ECOPHYSIOLOGICAL CHARACTERISTICS RELATED WITH LODGING TOLERANCE OF RICE IN DIRECT SOWING CULTIVATION .1. COMPARISON OF THE ROOT LODGING TOLERANCE AMONG CULTIVARS BY THE MEASUREMENT OF PUSHING RESISTANCE

The objective of this series is to investigate the relationships between root lodging tolerance and root characteristics of rice (Oryza sativa L.). In this paper, the pushing resistance was measured in different cultivating conditions and among cultivars including Japanese and USA varieties by the method developed by Uemura et al., to evaluate the contribution of anchorage ability of each rice cultivar to the root lodging tolerance. High negative correlation was found between pushing resistance and root lodging degree of each cultivar examined. Sowing depth and water management affects the pushing resistance, but the effect of sowing density in a row on the pushing resistance was not dear. Varietal difference in pushing resistance was larger compared with the variation of pushing resistance with the change of cultivating condition mentioned above. Improved cultivars of USA and semidwarf (and long ear) Indica cultivars used in this experiment showed higher pushing resistance than Japanese cultivars examined. The higher variation of pushing resistance among cultivars than that by culture practices indicates that the breeding of cultivars with higher root lodging tolerance could be a possible way to improve lodging tolerance of direct sowing rice.