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Comparative study on the fertility and outcrossing characteristics of new dual-purpose genic male-sterile rice in China

ABSTRACT. The widespread application of ‘two-line’ hybrid rice, based on temperature- and photoperiod-sensitive genic male-sterile lines, plays an important role in ensuring global food security. Such lines are fertile in short-day/low-temperature conditions when used for self-breeding, and sterile in long-day/high-temperature conditions when used for hybrid seed production. However, fertility instability and low hybrid seed production of sterile lines are urgent problems. The aim of this study was to increase the stability of pollen sterility by studying the critical sterile-inducing temperature and stigma vitality of 97 newly selected male-sterile lines in China from 2017 to 2020. Sterility gene source analysis showed that 89.7% of the materials contained the tms5 sterile gene. After 6 days of treatment at 23.5°C during the reproductive period, 42 male-sterile lines were sterile. After 10 days of treatment at 23.5°C, the sterility of 12 sterile lines remained stable, indicating a high level of safety for hybrid seed production. After 10 days of low-temperature treatment at 19°C, the fertile pollen rate of 47 of the 97 sterile lines was >70%, indicating a high level of seed reproduction safety. Only six of these 47 male-sterile lines could maintain low fertility after 10 days of treatment at 23.5°C, indicating that they could be used safely for both hybrid seed production and sterile line reproduction. The results of delayed pollination showed that among the six lines, only Zhong 7S had high stigma vitality, and BYXA1S and H10S-2 had medium stigma vitality. Therefore, those three sterile lines have the potential for safe hybrid seed production and high-yield seed reproduction. Based on our research, we propose a new breeding standard of dual-purpose male-sterile lines to promote the development of two-line hybrid rice.