EFFECTS OF THE TIME OF DEEP-WATER TREATME NT ON GROWTH AND LODGING RESISTANCE IN JAPONICA TYPE PADDY RICE (ORYZA-SATIVA L.)

Recently sometimes deep water is used as a growth control technique in rice cultivation in Japan. To make clear the proper treatment for gro wth control, we studied five deep-water treatments (30 cm depth) which were different in start time and period:plot A-1, from productive til ler number determining stage to internode elongation starting stage;pl ot A-2, to heading stage; plot A-3, to ripening stage; plot B, from in ternode elongation starting stage to ripening stage; and plot C, from heading stage to ripening stage. In plots A-I: A-2 and A-3, the percen tage of fruitful culms improved and basal internode diameter increased greatly compared to that of the control ( 5 cm water depth maintained ). However the breaking strength of basal internodes decreased as the treatment period became longer (plots A-2 and A-3). This weakening cou ld be explained by the development of lysigenous aerenchyma and thin c ortical fiber in the internode tissue. In plot B, no improvements were observed in the percentage of fruitful culms and yield components as compared with the control. But remarkable reductions in breaking stren gth and spindly growth were recognized in the basal internodes. The re duction in strength could be explained by the thinness of the cortical fiber and fundamental parenchyma, and a remarkable development of lys igenous aerenchyma. In plot C, little influence of treatment was obser ved on growth habit. These results indicate that treatment which start s from the productive tiller number determining stage to internode elo ngation starting stage has a possibility for rice growth control.