Fujian Agricultural College, Fuzhou, China
A number of male-sterile mutants were found in an early-maturing Indica strain,
5460, which was derived from IR54, in the autumn of 1986. There was no
discernible difference between the mutants and their mother strain except for
pollen fertility. One of the mutants, named 5460A, was chosen as the parent of
crosses. The F\1\ (5460A/5460) was normal in pollen fertility under both 16-
hour and 10-hour daylengths when tested in the phytotron of the Shanghai
Institute of Plant Physiology (SIPP) in the winter of 1986.
When grown at Fuzhou (26.05degrees N) in 1987, 30 B\1\F\1\ plants (5460A/5460//5460) and the check (5460) was fully fertile. But fertility transformation was observed in many of the F\2\ plants (5460A/5460). Partly sterile F\2\ plants became completely sterile in mid July. When these plants were cut back at the end of July, they produced new tillers which flowered in early September. Then, all the B\1\F\1\ plants were fertile and sterile F\2\ plants became gradually fertile by mid September.
When tested at the SIPP in the winter of 1987, each plant was divided into two parts, one grown under 16-hour day length and the other under 10-hour day length. All the plants under 10-hour days were fertile, but a part of B\1\F\2\ and F\3\ plants under 16-hour days showed male sterility. Our data suggest that this male sterility is controlled by a recessive gene whose action is expressed under a long day.
The original strain 5460 has good agronomic characters, resistance to diseases and insects, and a high rate of stigma exsertion which promotes outcrossing. This should enable us to employ the material for breeding of so-called "two- line hybrid rice", in so far as a stable male-sterile line is established.
We have now obtained a stable photoperiod-sensitive male-sterile line. It's male sterility is expressed under the long day in mid July, and the male- sterile plants can be pollinated by a suitable variety to produce F\1\ seed. When the plants are cut back at the end of July, they produce new tillers which are fully fertile under natural shortdays in mid September, and set their own seed. This line can serve as both male-sterile line and maintainer.