is the most popular variety among peanut producers, but it is highly sensitive to drought. Manfredi 393 INTA was released as a drought-tolerant variety. Differences between these varieties in radiation interception and crop mass accumulation relative to light levels, as well as in allocation of assimilate to economic yield under water deficit, have not been previously studied. An experiment was set with two different regimes of water supply. Half of the crop was irrigated (IRR) from sowing to maturity, while the other half received no water between 47 and 113 days after sowing. The fraction of PAR intercepted, ( f), leaf area, pod and vegetative above-ground biomass and leaf carbon dioxide exchange rate (CER) were measured periodically during the water deficit period. The leaf area index, degree of leaf folding, canopy extinction coefficient, radiation use efficiency (RUE), partitioning factor, ( p), and harvest index (HI) were calculated from the measurements. Under water stress, f was reduced in both varieties with respect to their controls, and the reduction was proportionally higher in Florman INTA as a consequence of a higher leaf area reduction and degree of leaf folding. However, f remained higher in Florman INTA than in Manfredi 393 INTA due to the enhanced capacity of the former to generate leaf area under non-limiting water supply. RUE values were higher in Manfredi 393 INTA than in Florman INTA, both under irrigation as well as under severe water deficit, where they were obtained using a two-parameter exponential model. The reason for the higher RUE values in Manfredi 393 INTA was its ability to maintain a higher leaf CER. Partitioning to pods under irrigation was greater in Manfredi 393 INTA than in Florman INTA, as a result of a longer pod filling period and higher p. Towards the end of podfill, there was a rapid increase of p in Florman INTA, but too late to improve its HI. Under water stress, the time course of p for both varieties was lower than in the IRR treatments and consequently, HI at harvest was reduced. Low HI values could be attributed to some extent to the mechanical impedance of the upper soil layer, caused by water deficit. Mechanical impedance alters the relation among p and HI values obtained under irrigation and water stress. However, even if it is accounted for, cultivars with high HI under IRR conditions usually have high HI under water deficit.