Abstract
In order to breed highly palatable cultivars suitable for direct sowing in rice, we tried to incorporate the genes for low-temperature-germinability into highly palatable Japanese cultivars and selected excellent backcrossed lines with low-temperature-germinability. First, we examined ten Japanese cultivars and ten foreign cultivars for their low-temperature-germinability (the proportion of the germination rate at 15°C to that at 25°C after 7 days of incubation) and found that most of the foreign cultivars which were directly sown in their own countries were extremely useful as donors of low-temperature-germinability. Secondly, we developed five backcrossed BC2F2 populations (Koshihikari 3/M202, Hinohikari 3/M202, Koshihikari 3/Italica Livorno, Koshihikari 3/Mutashali and Kinuhikari 3/Mutashali) and selected them for low-temperature-germinability. From all populations, we obtained the lines superior to each recurrent parents. In particular, from Koshihikari 3/M202 (66 lines), Hinohikari 3/M202 (51 lines) and Koshihikari 3/Mutashali (51 lines), we obtained eight, eleven and one line, respectively, which showed excellent (over 81%) low-temperature-germinability. Then we picked out these excellent lines (Hinohikari 3/M202) as donors of futher back-crossing. Finally, we developed backcrossed BC3F2 lines (Hinohikari 4/M202, 35lines) and selected five excellent lines with high low-temperature-germinability. In conclusion, it would be possible to breed highly palatable cultivars suitable for direct sowing by introducing low-temperature-germinability derived from foreign cultivars such as M202 into good eating-quality cultivars.
