Dissection and validation of quantitative trait loci (QTLs) conferring grain size and grain weight in rice

Grain size and grain weight contribute greatly to the final grain yield in rice. In order to identify QTLs conferring grain size and grain weight, an F₂ population derived from a cross between two indica rice accessions, Guangzhan 63-4S (GZ63-4S) and Dodda, and its derived F_2:3 population were developed, and were exploited for QTL analysis of the five related traits, namely grain length (GL), grain width (GW), length-to-width ratio (LWR), grain thickness (GT) and thousand-grain weight (TGW). A total of 36 QTLs were detected, and the number of beneficial alleles was contributed roughly equally by the two parents. Among those, 7 QTL regions were repeatedly detected in the two populations. In order to further validate effects of QTLs detected, a BC₁F₂ population derived from a backcross of a mixture of F₂ plants with GZ63-4S was developed and was exploited for QTL selection. Heterozygous regions of 3 QTLs, qGS3, qTGW6.2 and qGT7 were identified respectively, and corresponding near-isogenic lines (NILs) of each QTL were constructed with three rounds of self-crosses. In the background of NILs, qGS3 was responsible for GL, LWR, GT and TGW, qTGW6.2 was for GL and TGW, and qGT7 was for GT and TGW. These results have laid the foundation of further fine mapping work, and could be of great use in breeding and improvement of rice lines with desirable size and yield.