Abstract
There are two growth types of plants for the number of developed leaves, heading time, and culm and panicle lengths within a population of a homozygous rice cultivar. However, this phenomenon has not been deeply investigated, because of lack of concrete data. Rice breeders and physiologists have paid little attention to it, regarding it as a genetically uncontrollable environmental variation. To study more details of the phenomenon, we grew two near-isogenic lines of rice with each one of the alleles for the Se1 locus conferring photoperiod sensitivity on chromosome 6 under natural long and short day-length conditions. In the line ER homozygous for the earliness allele Se1-e, and the line LR with the lateness allele Se1-u, N-leaf plants headed several days earlier than N+1-leaf plants. The N-leaf plants had shorter culms and longer panicles and were the upper-internode elongation type, whereas the N+1-leaf plants had opposite values of these characters. The proportion of these two kinds of plants changed in lines, plots and experiments. We discuss the meanings of this phenomenon from the viewpoints of rice cultivation to attain the uniform growth of plants, breeding to select individual plants with environmental variation, and fixation test to evaluate the uniformity needed as a cultivar.
