Dryland Rice Response to an Irrigation Gradient at Flowering Stage1

Abstract Sensitivity of rice ( Oryza sativa L.) to flowering stage water stress is well recognized. However, as with other cereals, there is lack of field research which quantifies plant and soil water status at the flowering stage in relation to water stress‐mediated reductions in crop yield. A rice cultivar was subjected to six levels of irrigation using a line‐source sprinkler system in the field on a silty clay loam, Typic Hapludoll soil during the dry season in which a stable rainless period is the climatic norm. Irrigation level 6 (wettest) was irrigated at the rate of 1.10 of pan evaporation while level 1 (driest) relied solely on pre‐line source water storage. Evapotranspiration during the 15‐day treatment period at flowering was linearly related to grain yield. The dominant yield component influencing grain yield was spikelet sterility. At irrigation level 6 in which soil moisture was reduced to 95% of the total crop extractable water, midday leaf water potential was −0.9 MPa, and spikelet sterility was 20%. At level 1, soil moisture was 28.6% of the total crop extractable water, midday leaf water potential −2.5 MPa, and spikelet sterility 73%. The exsertion of the rice panicle was found to be sensitive to changes in leaf water potential. Up to 30% of water stress‐mediated spikelet sterility was associated with poor panicle exsertion. The degree of panicle exsertion during flowering stage water stress may be a useful visual criterion in the selection of breeding lines with high degree of reproductive stage drought resistance.