21. Inheritance of a thermosensitive genic male-sterile mutant of Indica rice
Reena BORKAKATI and S.S. VIRMANI
International Rice Research Institute, P.O. Box 933, Manila, Philippines
Thermosensitive genic male sterility (TGMS) in rice has been reported from China (Sun et al. 1989; Wu et al. 1991; Zhang et al., 1991), Japan (Maruyama et al. 1991) and IRRI (Virmani and Voc 1991). It was reported to be controlled by a single recessive gene in a Japonica rice mutant PL-12 (Murayama et al. 1991). We also studied the inheritance of a TGMS mutant: IR32364 (TGMS) of Indica rice developed at IRRI. This mutant showed complete male sterility at day/night temperature of 32°/24°C but partial fertility at 27°/21°C and 24°/18°C in IRRI phytotron (IRRI 1992; Voc and Virmani, unpublished). We crossed this TGMS mutant with its fertile counterpart IR32364 (normal). Parents (P1 and P2), F1, F2 and backcross (P1//P1/P2) generations were grown together at IRRI farm in the field during 1993 dry season. The materials initiated panicle development during 4 April to 11 April 1993 when the maximum/minimum temperature ranged between 31.0-34.0/21.5-23.6°C. Single plants of these populations were evaluated for pollen (determined by using 1% IKI solution) and spikelet (determined by using two bagged panicles per plants) fertility.
Results (Table 1) showed contrasting differences for pollen and spikelet fertility of the TGMS parent and its fertile counterpart. Pollen and spikelet fertility of most of the plants of IR32364 (normal) ranged between 61-100% although a few plants showed somewhat lesser fertility (41-60%) due to unknown reasons. Pollen and spikelet fertility of the F1 was similar to that of fertile parent indicating that TGMS trait of IR32364 is recessive. The fertile class in F2 and BC generation was therefore considered also to include plants with pollen and spikelet fertility similar to that of P2 and F1 generation plants. Segregation ratios for pollen and spikelet fertility of F2 and BC generation gave a good fit to 3 fertile : 1 sterile and 1 fertile : 1 sterile, respectively indicating thereby that TGMS trait of IR32364 mutant was controlled by a single recessive gene. Studies are in progress to determine allelic relationship between the TGMS gene of PL-12 and that of IR32364.
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