ANALYSIS OF GENETIC VARIATIONS IN PLANTT TYPE OF RICE

IV. GENERAL GROWTH RATE, OSCILLATING GROWTH AND ALLOMETRIC PATTERN

Abstract

Between-line variations in the final size, the time at which half of the final size was attained (t_1/2), and the growth rate at t_1/2, were studied for the panicle and first to fourth (from the top) internodes. Materials used were 23 mutant lines radiation-induced from a rice variety, Norin 8, which were selected for high fertility and yield. For each of the above three values, principal components were extracted from correlations between the five organs, and the “genetic vectors” showing genetic contributions of the components to the respective organs were computed. In the final size, as reported in our previous paper, two latent phases of genetic variation were distinguished, one showing the general size (isometry), and the other showing an allometric pattern that brought about the variation between “upper-elongation” and “lower-elongation” types. Variations in the growth rate of organs similarly comprised an isometric and an allometric phase. Lines with a generally high growth rate had a large general size at maturity. In the allometric phase, lines whose panicle and third internode elongated relatively slowly had a relatively high growth rate for the first and second internodes. Such lines tended to be the “upper-elongation” types at maturity. As the panicle and third internode elongate some days before the elongation of first and second internodes that results in heading, the allometric pattern of growth rate suggests that the lines vary in the rhythm of development. This was proved by an observation of the change of relative growth rate in the period from panicle elongation to heading. It was suggested that genes modify the rhythm of development and bring about the size variations observed at maturity.