Inheritance of panicle types classified by the nodal distribution pattern of secondary spikelets in rice (Oryza sativa L.).

Abstract

The inheritance of rice (Oryza sativa L.) panicle types classlfied by the nodal distri-bution pattern of the number of spikelets on the secondary rachis branches was investigated using four varieties belonbaing to different ecospecies. Reimei (a modern cultivar from Japan, japonica) and Stirpe 136 Anthocyane (a large grain variety from Italy) had a large number of spikelets on their secondary rachis branches at the lower rachis nodes and an extremely small number at the upper rachls nodes. Mao-zu-tao (an old cultivar from China, indica) had a large number of spikelets on its secondary rachls branches at the upper rachis nodes ancl a small number at the lower rachis nodes. Panbila (a modern cultivar from U.S. A, , inclica) had a large number of spikelets on the secondary rachis branches at both the lower and upper rachis nodes. The number of spikelets on the primary rachis branch of each rachis node was about 6.0 and showed little change In the parents, t.he F1 and F2 generations, indicating the existence of genetical similarity among the parents. In the Mao-zu-tao x Reimei cross, the number of spikelets on the secondary rachis branches at the upper rachis nodes was controlled by four independent dominant genes (Ssp-1, Ssp-2, Ssp-3 and Ssp-4) and that at the lower rachis nodes by a suppressor gene (Su-1). The Su-1 gene was closely linked with Ssp-3 and controlled by Ssp-1, Ssp-2 and Ssp-3. In the Panbila x Stirpe 136 Anthocyane cross, the mode of inheritance of the n.odal distribution pattern of the number of spikelets on the secondary rachis branches ¥vas very s'imi]ar to that of the Mao-zu-tao x Reimei cross. However, in this case, three inclependent clominant genes (Ssp-1. Ssp-2 and Ssp-3) controllecl the number of spikelets on the secondary rachis branches at the upper rachis nodes. A suppressor (Su-2) and a activator (Act) genes, which were closely linked with the Ssp-1 and Ssp-3 genes, respectively, controlled the number of spikelets on the secondary rachis branches at the lower rachis nodes. The Su-1. Su-2 and Act genes were considered to be the regulator genes. It was estimated that they would be stimulated by the Ssp genes and control the structural genes which would express the initiation and barowth of the secondary spikelets at the lower rachis nodes.