Mining Candidate Genes and Favorable Haplotypes for Flag Leaf Shape in Rice (<i>Oryza sativa</i> L.) Based on a Genome-Wide Association Study

The shape of the rice flag leaf affects rice yield. Therefore, the detection of quantitative trait loci (QTLs) and alleles related to rice flag leaf shape is of great significance for rice yield improvement. Therefore, in 2019 and 2020, we carried out a genome-wide association study of flag leaf length (FLL), flag leaf width (FLW), flag leaf length–width ratio (FLR), and flag leaf area (FLA), considering 1.3 million single-nucleotide polymorphisms (SNPs) in 173 rice accessions, in order to investigate the effects of various genes on flag leaf shape. An abundance of phenotypic variation was found, with respect to the four flag leaf shape parameters of these accessions. We identified one significant SNP position associated with FLL and FLR on chromosome 5 and one significant SNP position associated with FLW on chromosome 2, which were detected in both of the two years of the study period through general linear model (GLM) and mixed linear model (MLM). Furthermore, three candidate genes—LOC_Os02g56760, LOC_Os05g34380, and LOC_Os05g34600—were found to possibly be significantly related to flag leaf shape in rice. Haplotype analysis indicated that LOC_Os05g34380 is highly associated with flag leaf length and flag leaf length–width ratio, LOC_Os05g34600 is highly associated with flag leaf length, and LOC_Os02g56760 is highly associated with flag leaf width. Our results provide important genetic information for the molecular improvement of rice flag leaf shape, laying the foundation for further cloning and molecular-assisted breeding of flag leaf genes