Expression of thermosensitive genic male sterility in rice under varying temperature situations

Response of thermosensitive genic male sterility in rice to varying tempera ture situations was studied by using four TGMS lines. In three sets of maxi mum, minimum and their combined temperatures, it was observed that maximum temperature played a predominant role in influencing sterility/fertility of TGMS lines under the combined regimes. Expression of a TGMS gene was found to be influenced by the genetic background of the recipient lines. Exposur e for more than 8 hours of 32 degreesC was found necessary to induce comple te male sterility in indica TGMS lines: IR68945-4-33-4-14 and IR68949-11-5- 31 while, more than 4 hours of such exposure was enough to induce sterility in case of their japonica donor Norin PL 12. Sudden interruption with 27 d egreesC even for 2 hours under the sterility inducing regime of 32/24 degre esC could induce partial fertility in the line IR68945-4-33-4-14. However, the line ID 24 remained completely sterile even with 10 hours of interrupti on with 27 degreesC. An interruption with lower temperature of 27 degreesC for 4 hours for even one day induced partial fertility in IR68945-4-33-4-14 . The period of four to eight days after panicle initiation was the stage m ost sensitive to temperature variations. Hybrid rice breeders need to devel op numerous genetically diverse TGMS lines, which possess critical sterilit y inducing temperature of 28 degreesC and are not affected by sudden interr uptions with a lower temperature for few hours daily for a couple of days.