VARIETAL DIFFERENCE OF THE CELL-WALL COMP ONENTS AFFECTING THE BENDING STRESS OF THE CULM IN RELATION TO THE LODGING RESISTANCE IN PADDY RICE

We investigated which cell wall components of the culm affect the bend ing stress of the culm using seven rice cultivars. A small difference in the cell wall composition was noticed among the cultivars. The rela tionship between this composition and the varietal difference of the b ending stress was not found. In order to clarify the relationship betw een the quantity of the culm materials and the bending stress, the den sities of the cell wall materials (the cell wall contents of the culm per volume of the culm tissue) were compared among cultivars. There wa s a large varietal difference in the densities of glucose, xylose and lignin. In Tainung 67 and Taichung 189 with a large bending stress, th e densities of glucose, xylose and lignin were higher than those in Ko shihikari and Fujiminori with a small bending stress. On the other han d, in Milyang 23 with a large section modulus and a small bending stre ss, the densities of glucose and xylose were as large as those in Tain ung 67 and Taichung 189, and the density of lipin in Milyang 23 was as small as those in Koshihikari and Fujiminori. Furthermore, the partia l correlation coefficients were calculated among the bending stress, t he density of lignin and the density of cell wall monosaccarides. The results showed that density of lignin of the culm was significantly co rrelated with the bending stress (r=0.81) in the seven cultivars. The results of this study indicate that the density of lignin is the main factor responsible for the varietal difference in the bending stress w hich is related to the lodging resistance in paddy rice.