Abstract
The length at maturity of various organs and other agronomic characters were measured in 33 mutant lines radiation-induced from a rice variety, Norin 8, which were selected for high fertility and yield. Principal components were extracted from the genetic correlations of organ length. The first component showed an “isometric” phase of variation (general size), in which various organs varied proportionally in length. The second vector showed a variation in the relative length of organs (“allometry”). In this phase of variation, the organs in a stem sequentially increased or decreased in relative length from the top to the base, bringing about the contrast between “upper- elongation” and “lower-elongation” types. In the same manner as in our previous work on F3 lines, the α (“panicle-number” vs. “panicle-length” type, the former having more but smaller panicles and leaves than the latter) and the β (“internode-length” vs. “internode-number” type, the former having fewer but longer internodes and more erect leaves than the latter) variations in plant type were obtained from the mutant lines, when the data for panicle number and mean internode length were adjusted by the score for general size. The α and β plant-type scores were correlated with the scores showing general size and differential relative size of organs, respectively. Possibly, variations in agronomic characters of cereal crops may be largely conditioned by such an isometric and an allometric factor, the former involving the size-number relationship of stems, and the latter representing sequential change in the relative length of organs in a stem.
