Abstract
In the previous paper, it was clarified that the decrease in dry matter and grain productions under deficient soil moisture conditions differed between cultivars classified into the same ecotype, and it was suggested that root system development might be responsible for the varietal differences. To investigate causal factors of the differences in dry matter production and yield between the cultivars, ecophysiological characters and root system development were compared between the populations of Enrei and Tachinagaha in the field. The net assimilation rate was high in Tachinagaha compared with Enrei because of the high leaf xylem water potential and low leaf diffusive resistance during the daytime, and the less decrease in the photosynthetic rate with senescence. This resulted in high dry matter production and high grain yield in Tachinagaha. Root length density measured by the core sampling method and root length measured by the minirhizotron method were both larger, especially in the deep soil layers, in Tachinagaha. The amount of soil water depletion was also larger, especially at the deep soil layers in Tachinagaha, probably due to greater water absorption by the plants. These results indicated that the root system was well developed in the deep soil layers in Tachinagaha compared with Enrei as soil moisture was depleted. The root system development might be responsible for the differences in the ecophysiological characters between Enrei and Tachinagaha.
