Abstract
BackgroundPhoto-thermo-sensitive genic male sterile (PTGMS) rice (Oryza sativa L.) is usually considered two-line male sterile rice because of its dual-purpose in two-line hybrid rice system: under short days and low temperatures, it is fertile and used for self-propagation, but under long days and high temperatures, it is sterile and used for hybrid seed production. Therefore, photoperiod and temperature conditions are extremely important for the fertility transition of two-line male sterile rice. In recent years, there have been frequent occurrences of abnormally low-temperature (ALT) resulting in failure of two-line hybrid rice seed production. The daily average temperature (DAT) during ALT events is sometimes higher than the critical sterility-inducing temperature (CSIT) of two-line male sterile rice, of which the night temperature is lower than the CSIT. DAT has been traditionally used as the single indicator of pollen fertility transition, but it is unknown why the fertility of two-line male sterile rice in seed production restored fertility under ALT conditions.ResultsFor Hang93S (H93S), a newly released PTGMS line, we hypothesized fertility transition is determined mainly by the cumulative effective low temperature (ELT) and only a certain duration of low temperature is required every day during the fertility-sensitive period. This study simulated ALTs where the DAT was higher than the CSIT while some segments of night temperature were lower than the CSIT. The results showed H93S exhibited a fertility transition to varying degrees. Moreover, fertility was restored under simulated ALT conditions and pollen fertility increased with increasing cumulative ELT, indicating that the fertility transition was affected primarily by the cumulative ELT. Results also indicated that pollen fertility increased as the number of treatment days increased.ConclusionsThe fertility transition is caused mainly by the cumulative ELT. In two-line male sterile rice breeding, the effects of day length, ALT at night, and continuous response days should be considered together. The present study provides new insight into fertility transition so breeders can more effectively utilize the two-line male sterile rice, H93S, in breeding programs.
Highlights
IntroductionThe fertility of two-line male sterile rice can be restored under low temperatures and short day length, resulting in self-propagation, while high temperatures with long days maintain male sterility and can be used for hybrid seed production (Ding et al 2012; Zhou et al 2012; Chang et al 2016; Wang and Deng 2018)
At TΔ2, the treatment corresponded to ΣTΔ2 = 4.08 °C·d and a daily average temperature (DAT) of 24.29 °C. These results indicated that the DATs of the two temperature treatments were higher than the critical sterility-inducing temperature (CSIT) of H93S (23.0 °C), owing to the effective low temperature (ELT) treatment at night, the fertility of H93S restored, as reflected by pollen fertility percentage (PFP) of 3.10% and 1.53% and corresponding Seed Setting Percentage (SSP) of 1.31% and 1.01%, respectively
The main cause of fertility transition is not the DAT being lower than the CSIT but instead is the effect of cumulative ELT
Summary
The fertility of two-line male sterile rice can be restored under low temperatures and short day length, resulting in self-propagation, while high temperatures with long days maintain male sterility and can be used for hybrid seed production (Ding et al 2012; Zhou et al 2012; Chang et al 2016; Wang and Deng 2018). Owing to this unique fertility transition relationship, specialized breeding procedures are required, including the use of artificial climate chambers, the proper timing of planting, and the selection of suitable locations (DeGuzman and Oard 2019).
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