Conversion of a rice CMS maintainer into a photo- or thermo-sensitive genetic male sterile line

Yanning Tan,Zhizhong Sun,Xiabing Sheng,Yongfei Zhang,Weiping Wang,Meijuan Duan,Dong Yu,Xuewu Sun,Xiaolin Yin,Baohua Fang,Ling Liu,Dingyang Yuan

doi:10.1007/s11032-018-0805-2

Abstract

A maintainer line of 3-line hybrid rice commonly presents a certain genetic distance to a 2-line restorer line, but in many cases, 2-line restorer lines present defects upon recovery of the object cytoplasmic male sterile (CMS) line of the maintainer line, which impedes the utilization of their heterosis. Here, we report a strategy and an example of converting a maintainer into a photoperiod/temperature-sensitive genic male sterile (P/TGMS) line with an almost identical genetic background, thus maximizing the heterosis. Firstly, through treatment of maintainer line T98B with 60CO-γ irradiation, we identified the TGMS line T98S, which is sterile at higher temperatures and fertile at lower temperatures. Secondly, the T98S line was proven to be identical to T98B with regard to genetic background via an examination of 48 parental polymorphous SSR markers and exhibited excellent blossom traits similar to those of T98B, with an extensive forenoon flowering rate of 75.92% and a high exertion rate of 64.59%. Thirdly, in a combination test, three out of six hybrids from T98S crossed with 2-line restorer lines showed a yield increase of 6.70–15.69% for 2 consecutive years. These results demonstrated that the strategy can generate a new P/TGMS line with strong general combining ability (converted from a maintainer line), thus helping to increase the genetic diversity of male sterile heterotic groups.

Highlights

It is of great importance to breed high-yield hybrid rice to feed the growing worldwide population
In the production of F1 hybrids, the male sterility conferred by the cytoplasmic male sterile (CMS) line is restored by a so-called restorer line (R line), as male sterility is controlled by cytoplasm and nucleus interaction, with the nuclear R gene being dominant over the cytoplasmic CMS gene (Yuan et al 2003)
In another exploration of heterosis between CMS lines and 2-line restorer lines, we investigated the yield factors from combinations of T98A crossed with 2-line early-season restorer lines such as Xiang-Zao 45 (XZ45), Z116, and Z996 and found that the combinations presented a panicle and grain structure better than that of the commonly used hybrid rice Zhu-Liang-You 819 (ZLY819) (Table S2; Fig. 4)

Summary

Introduction

It is of great importance to breed high-yield hybrid rice to feed the growing worldwide population. The 3-line and 2-line systems are the two basic methods employed to generate hybrid rice seeds. These two methods differ in breeding efficiency due to their use of two different types of male sterile lines. The 3-line system utilizes a cytoplasmic male sterile (CMS) line, whose multiplication is managed by using a maintainer line. In the production of F1 hybrids, the male sterility conferred by the CMS line is restored by a so-called restorer line (R line), as male sterility is controlled by cytoplasm and nucleus interaction, with the nuclear R gene being dominant over the cytoplasmic CMS gene (Yuan et al 2003). Less than 5% of current germplasm resources can be used as restorer lines for 3-line system hybrid production, which makes it difficult to obtain elite combinations (Yuan 1997; Huang et al 2014)

Methods

Results

Discussion

Conclusion