Effects of short period treatments at low temperature (9 degree Centigrade) on growth of rice [Oryza sativa] plants at the tillering stage

The rice plants cv. Sasanishiki (3 plants/pot) were moved into the controlled growth chamber at 9 degrees C when half of the leaf blade (LB) of the seventh leaf (L7) was emerged (H plot) or when the whole seventh leaf blade (LB7) was fully emerged (W plot). The plants were kept at that temperature for 1, 2, 4, and 8 days. Plant did not grow during the treatment and began to continue the growth after treatment. In the 8-day treatment plots (H8 and W8 plots) plants sustained heavy damage and at 1 or 2 weeks after the treatment about 30% of plants had died. The effects of the treatments on the leaf length or on the tillering behaviour are as follows. 1) The length of LB and the leaf sheath (LS) treated at rapid elongating stage (LB7, LS7, LB8 of H plots and LS7, LB8 of W plots) were shorter than that of untreated plants, but on the other hand the length of LB or LS treated just before the rapid elongating stage (LS8, LB9 of H plots and LS8, LB9, LS9, LB10 of W plots) were longer than that of untreated plants. Tiller growth of the treated plants was slower than that of untreated plants. The percentage of emerged tillers at expected nodes after treatment was smaller than that of untreated plants. The percentage of emerged tillers and the tiller growth rate indicated the rate of the damage that plants sustained. In this study, there were no reason to say that a tiller bud was sensitive to low temperature in the specific developmental stage