Studies on the growth habit of rice varieties : 1. Influence of tiller limiting upon the growth

1. Two varieties, Taihei-mochi as a variety of "many-panicle" and Toyokuni as that of "heavy-panicle" type were subjected to an experiment, in which later tillers of plants other than the limited number of stems, ie. 1, 5, 10 or 15 including main stem, were cut off as soon as they appeared, and the plants were compared with those left free. 2. Compensation effect of tiller limiting was most remarkably observed in increase of average panicle weight, the increase being mainly caused by increased average number of grains. Number of panicle branches, panicle length, and proportion of fertile grains to the total number of grains increased in this order. Increases were the cases also in number of nodes and length of main culm. 3. The conspicuous increase of the number of grains on single panicle as an effect of tiller limiting is due largely to intensified density of glume setting. 4. With regard to the compensational effects, ear growth and enrichment predominate over stem elongation; and elongation of uppermost internode does over that of the other part of the stem. 5. Another phase of compensation effects was acceleration in development of main-stem leaves, elongation of plant hight and heading time. Promotion of the ear growth and enrichment, at that time, predominates also over acceleration of the growth of other vegetative organs. 6. The grades of increase or acceleration by tiller limiting were larger in Taihei- mochi than in Toyokuni as to number of main-culm nodes, heading time, main-culm length and perdentage fertile grains. Acceleration of stem elongation became markedly to decline towards heading time, and the declination was more distinctive in Toyokuni than in Taihei-mochi. In number of panicle branches, somewhat larger grade of increase was recognized in Toyokuni, while no appreciable difference was shown between the two varieties as to increased grades in panicle length, single-panicle weight and number of grains of single panicle. Possible mechanisms of these phenomena were discussed.