Abstract
Although some genetically homozygous rice varieties have two distinct growth types with different leaf numbers (N, N + 1) on the main culm, this phenomenon has not been deeply investigated. In this study, we counted leaf number, recorded heading date, and measured culm length, panicle length, and internode lengths on the main culm in 48 varieties of various origins to detect the universal existence of the two growth types within a population of a rice variety. In all the varieties grown in two cropping seasons, N-leaf plants were headed several days earlier, and had shorter culms and longer panicles of the upper-internode elongation type, than the (N + 1)-leaf plants. However, 12 out of 48 varieties showed high proportions toward a single growth type with more than 0.6 or less than −0.6 in the index of leaf number variation [(No. of (N + 1)-leaf plants −No. of N-leaf plants)/(No. of (N + 1)-leaf plants + No. of N-leaf plants)] in two cropping seasons. Stable high indices were observed in those varieties as Akihikari, Nipponbare, Isehikari, and Hinohikari through four experiments, but other varieties showed unstable indices among the experiments. Differences in the index of leaf-number variation among the rice varieties may be caused by the accumulation of different quantitative trait loci (QTL) which control the leaf number and heading time.
