CONDITIONS INDUCING FERTILITY ALTERATION AND ECOLOGICAL ADAPTATION OFPHOTOPERIOD-SENSITIVE GENIC MALE-STERILE RICE

The pollen fertility of photo-sensitive genic male-sterile (PGMS) line s is regulated interactively by photoperiod and temperature. There is a temperature range within which the pollen fertility alteration of PG MS is regulated by photoperiod, being sterile at long days and fertile at short days. The critical values of day length and temperature vary as the PGMS gene(s) is (are) transferred into different genic backgro unds. According to the temperature reactions in response to fertility alterations, the current sterile lines fall into four photothermal typ es. The climatic adaptation of these is different. Lines of the high-l ow (a high critical fertile temperature with a low critical sterile te mperature point) group have both stable sterile and fertile periods in the low-altitude subtropical rice-growing areas, which are the major rice-production areas df the world. We could exploit them in hybrid ri ce production there by a two-line method, because there is no need for both male-sterile and maintainer lines. At high altitudes of the subt ropical and tropical rice-growing areas, lines of this group are unsta ble in their sterility. The low-low group is stable in sterility in lo ng-day conditions at all temperatures, and at high temperatures despit e day length. They could be used for hybrid seed production from the t ropical through to temperate rice-growing conditions. However, their p ollen fertility, and hence, seed multiplication, is easily lost in sho rt days if high temperatures occur. The high-high group of sterile lin es can be conveniently multiplied in short days, but their sterility i s not stable in long days if temperature decreases in the critical fer tility alteration period. The low-high group is stable at higher tempe rature irrespective of photoperiod, and this could be used in the trop ics, but their sterilities are not stable in long days if lower temper atures are encountered. Their multiplication in short-day conditions m ay also be affected by high temperature.