THE EFFECT OF HIGH-TEMPERATURE ON THE ACCUMULATION OF DRY-MATTER, CARBON AND NITROGEN IN THE KERNEL OF RICE

Transferring rice plants (Oryza sativa L. cv. Calrose) growing at 27/22-degrees-C to a range of day/night temperatures 7 days after heading resulted in little variation in kernel size with temperature in the range from 24/19-degrees-C (mean 21.7-degrees-C) to 30/25-degrees-C (mean 26.7-degrees-C). This is close to the mean monthly temperature recorded for the rice growing areas of southern Australia during the period of kernel development. There was a significant drop in kernel dry weight with a further increase in temperature to 33/28-degrees-C and 39/24-degrees-C. When plants were transferred to a temperature of 36/31-degrees-C for periods of 8 days, commencing at regular intervals from heading, the greatest change in dry weight of the kernels occurred when the treatment commenced 12 days after heading and the kernels were in the linear phase of dry matter accumulation. The flow of nitrogen into kernels was more stable than that of carbon as temperatures were increased, with little change in nitrogen (mg) per kernel until the temperature was greater than 33/28-degrees-C. Changes in temperature away from the optimum (27/22-degrees-C) always resulted in an increase in the concentration of kernel nitrogen. The greatest reduction in kernel nitrogen (mg kernel-1), like that of carbon, occurred in high temperature treatments commencing 12 days after heading.