Effect of timing and severity of water deficit on four diverse rice cultivars III. Phenological development, crop growth and grain yield

Abstract

Water deficit is known to retard phenological development and reduce growth of rice. We investigated whether the ability of a cultivar to extract soil water and to tolerate water deficit affected its growth during and folloing water deficit, and consequently its grain yield. Four contrasting rice (Oryza sativa L.) cultivars (CPIC8, Lemont, Rikuto-Norin 12, and Todoroki-Wase) were subjected to water deficit during either vegetative or reproductive growth stages. We examined the contribution of genotypic differences in water-extraction ability and drought tolerance to phenological development, crop growth rate and grain yield. Biomass production during water deficit was less than 56% of that in irrigated conditions, dependeing on severity of stress and cultivar. Following the relief of water stress, crop growth rate depended on growth stage and severity of stress imposed. The cultivars differed in rate of recovery from water deficit and this was partly attributed to differences in dehydration tolerance. Severe water deficit suspended apical development until rewatering occurred, while mild water deficit reduced the rate of apical development. Water deficit during vegetative growth did not significantly reduce grain yield, whereas water deficit imposed during the reproductive period reduced grain yield to 20-70% of the irrigated control. A small growth rate during panicle development reduced grain number and potential grain size, while cultivars which recovered quickly after water deficit had a relatively larger grain yield. Greater ability to extract water and greater dehydration tolerance during water deficit, increased growth rate during recovery. Selecting for greater water extraction capacity and dehydration tolerance may be useful in improving adaptation of cultivars to water-limited environments.