15. 
Genetic differences among Japanese varieties in relation to Fl hybrid sterility 
in the crosses with a Nepalese variety, Gamadi
M. 
MAEKAWA, T. RIKIIsHI, T. MATSUIJRA and K. NODA
Research Institute for Bioresources, Okayama University, Kurashiki, 710-0046 Japan

 
A Nepalese rice variety, Gamadi (1-106), whose non-exserted panicles protect grains from the damage by the rice bug Leptocorisa varicornis, has high protein content of more

 
than 14% in the brown rice (Shrestha et a!. 1981). Gamadi is important as a genetic resource for breeding of rice with higher protein content. However, Maekawa (1993) observed extremely high sterilities of pollen and spikelets in F! hybrid between 1-106 and Yukihikari (Hokkaido variety in Japan). From the result of the reciprocal cross, the high hybrid sterility between 1-106 and Yukihikari was found to be controlled by nuclear genes. Maekawa (1993) also reported that Fl hybrid of I-106x Taichung 65 (T-65) showed semi-sterility of pollen, resulting in 13% of spikelet fertility. These results suggest that Yukihikari carries different genes for hybrid sterility from T-65 or an additional gene to the sterility gene(s) possessed by T-65. Furthermore, from these results it is presumed that there are genetic differences in Fl hybrid sterility genes of the crosses with 1-106 among Japanese varieties. Thus, in order to determine the origin of genes for extremely high sterility in F! hybrid of 1-106 x Yukihikari, spikelet and pollen fertilities in Fl hybrids between 1-106 and 37 ancestors of Yukihikari and 2 ancestors of T-65 were examined in 1997. Out of 37 ancestors of Yukihikari, varieties bred in Hokkaido district in Japan except for Tomoemasari showed extremely high sterilities of both spikelets and pollen in Fl hybrids of the crosses with 1-106 (Fig. 1). Akage (not shown in Fig. 1), which made rice cultivation possible in Hokkaido and is origin of Bozu, also showed extremely high sterilities in Fl hybrid of its cross with 1-106. High spikelet sterilities observed in Fl hybrids of the crosses between Hokkaido varieties and 1-106 were considered to be caused by high pollen sterility. Out of 20 cross combinations between Hokkaido varieties and I-

 
 
106, Fl hybrid of the cross between Tomoemasari and 1-106 only showed semi-steriuities of spikelets and pollen. On the other hand, most of varieties bred in other districts except Hokkaido in Japan showed semi-steri!ities of spikelets and pollen in Fl hybrids of the crosses with 1-106. A Chinese variety, Reishiko, which was the gene source of Pi-k, was found to show the same degree of sterilities in Fl hybrid as Hokkaido varieties. The genes for semi-fertility in Fl hybrid of the cross between T-65 and 1-106 was presumed to be derived from Shinriki. These results suggest that hybrid sterility genes which Hokkaido varieties carry might be linked with some adaptive characters for northern part of Japan. Semi-sterility of pollen in Fl hybrid of the cross between T-65 and 1-106 is found to be controlled by a single gene acting gametophytically (data not shown). However, the causal genes for extremely high sterility in Fl hybrids of the crosses between Hokkaido varieties including Yukihikari and 1-106 still remain unclear.
References
Maekawa, M., 1993. Hybrid sterility between 1-106, Indica and Japonica rices. Jap. J. Breed. 43 (Suppl.2):
303.
Shrestha, G.L., M.H. Heu and S.Z. Park, 1981. Effect of daylength on the panicle exsertion of panicle enclosing “Gamdi” rice cultivar. Korean J. Crop Sci. 26: 121-124.