Abstract
This study was undertaken to (I) clarify the gross morphology of the panicle from the view point of growth and differentiation and (II) observe the variation in the panicle structure according to species, strains and genomes in the genus Oryza. In this study 41 strains representing 17 species of wild and cultivated rices were used. Among the characters investigated those concerned with growth were the length of panicle, rachis, internode of rachis, primary branch, and secondary branch, and the diameter of neck node of the panicle, and those concerned writh differentiation were the number of primary branch, nodes in primary branch, secondary branches per primary branch and nodes in secondary branch, and percentage of development of secondary branches. There existed a wide range of an interspecific variation in the panicle structure. In Asian race of O. rufipogon, there had been a reduction in respect of growth and differentiation of panicle of the perennial tyrpe during the course of its evolution to annual type. In terms of growth and differentiation, the panicles of the species representing Angustifoliae were inferior to those of the species representing Oryzae. On cluster analysis the strains could be divided into 5 groups based on the degree of growth and differentiation of the secondary branch in the panicle.
