Grain Production and Dry Matter Partition in Rice (Oryza sativa L.) in Response to Water Deficits during the Whole Grain-Filling Period

The grain growth of rice is highly tolerant to water stress throughout the grain-filling period. Despite a large reduction in dry matter production, the grain growth during both the period of active cell division and expansion6), and the subsequent period of rapid starch deposition5) was little affected by water deficits. Reduction in dry matter production due to water stress was almost completely compensated by the increased transfer of reserved assimilates to the grain. But, the plants which experienced drovight during the early stage of grain growth and were relieved from the stress thereafter yielded less than the plants which were well watered throughout the grain-filling period6). Similar response w'as observed in wheat, and a deteriorated root function in stressed plants is suggested as a possible factor for this reduced grain yield9) It is therefore probable that the yield reduction in rice associated with prolonged drought during the period of grain-filling is a result of the indirect effects of water stress through the function of roots with regard to the production of hormonal substances.