Fertility alteration behaviour of Thermosensitive Genic Male Sterile lines in Rice Oryza sativa L

The utilization of thermosensitive genic male sterility system (TGMS) has great potential for revolutionizing hybrid rice production in tropical countries through simple, less expensive and efficient seed production technology without any limitation in fertility restoration which have been the hindrance for commercial exploitation of heterosis in rice using cytoplasmic genic male sterility system (CMS). However for successful utilization of this novel male sterility system in hybrid rice breeding, knowledge on the fertility behaviour of TGMS lines, critical fertility and sterility temperatures and critical stages of thermosensitivity are highly essential. In this study six TGMS lines viz., TS 6, TS 16, TS 18, TS 29, TS 46 and TS 47 were characterized for their fertility behaviour. The lines were screened for pollen and spikelet fertility by raising the plants at fortnightly interval. All the lines had stable sterile phase with 100 per cent pollen sterility for more than 50 consecutive days during high temperature condition (>30/20oC max/min) and they reverted to fertile with more than 60 per cent pollen and spikelet fertility during low temperature condition (<30/20oC max/min). All the lines except TS 29 showed one distinct sterile phase from March to June, whereas TS 29 had two sterile phases from mid February to mid June and from second week of September to first week of November. Since all the lines were completely sterile for more than 30 consecutive days during sterile phase, hybrid seed production utilising these lines can be taken up by raising the lines in such a way that flowering coincides with sterile phase. All the lines reverted into fertile in two phases. The first fertile phase was short (13-17 days) during July for all the lines except TS 29, for which it was observed during August. The second fertile phase was longer in duration from late November to early February for more than 30 days in all the lines except TS 29, in which it was only for 16 days during December. The maximum pollen and spikelet fertility recorded during this period was 63 to 85 per cent and 58 to 70 per cent, respectively. The correlation analysis between pollen sterility and weather parameters revealed that the daily maximum and mean temperature were the primary factors influencing fertility alteration, whereas sun shine hours, relative humidity and photo period were the secondary factors. The panicle development stages from meiotic division of pollen mother cell (S6) to pollen ripening (S8) were found to be sensitive in TS 16 and TS 29. For TS 18 Stamen and Pistil primordia differentiation to pollen ripening (S4 to S8) were identified as sensitive stages for temperature. The critical temperature inducing fertility alteration in these lines was found to be between 24 and 26oC. These lines satisfied the requirement of stable fertility behaviour for commercial exploitation of these lines in two line hybrid rice breeding.