2020 Volume 89 Issue 2 Pages 172-178
Rapid generation advancement for rice breeding is actively undertaken at the Tropical Agriculture Research Front, Japan International Research Center for Agricultural Sciences in Ishigaki Island, in the southernmost part of Japan. Rice populations are grown there twice or thrice a year in order to shorten the breeding time. Twenty-nine Japanese rice varieties originating from the northern region of Hokkaido to the southern region of Kyushu were cultivated in the paddy fields. Although all varieties showed normal fertility at first cropping (sown on 4th March), most of the varieties from the west of the Kanto region showed more than 10% sterility during second cropping (sown on 15th July) and late cropping (sown on 28th August). In particular, some varieties from the Kyushu region, viz.,“Shinrei,”“Nishihomare,”and “Saiwaimochi,” showed nearly 60% sterility during late cropping. The temperature during these cropping seasons was neither too high nor too low to induce sterility. With delayed cropping, days to heading became shorter, particularly in strongly photo-sensitive varieties from the west of the Kanto region. Sterility was thought to be related to the shortening of heading time under short-day conditions.
