High Temperature Injury of ripening in rice plant : I. The effects of high temperature Treatments as different stages of panicle development on the ripening

Abstract

A japanica rice (var, Norin-17) was used to test the effects of high temperature treatment (day-night, 35-30°C) from young panicle formation to maturity upon the ripening and the distribution of assimilates, and upon the pollens and anthers. 1) More than 20 per cent sterility occurred when treated just before and after flowering, being progressively decreased as the time of treatment was apart from flowering stage. In general, a larger amount of carbohydrate and nitrogen remained in the straw of the plant which exhibited a higher sterility. The plant with the greatest sterility treated at flowering stage produced grains of the greatest 1000-kernel-weight, being greater than the control. 2) The pollens of plants treated just before and during were smaller in size and stored starch abnormally, often being deficient of inclusions. Besides, the plants had a greater number of anthers which did not open at flowering. These may be related to the high sterility. 3) The plants treated at one or two weeks before flowering produced grains of smaller 1000-kernel-weight, due to smaller grain size especially in its length, although the sterility did not increase by the treatment. In such a plant, more nitrogen and available carbohydrate remained in the straw than the control plant. 4) The grains of plant which was treated under high temperature at several stages during the ripening period decreased in weight, but their sterility did not increase. Grain weight was smallest in the plant treated at 6 to 16 days flowering stage, mainly due to a decrease in grain thickness, and became progressively greater as the time of treatment went away from those period. The sum of TAC(total available carbohydrate)content of panicle and straw was decreased by the high temperature treatment, but more of it remained in the straw of the plants with smaller grains. Nitrogen accumulation did not change significantly by the treatments.