Fine-mapping of , a quantitative trait locus for grain weight in rice ( L.).

Background: Grain 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 and that have been cloned. In the present study, QTLs for grain weight and shape were identified using rice populations that were homozygous at and .

Method: Nine populations derived from the rice cross TQ/IRBB52 were used. An Fpopulation named W1, consisting of 250 families and covering 16 segregating regions, was developed from one residual heterozygote (RH) in the Fgeneration of Teqing/IRBB52. Three near isogenic line (NIL)-F populations, ZH1, ZH2 and ZH3 that comprised 205, 239 and 234 plants, respectively, were derived from three RHs in F. 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-F 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.

Result: A total of 27 QTLs distributed on 12 chromosomes were identified. One QTL cluster, // located in the terminal region of chromosome 2, were selected for further analysis. Two linked QTLs were separated in region Tw31911-RM266. 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. was located in Tw35293-RM266 and affected TGW, GL and GW with the same allelic direction. Finally, was delimited within a 103-kb region flanked by Tw35293 and Tw35395.

Conclusion: with significant effects on TGW, GL and GW was validated and fine-mapped using NIL and NIL-F populations. These results provide a basis for map-based cloning of and utilization of in the breeding of high-yielding rice varieties.