ECOPHYSIOLOGICAL STUDY OF ROOT LODGING TOLERANCE IN DIRECT-SEEDED RICE CULTIVARS

To investigate the morphological and physiological characteristics rel ating to root lodging tolerance in direct-seeded rice plant, anchoring ability, root growth and its distribution to soil layers were compare d among root lodging-susceptible Japanese varieties, tolerant USA vari eties and Korean semi-dwarf indica varieties. Pushing resistance, i.e, the maximum resistance of plant to horizontal pushing and inclination of shoot to 45 degrees toward the vertical direction, was higher in t olerant USA varieties and Korean semi-dwarf indica varieties than in s usceptible Japanese varieties. Tolerant varieties developed a larger a mount of roots at full heading stage than susceptible Japanese varieti es, due to the higher rate of dry matter allocated to roots in USA var ieties and higher crop growth rate in Korean semi-dwarf indica varieti es. Also, tolerant varieties developed a larger amount of roots in dee per soil layers than susceptible varieties. The pushing resistance was remarkably reduced when root elongation to the subsoil layers was pre vented by laying an unwoven cloth between the topsoil and subsoil laye rs. The higher soil strength and bulk density in the subsoil layers wa s attributed to the higher efficiency of a unit root weight in the sub soil layers for anchoring compared with that in the topsoil layers. Th e above results indicate that root growth, especially root development in the subsoil layers, contributes significantly to the anchoring abi lity and lodging tolerance in direct-seeded rice plant.