QTL-Seq Identified a Major QTL for Grain Length and Weight in Rice Using Near Isogenic F2 Population

Mapping and isolation of quantitative trait loci (QTLs) or genes controlling grain size or weight is very important to uncover the molecular mechanisms of seed development and crop breeding. To identify the QTLs controlling grain size and weight, we developed a near isogenic line F-2 (NIL-F-2) population, which was derived from a residual heterozygous plant in an F-7 generation of recombinant inbred line (RIL). With the completion of more than 30x whole genome re-sequencing of the parents, two DNA bulks for large and small grains, a total of 58.94 Gb clean nucleotide data were generated. A total of 455 262 single nucleotide polymorphisms (SNPs) between the parents were identified to perform bulked QTL-seq. A candidate genomic region containing SNPs strongly associated with grain length and weight was identified from 15 to 20 Mb on chromosome 5. We designated the major QTL in the candidate region as qTGW5.3. Then, qTGW5.3 was further validated with PCR-based conventional QTL mapping method through developing simple sequence repeat and Insertion/Deletion markers in the F-2 population. Furthermore, recombinants and the progeny tests delimited the candidate region of qTGW5.3 to 1.13 Mb, flanked by HX5009 (15.15 Mb) and HX5003 (16.28 Mb). A set of NILs, selected from the F-2 population, was developed to evaluate the genetic effect of qTGW5.3. Significant QTL effects were detected on grain length, grain width and 1000-grain weight of H12-29 allele with 1.14 mm, -0.11 mm and 3.11 g, which explained 99.64%, 95.51% and 97.32% of the phenotypic variations, respectively.