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

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 ⁶⁰C_O-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.

Keywords: 60CO-γ irradiation; Heterosis utilization; Hybrid rice; Maintainer line; Photoperiod/temperature-sensitive male sterile line.

Fig. 1

T98S showed a P/TGMS trait in-field and in-chamber. Fertility observations on May 6th (a), July 12th (b), and September 25th (c) in the field, and fertility performance under 22.0 °C/12.0 h (d), 28.0 °C/12.0 h (e), 22.0 °C/13.5 h (f), and 28.0 °C/13.5 h (g) in-chamber

Fig. 2

Detection of the genetic backgrounds of T98S and T98B using 48 parental polymorphous SSR markers. T98S and T98S presented indistinguishable genotypes for each polymorphous SSR marker. Each marker was used to test two samples, with the first being T98B and the second being T98S. M, 50 bp DNA ladder

Fig. 3

Comparison of flowering habit traits among T98S, T98A, and T98B. Asterisk (*) indicates a significant difference at p < 0.05

Fig. 4

Evaluation of combinations via a main yield factor. The combination test of T98S and T98A crossed with the same group of restorer lines. (a) Seed-setting rate. (b) Grain numbers per plant. (c) Actual yield per plant. All combinations with T98S show a normal SSR and AYP, while the combinations with T98A were defective in these aspects, but grain number per plant is less likely affected when comparing T98S and T98A. Single and double asterisks indicate p < 0.05 and p < 0.01, respectively