Genetical Studies on Dense and Lax Panicles in Rice : I. Character Expression and Mode of Lax Panicle Rice

Abstract

In order to get information on the genetical mechanism of panicle formation in rice, the character expression of lax panicle rice and its mode of inheritance were inves-tigated. It was observed that the panicle density of rice was dependent not only on the number of spikelets and panicle length, but also on the total number and total length of primary and secondary branches, although their effects on the panicle density varied largely according to the cultivars and strains used in this study. Thus, we recommend the ratio of total spikelets to total length of rachis and primary branches of panicle as the most efiicient method to determine the panicle density in rice at least in so far as the cultivars and strains used in this study are concerned. The spikelet formation of a strain, Soryuto, which has a high laxness, was remarkably responsive to low temperature. When this strain was treated with low temperature at the panicle differentiation stage, various kinds of malformed spikelets were frequently induced. In the extreme cases, no spikelet developed on the panicle branches. In the cross between Soryuto and the dwarf mutant strain induced from a cultivar, Akibare, by X-irradiation, it was found that Soryuto carried a singie recessive gene responsible for the lax: panicle, which was independent of the dwarf gene. The pronounced gene interaction was also observed between the lax panicle gene and the dwarf gene.