Stay-Green Trait Assessment using the Leaf Incubation Method to Examine the Maintenance of Assimilation Rates under High Temperature Conditions during the Grain-Filling Period in Rice

AbstractRice yield and quality decrease under high temperature conditions during the grain-filling period particularly in early-ripening cultivars that are directly subjected to midsummer heat. As the grain growth rate increases under high temperature conditions, the grain requires greater amounts of assimilates for the shortened grain-filling period and occasionally experiences a lack of assimilates. The stay-green trait that can maintain assimilation during the active grain-filling period is expected to mitigate the negative impact on grains due to the lack of assimilates. Our objectives were to evaluate the stay-green trait of rice maintaining assimilation rates under high temperature conditions during the active grain-filling period using the leaf incubation method. When whole leaves or leaf segments were floated on water at 20 – 40oC under dark conditions, a leaf color reading (SPAD) showed steady genotypic differences at 25 – 35oC. When flag leaf segments of early-ripening cultivars from the Japanes...