Improvement Of Quality Traits Of Elite Maintainer II-32B In Hybrid Rice Using Molecular Marker-assisted Selection

Developing rice varieties with good quality have become an important object of rice breeding program and the breeders need to meed the demands of the consumers for high-quality rice grains, as the people’s living standard are improved. In this study,II-32 B, an elite maintainer with high combining ability, high adaptability and poor appearance, cooking and eating quality, was used as the recipient parent and crossed with Chuan106 B, a new maintainer line characterized as having high appearance, cooking and eating quality and other good agrinomic traits. The genes GS3, q SS7, Wx and Os2-AP of Chuan106 B were introduced into II-32 B to improve its yield and quality by backcrossing procedures combining with marker-assisted selection and phenotype screening. The main results are as follows:1. Twenty-one BC2F5 improved lines of II-32 B which carry different target alleles of grain quality were obtained by marker-assisted selection backcrossing and phenotype screening. Those lines introduced the genes GS3 or q SS7 increase 1.77 mm of the average grain length and 1.00 of the ratio of grain length to width as compared to II-32 B.2. Different allelic combination of GW8, GS3, and q SS7 results in grain weight variation in the improved lines. The alleles for wide grain type at GW8 combined with the long grain alleles either from GS3 or q SS7 can increase grain weight significantly.3. Sixteen lines of these 21 have lower chalky grains compared to II-32 B. However, these16 lines do not all carry the low chalky alleles of Chalk5, indicating that there are other genes causing the difference in chalky grains between II-32 B and Chuan106 B besides the gene Chalk5.4. The lines carrying Wx and alk of Chuan106 B have high cooking and eating quality compared to II-32 B, in which the amylose content is decreased to 12 %-16.7 % due to the Wx gene introduced from Chuan106 B.5. Three improved lines(205040, 205045, 205058) have significantly higher yield than II-32 B in the field plot testing, and increased the yield by more than 7 %. These results suggest that the related genes or chromosomal segments from Chuan106 B could improve the grain quality and yield of II-32 B.6. Based on the polymorphism SSR markers and SNP microarray, the genotyping results indicate that most of improved lines are homozygous after two times backcrosses and four times self-crossing. The background recovery rates of most selected lines range from80 % to 92 %, and their heterozygosity are less than 5 %.7. After comprehensive evaluation of the grain quality, yield and the other agronomic traits of the improved lines, five lines(205004, 205040, 205042, 205045, 205058) were selected to direct application in rice breeding due to their promising attributes. Among them, 205040, 205045, 205058 with low amylose content and soft texture which meet the preference of consumers in China and Southeast Asia; 205004, 205042 with high amylose content can be use in South Asia and South America. All these lines can be used to develop new sterile lines to improve the quality and yield of hybrid rice.