Mapping Of QTLs For Grain Shape And Weight Trains In Rice

Grain shape is the important trait of yield and quality in rice, including grain length, grain width, grain thickness and grain weight and other related indicators. In this study, we perform QTL analysis using an F2population derived from a cross between the japonica variety BL129(wide and thick grain) and the elite indica variety Huazhan (narrow and long grain). Using the linkage map and grain shape, grain weight data of F2populations in Hangzhou for QTL mapping based on analysis with MapDraw, mapmaker3.0and QTLNetwork_v2.1. And a developed near-isogenic line (NIL) HZ, provide a good breeding material for agricultural breeding. We sequenced the GW2gene in BL129and HZ background and compared with the Nipponbare. The specific conclusions were as follows.(1) The parent materials BL129and ZH have extreme differences in grain shape and grain weight. The grain length, grain width, grain thickness and grain weight of BL129were9.55±0.68mm,3.78±0.19mm,2.43±0.10mm and42.35±1.27g respectively. And the grain length, grain width, grain thickness and grain weight of HZ were9.15±0.44mm,2.23?0.15mm,1.71±0.07and16.98±1.03, respectively. All of these traits of the F2population were polymorphic except grain length. We further investigated correlations between grain length, width, thickness and weight in the F2population. Grain width and thickness were positively correlated with grain weight, and grain thickness was positively correlated with grain width. By contrast, the grain length was not correlated with grain width, thickness and weight in this F2population.(2) Selecting116markers from SSR markers, STS markers and InDel markers that have polymorphism between BL129and HZ, and to detect186F2populations for genotype analysis. A genetic linkage map with116markers, covering12chromosomes, was constructed using mapmaker3.0. In the16linkage groups, the average genetic distances were6.4cM-22.5cM, the largest genetic distance was45.9cM, the smallest genetic distance was1.9cM, the average genetic distance was12.4cM and the total distance was1440.7cM.(3) Using BL129/HZ F2grain type and grain weight (including brown rice grain shape data) and genotype data, a total number of10major QTLs are detected on three different chromosomes by QTLNetwork_v2.1software, including qGW2, qGW5, qBRW2, qBRW3, qBRW5, qGT2, qGT5, qBRT2, qTGW2and qTGW5, its contribution rate between11.6%-44.26%. qGW2, qBGW2, qGT2and qBGT2were mapped into an interval between2-4and2-6on chromosome2, suggesting this locus may have pleotropic effects on grain growth. We sequenced the GW2gene in BL129background. Alignment of the nucleotide sequences indicated that BL129had a1-bp deletion in the fourth exon of the GW2gene, compared with the Nipponbare. A CAPS maker developed to detect this deletion, suggesting that GW2is a candidate gene for qGW2and qBGW2, qGT2and qBGT2. qGW5/GW5is a candidate gene for qGW5and qBGW5.(4) We developed a near isogenic line (NIL) named HZ-gw2that contained the gw2allele from the BL129variety in a Huazhan genetic background. HZ-gw2plants exhibited similar growth phenotypes to Huazhan plants. The height of HZ-gw2plants was comparable with that of Huazhan. We further investigated the effects of the gw2allele on grain size. Grains of HZ-gw2were significantly wider, thicker and heavier than those of Huazhan, while the length of HZ-gw2grains was similar to that of Huazhan grains. These results indicate that the gw2allele from BL129can increase grain width, thickness and weight of Huazhan, and must be a good material for molecular breeding.