Evaluation of genetic resource for cultivar and genus differences in grain filling capacity under high temperature conditions in rice and wheat

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Objectives of the project were to clear responses of the grain filling to higher temperature and know mechanisms of the grain filling reduction, and evaluate the cultivar and genus differences to seek genetic resource for high temperature resistant cultivars in rice and wheat. Temperature and tropical zone rice cultivars were grown in paddy filed and suffered from two different higher temperatures than ambient condition in ventilated air plastic covered houses of different length. Fertility response to high temperature differed between cultivars but the relationship between temperature and grain filling rate of two cultivars was similar. Sowing time for spring wheat was changed from early to late times in the field of Perth, Australia and the plants suffered from different temperature during the grain filling period. Under higher temperature conditions grain filling period shortened and yield reduced. The grain number decreased after anthesis and thus the potential yield changed. However a response of the grain filling among different sowing plants was similar. When ear in rice and wheat was cultivated in solution culture system under different temperatures, the most highest rate of grain filling was around 30℃ in rice and 15℃ in wheat. Sucrose synthase activity decreased and ct-amylase activity increased with an increase of temperature in wheat and when assimilate supply during the grain filling period by thinning treatments increased some enzyme activity increased. Our results suggest that grain filling response to high temperature in rice and wheat is similar although temperature range for the optimum growth differed and assimilate supply affects grain filling activity. Cultivar difference in grain filling under higher temperature conditions seems to be small in rice and wheat. Further research should be continued to overcome the impact of high temperature on the grain filling under the future climate change.