Varietal differences in growth, lodging and related characters of rice plants broadcasted in submerged paddy field at different densities

Seeds of rice cultivars, Nipponbare, Takanari and Chugoku 153 were broadcasted in the submerged paddy field at different densities. The density of seedlings after establishment was in the range of about 60 to 240 plants m(-2) for Nipponbare and Chugoku 153, and about 40 to 130 plants m(-2) for Takanari. Serious lodging occurred in Nipponbare at the ripening stage due to bending at the base of the stem, and the degree of lodging tended to be larger in the Stand With a higher density. The lodging vas slight in Chugoku 153 and Takanari. A close correlation was observed between the degree of lodging and the reduction in grain yield. In the direct-sown plants without serious lodging, the grain yield vas comparable to or even larger than the conventionally transplanted plants. The flexural rigidity of the stem at basal internode, which affects the lodging due to the stem bending. vas larger in Chugoku 153 and Takanari, The larger flexural rigidity vas caused by both of culm and leaf sheath in Chugoku 153 and mainly by culm in Takanari. In Nipponbare. the flexural rigidity of the stem vas the smallest due to the smaller flexural rigidity of the culm with smaller moment of inertia of area. The larger culm flexural rigidity resulted from the larger Young's modulus in the stand with louver density and smaller degree of lodging in Nipponbare, These results indicate that a larger moment of inertia of area and Young's modulus are important characters for increasing the flexural rigidity of the culm.