Development Of Rice Near-isogenic Lines And Discovery Of New Genes Of Grain Shape

The grain quality of hybrid rice has not been content with people's life in our country, and need to improve immediately. The discovery of valuable genes of the grain quality from various rice germplasm is becoming imperative. Shanyou63 is a hybrid with large growth area in China, and Zhenshan97B (ZS97) is the maintainer line of Zhenshan97A, the mother of Shanyou63. Using ZS97 as recurrent parent and more than one hundred and eighty varieties origined from different countries and areas as donor parents, we have developed a lot of advanced backcross lines with the similar genetic background of ZS97 through intensive backcrossing and self-crossing. One hundred and ninety-six advanced backcross lines (ABL) were chosen because of their grain shapes changed distinctly from that of ZS97B, and were derived from nine donor parents. Referring to public molecular linkage map of rice, 124 SSR markers, which evenly distributed on the rice genome, were selected for genotyping of the ABLs. The objectives of our study are to construct a set of near-isogenic introgression lines with altered grain shapes and then to discover newly valuable quality genes using the near-isogenic introgression lines (NIIL). The main results of the study are as follows:1. Most of 196 ABLs have the similar performances in plant height and heading data, whereas the grain shape changed distinctly different from the recurrent parent ZS97B. The results indicate these ABLs have the same background with ZS97B except that only one or few chromosomal segments derived from the donors affect grain shape.2. The polymorphism among 10 parents (ZS97B and 9 donors) was analyzed by using 124 SSR markers. The genetic variations were detected between at least one donor parents and ZS97B, and the polymorphism percentages range from 23.3% to 64.4% with an average of 43.4%. The gene diversity index also shows large genetic differences among the 10 parents.3. These ABLs derived from nine donor parents (KDML105, IR65482-4, 93-11, Nipponbare, JIANGXISIMIAO, UP15, MARSHI, BASMATI385, GAYABYEO) are classed as nine groups. The restorage percentage of ZS97B background of nine group NILs: 95.8%, 88.1%, 96.1%, 89.4%, 98.5%, 97.2%, 97.4%, 97.4%, 95.9 %, with an average of 95.1%. This is consistent with the theoretical value of the background restorage in BC3 generation. Obviously those ABLs derived from two donors IR65482-4 and Nipponbare have lower background restorage percentages.4. Graphical genotyping strongly indicate the genomic background of nine grouped ABLs is highly similar to the ZS97B except few small introgression segments in the ABLs. The average number of the introgressed chromosomal segments over all ABLs is 5.5 and the average length is 13.5cM. Those ABLs with the similar genetic background of ZS97 are thus considered as the near-isogenic introgression lines (NIILs).5. Fourteen quantitative trait loci (QTLs) of grain shapes were detectedby %2 test. These QTLs were mapped on eight different chromosomes in rice and their locations can also be read on the graphical genotypes.6. A series of allelic genes (or different small introgression segments) were detected oneach of the 14 QTLs using the NIILs. For instances, five alleles were detected on marker locus (RM111) on chromosome 6 and locus RM224 on chromosome 11 respectively. Four alleles also showed on the other seven QTLs, which located nearby the marker RM572, RM562 and RM486 respectively on chromosomel, RM241 on chromosome 4, RM215, RM245 on chromosome9, and RM17 on chromosome 12, respectively. In addition, three alleles on locus RM7 on chromosome 3, RM574 on chromosome 5 and RM481 on chromosome 7, two alleles on locus RM520 and RM514 both on chromosome 5 were also identified.7. Of these fourteen QTLs, three grain shape QTLs that located respectively nearby the marker RM562 on chromosomel, RM7 on chromosome3 and RM574 on chromosome5 are highly consistent with the results in various studies reported previously, however, the other eleven QTLs are newly identified in our study, and are useful for improvement of the grain quality.