Spikelet Sterility and Flowering Response of Rice to Water Stress at Anthesis

Abstract

Water deficits at the anthesis stage of rice (Oryza sativa L.) induce a high percentage of spikelet sterility and reduce grain yield. This study attempted to elucidate the direct effects of water stress on panicle exsertion, spikelet opening, and spikelet desiccation leading to spikelet sterility. A well-watered treatment and two water stress levels were imposed in pot-grown plants of IRAT 13 (upland cultivar) and IR20 (lowland cultivar) at the time of flowering under greenhouse conditions A cultivar difference was observed in the flowering response to water stress with a high sensitivity in IR20. The time course of panicle exsertion showed an inhibitory effect due to the low panicle water status. Low panicle water potentials significantly reduced the number of opened spikelets. Spikelet opening was completely inhibited at panicle water potentials below −1·8 MPa and −2·3 MPa in IR20 and IRAT 13, respectively. However, the peak spikelet opening time in a day was not influenced by the stress treatment. Spikelets in stressed panicles were observed to remain open for a longer period than in the well-watered panicles. The role of turgor in spikelet opening is also discussed in the study. At low panicle water potentials, severe desiccation of spikelets and anthers was noted. The deleterious effects of water deficits on spikelet opening and spikelet water loss contributed to reduced spikelet fertility