Abstract
The outcrossing traits in rice (Oryza sativa L.) affect the yield of hybrid seed production. Using a cytoplasmic male sterile (CMS) line with good outcrossing traits, such as short flag leaf length (FLL), narrow flag leaf width (FLW), wide flag leaf angle (FLA), and elongated panicle neck length (PNL), for hybrid rice seed production, it is possible to avoid the procedure of cutting flag leaves and make the supplementary pollination feasible by machine. In this study, a japonica restorer C-bao as the receptor parent and a primitive japonica accession Ludao as the donor parent were used to construct a chromosome segment substitution line (CSSL) population. The CSSL population was used to detect quantitative trait loci (QTLs) for the four outcrossing traits using a likelihood ratio test based on the stepwise regression (RSTEP-LRT) method. The CSSL population constructed consisted of 163 lines covering 90.7% of the donor genome. Among the seven QTLs detected in the CSSL population, four QTLs were detected in both years. qFLL-4 explained 6.70% of the two-year-averaged phenotypic variance, and the alleles from Ludao decreased FLL 5.1 cm. qFLA-1.1 and qFLA-1.2 explained 7.85% and 21.29% of the 2-year-averaged phenotypic variance respectively, and the alleles from Ludao increased FLA 17.38° and 31.50°. qPNL-8 explained 8.87% of the 2-year-averaged phenotypic variance, and the alleles from Ludao increased PNL 4.44 cm. These favorable alleles identified could be used to improve the outcrossing traits of parents for hybrid rice seed production in rice.
Highlights
Rice (Oryza sativa L. and Oryza glaberrima Steud.) is the leading food crop for over 3 billion people
The highest significant positive correlation was observed between flag leaf angle (FLA) and panicle neck length (PNL) (r = 0.45, p < 0.001 in 2017 and r = 0.54, p < 0.001 in 2018) and the highest significant negative correlation was noticed between PNL and flag leaf width (FLW) (r = −0.36, p < 0.001 in 2017 and r = −0.25, p < 0.001 in 2018). These results indicated that the lines with longer PNL showed larger FLA and narrower FLW, which is beneficial for improving the three outcrossing traits simultaneously, but having longer flag leaf length (FLL), which is not desired to improve the two traits at the same time
In comparison with the results obtained by previous researchers, some QTLs for FLL have been detected on chromosome 4 [6,7,50,51,52,53,54], QTL qFLL-4 linked with RM349 on chromosome 4 detected in our research was a new one, explaining 6.7% of the two-year-averaged phenotypic variance, and the allele from Ludao decreased FLL 5.10 cm if the chromosome region of the locus in restorer C-bao was substituted by Ludao (Table 4)
Summary
Rice (Oryza sativa L. and Oryza glaberrima Steud.) is the leading food crop for over 3 billion people It is grown on 160 million hectares per year in 117 countries with an average production of Agronomy 2020, 10, 28; doi:10.3390/agronomy10010028 www.mdpi.com/journal/agronomy. In the hybrid rice seed production process, farmers need to manually cut one-third to one-half of the flag leaf in the female parent plant at the early heading stage to facilitate cross-pollination. It is a labor-intensive procedure, but professional skills are needed to avoid any damage to young panicles. Using a cytoplasmic male sterile (CMS) lines with good outcrossing traits, such as a short flag leaf length, wide angle, and elongated panicle neck length, can avoid the procedure of cutting flag leaves and make the hybrid rice seed production by machine feasible
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