Abstract
The dry weight of each organ including root in topsoil, root density in each soil layer and root morphology of rice plant (Oryza sativa L.) were compared among USA cultivars, semi-dwarf (panicle weight type) Indica cultivars and Japanese cultivars which have different magnitude of tolerance to root lodging, to investigate the eco-physiological basis of root lodging tolerance. Total dry weight of medium grain USA cultivar and Japanese cultivar with similar growth duration were comparable throughout the growing period. Long grain USA cultivar showed less total dry weight than Japanese cultivar. Root dry weight at full heading stage were larger in USA cultivars than Japanese cultivars when compared between groups with the same maturity. The ratio of root to total plant in the dry weight basis at full heading stage was higher in all USA cultivars examined in this experiment than in Japanese cultivars. Larger dry weight of semi-dwarf Indica cultivar resulted in larger root dry weight of root at full heading stage without significant difference in the ratio of root to total weight. Tolerant cultivars to root lodging, including USA and semi-dwarf Indica cultivars, developed more roots in deeper soil layers than susceptible Japanese cultivars.
