Inheritance of male sterility in the Oryza sativa Taichung 65 like cytoplasmic substitution lines derived from O. rufipogon K61 strain

Motomura, K.; Higa, Y.; Murayama, S.; Ishimine, Y.

Japanese Journal of Tropical Agriculture 36(1): 8-13


ISSN/ISBN: 0021-5260
Accession: 002412133

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Lines RT61A and RT61B were isolated by recurrent backcrossing, in which Oryza rufipogon line K61 was used as the initial female parent and O. sativa cv. Taichung 65 as the recurrent pollen parent. The phenotypes of lines RT61A and RT61B were identical to that of Taichung 65 except that line RT61A had 50% sterile pollen (semisterile) and RT61B represented complete pollen and seed fertilities. In order to elucidate the genetic mechanism of this sterility and its restoration, an investigation was conducted by crossing Taichung 65 with RT61A and RT61B. When RT61B was crossed with Taichung 65, all the offspring showed complete pollen and seed sterilities, indicating that this line has male sterile cytoplasm and no fertility restoration gene and that Taichung 65 also does not have this gene. When RT61A was crossed with paternal Taichung 65, the resulting F1 segregated into semisterile pollen and normal seed fertile individuals, and complete pollen sterile and seed sterile individuals at a ratio of approximately one to one. This phenomenon coincided with a segregation pattern from monoallelic genes and can be explained as follows. RT61A had male sterile cytoplasm and a pair of fertility restoration genes in the heterozygous state. In the next generation, when this line was crossed with Taichung 65 (having recessive genes for restoration fertility), heterozygous individuals were produced with semisterile pollen and normal seed fertility. In addition, homozygous individuals for recessive genes were also produced with complete pollen and seed sterility. When the heterozygous individuals were self-pollinated, they all produced normal fertile plants in the F2 but their pollen fertility was normal in half of the individuals and semisterile in the other half. There were no completely male sterile plants. Such a mode of inheritance is gametophytic, i.e., pollen grains having the dominant restoration gene were normally developed, while recessive pollen grains degenerated during pollen development. On the other hand, all F1 and F2 individuals obtained by crossing Taichung 65 as a maternal parent with paternal RT61A showed normal seed and pollen fertilities, thus indicating the possibility that cytoplasm of Taichung 65 will offer normally developed pollen grains with both dominant and recessive genes. Such a possibility was confirmed because, when 18 F2 individuals were selected at random and crossed with the sterile line, these individuals were found to consist of three groups as follows: 7 F2 individuals which yielded all progeny of normal seed fertility and pollen semisterility without segregation, 6 F2 individuals which yielded seed and pollen sterile plants and normal seed fertile and pollen semi-sterile plants at a ratio of one to one, and 5 F2 individuals which yielded progeny with sterile seed and pollen only. From these results, it was concluded that male sterility and its restoration in these lines was induced by interaction between the cytoplasm and a single locus for fertility restoration, and that the mode of restoration was gametophytic.