CHANGES IN PHYSICAL AND CHEMICAL CHARACTE RISTICS OF CULM ASSOCIATED WITH LODGING RESISTANCE IN PADDY RICE UNDER DIFFERENT GROWTH-CONDITIONS AND VARIETAL DIFFERENCE OF THEIR CHANGES

The present investigation was undertaken to examine which physical and chemical characteristics of the culm associated with lodging resistan ce changed under different growth conditions using three varieties. Th ree different conditions were prepared: (1) ''Border'' (Border of the rice population was made by reaping several rows in the south side at the maximum tiller number stage, and rice plants were grown under stro ng light intensity and low humidity compared with ''Control''.), (2) ' 'Shade'' (50% Shade of the population was treated from the maximum til ler number stage to heading time) and (3) ''Control'' (Untreated rice population). Change in the degree of lodging and the lodging index was largely dependent on variation in the breaking strength of the basal internode. The breaking strength was much larger in ''Border'' and muc h smaller in ''Shade'' than that in ''Control'' for all varieties. The degree of change in the breaking strength was more pronounced in Kosh ihikari which has a small breaking strength, however, the change was s maller in Taichung 189 or Milyang 23 which have large breaking strengt h. With the exception of ''Shade'' in Milyang 23 with a large section modulus, these changes in the breaking strength were not due to the se ction modulus but rather to the bending stress. The density of glucose , xylose and lignin were correlated with the bending stress in each va riety, and their correlations were the closest on Taichung 189. The de gree of the increase in bending stress accompanied by a concomitant in crease in the densities of xylose and lignin was much larger in Taichu ng 189 and Koshihikari than in Milyang 23, and the efficiency of the i ncrease in bending stress to the increase in density of lignin was the highest in Taichung 189.