Relation between the Modification of the First Bract to the Flag Leaf and the Number of Shoot Units without Crown Roots in the Rice Plant

Abstract

Previously, the author clarified that in rice cultivars in Hokkaido and having ten to twelve or so leaves on the main stem, the number of shoot units without crown roots frequently happened to vary among the main stems which had the same number of leaves on them8). So, the causal factor was investigated with reference to the modification of the first bract to the flag leaf, for it was made clear that the rice plant of which first bract had been modified to the flag leaf showed the characteristic feature of the internode elongation9). The number of shoot units without crown roots was apt to be more in the rice plant of which first bract had been modified (Tables 1 and 4, where the number of shoot units without crown roots is expressed by the position of the top shoot unit with crown roots, for the shoot units upper than this is the ones without crown roots). This tendency was superior in the rice plant having twelve or thirteen leaves on the main stem than that with eleven leaves (Table 1). Increase in the number of shoot units without crown roots in the rice plant with the modified flag leaf was attributed to the change of the internode elongation, especially to the elongation of the fourth one (Fig. 1). The frequency of the modification of the first bract to the flag leaf was about sixty to seventy percent in these rice plants and it was markedly higher than in cultivars having more leaves (Tables 2, 3 and 5). Some discussions were made on why the modification of the first bract to the flag leaf happened so frequently in these rice plants.