Genome-Wide Association Study-Based Identification of Loci Controlling Mature Embryo Size in Chinese Wheat Landraces and Their Genetic Effects Analysis

As a critical component of wheat grains, the embryo is closely correlated to nutritional value, germination, and seedling establishment. Mining embryo size loci from genetically diverse Chinese wheat landraces and deciphering their genetic effects will enhance our understanding of the genetic basis of embryo size and provide molecular targets for future breeding programs.

We genotyped 240 Chinese wheat landraces using the 660K SNP array and performed genome-wide association studies (GWAS) via a mixed linear model, integrating embryo size phenotypic data across three environments. Significant loci were subjected to genetic effect analysis and candidate gene prediction.

Phenotypic variation ranges across environments and BLUP values were: embryo length (1.64-3.43 mm), width (0.93-2.58 mm), area (1.10-5.71 mm²), and length-to-width ratio (1.06-2.08), with broad-sense heritabilities of 0.76, 0.47, 0.54, and 0.60, respectively. Significant positive correlations (r=0.271-0.922) existed among embryo traits, and between major embryo traits (length, width, area) and grain length or thousand-kernel weight. A total of 18 stable SNP loci significantly associated with embryo length and area were identified across two environments and BLUP values, which were clustered into four quantitative trait locus (QTL) intervals. These included three QTLs for embryo length and one for embryo area, with colocalization observed between QEA.sicau.3B and QEL.sicau.3B.2. For the major QTL QEL.sicau.1B, we predicted nine candidate genes. Genetic effect analysis revealed that the increasing allele of QEL.sicau.1B significantly enhanced embryo length, grain length and width, thousand-kernel weight, and reduced flowering time, while demonstrating superior effects on seedling root dry weight and shoot biomass, albeit with minor negative impacts on tiller number and spikelet number. Comparative analysis suggested both QEL.sicau.1B and QEL.sicau.3B.2 represent novel loci.

GWAS identified four stable loci significantly associated with embryo size, among which nine potential candidate genes were predicted for the major embryo-length QTL (QEL.sicau.1B). The study demonstrated significant positive correlations between embryo size and grain dimensions, and revealed a functional association with seedling root vigor.