1973 Volume 42 Issue 2 Pages 214-219
A japanica rice (var, Norin-17) and two indica rice (var, IR-8 and Boshito) were used to test the effects of temperature treatment separately given to the panicle and the straw including roots upon the ripening and the distribution of assimilates to the both parts. The plots of treatments are indicated as follows: 35/35, 30/35, 35/30, 30/30, 25/25, 20/25, 25/20, 20/20 in 1969 and 35/35, 25/35, 35/25, 25/25°C in 1970. The numerator indicates day-air-temperature around the panicle, and the denominator around the straw, respectively. The night-temperature is 5°C lower than the respective day-temperature. 1) In the three varieties, 1000-kernel-weight was markedly decreased by high panicle temperature (35°C), but increased by near optimum panicle temperature (20-25°C). Lowering of temperature around the straw was also effective, but not so significant in improving 1000-kernel-weight. The kernels ripened under high panicle temperature became inferior in quality with least normal, but much opaque, chalky, and milky-white kernels. 2) Sol.-N/Prot.-N ratio in the straw was increased when both panicle and straw or straw only were treated at high temperature. The total sugar concentrations and total-surgar/ crude-starch ratios in both panicle and straw were also increased by treating the panicle or straw or both by high temperature, suggesting some physiological abnormality occurred in the plant. 3) The amount of TAC (total available carbohydrate) stored per tiller was greatest at 25/25, being followed in order by 35/25, 25/35, 35/35. Relatively more TAC was translocated and stored in the panicle with the less amount remained in the straw, when the panicle was treated with lower temperature. On the contrary, the total nitrogen accumulation per tiller was greater under higher temperature, greatest at 35/35, being followed by 25/35, 35/25, 25/25 in order. However, when the temperature around panicle was lowered relatively more nitrogen accumulated in the panicle, resulting in less nitrogen in the straw. The high nitrogen accumulation under high temperature was partly caused by new tillers with new roots emerged from higher nodes after about two weeks of treatment. 4) The leading factor which decreased 1000-kernel-weight under high air-temperature was considered to be an early cease of the receiving function of panicle of assimilates from the straw, although the temperature around straw was also effective in changing 1000O-kernel-weight.