Abstract
BackgroundGrain weight is a grain yield component, which is an integrated index of grain length, width and thickness. They are controlled by a large number of quantitative trait loci (QTLs). Besides major QTLs, minor QTLs play an essential role. In our previous studies, QTL analysis for grain length and width was performed using a recombinant inbred line population derived from rice cross TQ/IRBB lines. Two major QTLs were detected, which were located in proximity to GS3 and GW5 that have been cloned. In the present study, QTLs for grain weight and shape were identified using rice populations that were homozygous at GS3 and GW5.MethodNine populations derived from the indica rice cross TQ/IRBB52 were used. An F10:11population named W1, consisting of 250 families and covering 16 segregating regions, was developed from one residual heterozygote (RH) in the F7generation of Teqing/IRBB52. Three near isogenic line (NIL)-F2 populations, ZH1, ZH2 and ZH3 that comprised 205, 239 and 234 plants, respectively, were derived from three RHs in F10:11. They segregated the target QTL region in an isogenic background. Two NIL populations, HY2 and HY3, were respectively produced from homozygous progeny of the ZH2 and ZH3 populations. Three other NIL-F2 populations, Z1, Z2 and Z3, were established using three RHs having smaller heterozygous segments. QTL analysis for 1000-grain weight (TGW), grain length (GL), grain width (GW), and length/width ratio (LWR) was conducted using QTL IciMapping and SAS procedure with GLM model.ResultA total of 27 QTLs distributed on 12 chromosomes were identified. One QTL cluster, qTGW2/qGL2/qGW2 located in the terminal region of chromosome 2, were selected for further analysis. Two linked QTLs were separated in region Tw31911−RM266. qGL2 was located in Tw31911−Tw32437 and mainly controlled GL and GW. The effects were larger on GL than on GW and the allelic directions were opposite. qTGW2 was located in Tw35293−RM266 and affected TGW, GL and GW with the same allelic direction. Finally, qTGW2 was delimited within a 103-kb region flanked by Tw35293 and Tw35395.ConclusionqTGW2 with significant effects on TGW, GL and GW was validated and fine-mapped using NIL and NIL-F2 populations. These results provide a basis for map-based cloning of qTGW2 and utilization of qTGW2 in the breeding of high-yielding rice varieties.
Highlights
Rice is one of the staple food crops and consumed by half of the world’s population
Grain weight is a key component of grain yield in rice, which is mainly determined by grain length, width and thickness
The Tw35293−RM266 region had R2 of 14.50% for TGW and 18.60% for grain length (GL), which were much higher than the R2 values for these two traits detected in the other three regions
Summary
Rice is one of the staple food crops and consumed by half of the world’s population. Enhancing grain yield is always among main objectives of breeding programs. Grain weight is a key component of grain yield in rice, which is mainly determined by grain length, width and thickness All these traits are quantitatively inherited and controlled by both major and minor genes. The remaining two genes, GL7 /GW7, and GS9, have similar influences on grain length and width with opposite allelic directions, they hardly affect grain weight (Wang et al, 2015b; Wang et al, 2015c; Zhao et al, 2018) Identification of these genes have facilitated the breeding of high-yield rice varieties. QTGW2 with significant effects on TGW, GL and GW was validated and fine-mapped using NIL and NIL-F2 populations These results provide a basis for mapbased cloning of qTGW2 and utilization of qTGW2 in the breeding of high-yielding rice varieties
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