UQ eSpace

Abstract

Rice (Oryza sativa L.) is a semiaquatic species which is physiologically, morphologicallyand anatomically adapted to culture in a submerged soil. About 50% of the world’s rice growing area is rainfed and even minor water stress may result in significant yield reduction. Whilst thereis enormous genotypic variation in response to drought and in adaptation to the upland environment, the physiological basis of this variation is not well understood. An examination of variation in physiological and morphological characteristics of several genotypes under a range of stressed and non-stressed conditions was conducted. The contribution of these characteristics todrought resistance and their effect on grain yield was assessed. Field experiments were conducted in three seasons under upland conditions at RedlandBay (27°37’S, 153°19’E) in south-east Queensland to investigate the effect of water stress on growth and yield of rice. Genotypic variation in response to stress was examined in each experiment, with the number of genotypes included ranging between 4 and 40. In each experiment an irrigated upland treatment was included for comparison with various water stress treatments and in one experiment rice was grown under lowland (paddy) conditions to establish the yield potential of several genotypes. In the first three experiments, water stress treatments were rainfedand received periodic rainfall. There were three stress treatments in the first experiment - an early stress, a late stress and a treatment which received both early and late stress separated by a 30-day irrigated period. In the second experiment a 49-day period of severe stress was induced early in growth, while in the third experiment an intermittent, prolonged stress began 37 days after sowing and continued to maturity. It was considered necessary to have greater control overtiming, duration and severity of stress so two further experiments were conducted with the aid of a rain-out shelter. These experiments were more detailed and investigated the effect of a 24-day period of severe stress prior to panicle initiation, and of 30-day mild and severe stress periods during panicle development. The effects of these treatments on phenological and morphological development, dry matter growth and yield, rooting pattern, water use and plant water status were examined. The response to water stress depended on severity, duration and timing of stress.Phenological events (panicle initiation, anthesis and maturity) were delayed by stress in allexperiments. Increased severity and duration of stress resulted in greater reductions in rate ofphenological development while timing of stress determined which phenological events were affected by stress. In the first three experiments all genotypes were sown on the same date and differences in phenology among the genotypes resulted in stress occurring at various stages of phenological development. In the fourth and fifth experiments phenology of genotypes was matched by staggered sowing dates and the effect of stress on rate of panicle development was found to depend on the severity of stress experienced by the crop. Where stress was particularly severe, panicle initiation or panicle development (depending on timing of stress) was suspended inall genotypes until the stress was relieved.