| Percentage of grains with chalkiness (PGWC) is one of the most important of rice appearance quality. Grain chalkiness is not only associated with poor rice appearance quality, but also with high levels of damage to the kernel during milling and reduction of eating and cooking quality. High PGWC has become a major reason of low rice quality of rice varieties in our country, especially for hybrid rice.1000-grain weight (TGW), is mainly determined by synthesis and accumulation of starch and the size of kernel, is an important factor of yield components. Improvement of TGW contributes to increase grain yield. But improvement of TGW is usually gone with increasing of PGWC. In this study, a backcross inbred lines (BIL) population and a chromosome segment substhitute lines (CSSL) population derived from the cross of Koshihikari (japonica) and Kasalath (indica) were used to detect QTL and epistatic effects and genotype X environment (GE) interaction for PGWC and TGW, and CSSL carried overlapping chromosome segments of Kasalath in a genetic background of Koshihikari. A recombinant inbred lines (RIL) population derived from the cross of Koshihikari (japonica) and Guichao2 (indica) were used to detect QTL and epistatic effects and GE interaction for PGWC. A set of CSSL created using 9311 as the recurrent and PA64S as the donor was used to map QTL for PGWC. A main- effect and stable QTL for PGWC was fine mapped by using secondary F2 populations derived from a cross between the target CSSL and the recurrent parent. Difference of yield components and physicochemical characteristic of starch between C-51 and 9311 were investigated. The results thus obtained should be useful for the simultaneous improvement of TGW and PGWC and map- based cloning of target QTL. The main conclusions are as follows:1 Seven QTL and two pairs of epistatic interactions were identified using Koshihikari/Kasalath CSSL population in 2005-2007. Three QTL and three pairs of epistatic interactions for PGWC were identified using BIL population in 2005 and 2006, and all of QTL had a GE interaction. Four QTL and six pairs of epistatic interactions for PGWC were identified using RIL population in 2004-2006, of them, three QTL had a GE interaction.After comparative analysis of map, a total of eleven QTL for PGWC was detected using three populations. Of them, qPGWC-3, qPGWC-6a, qPGWC-8, qPGWC-10b and qPGWC-12 had been reported in previous studies. While six QTL for PGWC had not been reported and could be new QTL. A total of eleven pairs of epistatic interaction for PGWC were detected but none was repeatedly detected in different populations. Three loci, including the locus located in the interval between S13849 and R2635 on chromosome 1, qPGWC-6a and qPGWC-10b, interacted with other loci in two populations. There were QTL participating in the epistatic interactions in the three populations, indicating that QTL not only affected PGWC by its additive effects but also had an influence on PGWC by interacting with other loci. The epistatic interactions detected in CSSL population belonged to interaction between two loci from one chromosome while two different chromosomes in BIL and RIL populations. These results offered available gene resources and information for molecular breeding of PGWC, and revealed that genetic network of PGWC is complicated.2 Six QTL and three pairs of epistatic interactions for TGW were identified using Koshihikari/Kasalath CSSL population in 2005-2007. Of them, two QTL were detected in three years and one QTL were detected in two years; all of epistatic interactions were detected in two years. Seven QTL and eleven pairs of epistatic interactions for TGW were identified using BIL population in 2005 and 2006. Of them, four QTL had a GE interaction; six pairs of epistatic interactions had a GE interaction.After comparative analysis of map, a total of eleven QTL for TGW was identified using two populations, of them, two QTL were repeatedly detected in two populations, i.e., qTGW-6c and qTGW-7b; and seven QTL, such as qTGW-2a, qTGW-2b, qTGW-3b, qTGW-3c, qTGW-6b, qTGW-7a and qTGW-7b, were reported in previous studies, and four new QTL were identified in this study.A total of fourteen epistatic interactions for TGW were identified but none was repeatedly detected in different populations. Two loci, including qPGWC-6b and qPGWC-7b, interacted with other loci in the two populations. There were QTL participating in the epistatic interactions in the two populations, of them, qTGW-6b and qTGW-7b were repeatedly identified in the two populations and the alleles from Koshihikari decreased TGW in the former while increased TGW in the latter, and they interacted with each other and other loci, indicating that QTL not only affected TGW by its additive effects but also had an influence on TGW by interacting with other loci. All of the epistatic interactions detected in CSSL population belonged to interaction between two loci on one chromosome while two different chromosomes in BIL population. The discovery of different types of epistatic interactions and one locus interacting with multiple loci implied that genetic network of TGW is complicated.There was a significant positive correlation (P<0.001) between TGW and PGWC in the CSSL and BIL populations and in the three years. Two QTL (qPGWC-6 and qTGW-6a, qPGWC-7and qTGW-7b) simultaneously controlling PGWC and TGW were detected in two populations, and the allele from Koshihikari simultaneously decreased PGWC and TGW in the locus (qPGWC-6 and qTGW-6a). Seven QTL only controlled PGWC or TGW, of them, one QTL controlled PGWC while other six QTL (qTGW-2b, qTGW-3b, qTGW-3c, qTGW-6b, qTGW-7a, qTGW-10a and qTGW-10b) controlled TGW. There were some QTL reported for PGWC or TGW near to the other QTL. The different breeding strategies were adopted according to the directions of allele effects from parents in breeding program.3 Two QTL for PGWC were identified using PA64S/9311 CSSL population. qPGWC-6 is closely linked to Wx, and qPGWC-7 has a PVE (%, phenotypic variance explained) of 28.18%. Lines C-51, C-52 and C-62 harboring qPGWC-7 were all associated with a significantly (P<0.001) higher PGWC than 9311 in at least two of the three environments, and the difference ranged from 54.3% to 78.9%, indicating the effects of the qPGWC-7 were stable across three environments. Based on secondary F2 populations derived from the cross of C-51 and 9311, the QTL qPGWC-7 was dissected into a single gene. Then, the qPGWC-7 was further mapped between InDel 14 and InDel 3 on chromosome 7, with a 44kb region of BAC clone, using the 8073 C-51/9311 F2 plants and SSR and InDel markers developed in our laboratory.4 TGW of C-51 was 4.55% higher than that of 9311 (P<0.05), while other yield components showed no significant difference. Protein content of C-51 was much lower than that of 9311, while the slightly difference of amylose content and fat content between C-51 and 9311 were observed. The degree of crystallinity of C-51 was 46% lower than that of 9311(P<0.001). Significant difference was observed the amylopectin chain-length distribution of C-51 and 9311, especially for long chains, while short chains showed no significant difference. These results showed that TGW, protein content, amylopectin chain-length distribution and degree of crystallinity could be associated with the formation of grain chalkiness. |
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