|AOUN, MERIEM - Washington State University|
|CARTER, ARRON - Washington State University|
Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2021
Publication Date: 7/14/2021
Citation: Aoun, M., Carter, A.H., Morris, C.F. 2021. Genome-wide association mapping of the ‘super soft’ kernel texture in white winter wheat. Theoretical and Applied Genetics. 134/2547-2559. https://doi.org/10.1007/s00122-021-03841-y.
Interpretive Summary: Grain hardness is a key physical trait that influences wheat milling and baking quality. Based on kernel texture, hexaploid wheat is classified as soft or hard class. Harder wheat kernels require higher more power to mill and thus, produce flours with larger particle size and higher levels of starch damage compared to softer kernels. The higher levels of damaged starch granules in flour absorb more water and therefore, these wheat classes have different intended products. Hard wheat flour is usually used for making pan breads whereas, soft wheat flour is used for making crackers, cookies, cakes, steam breads, and some Asian-style noodles. At least two large-effect QTL, QSKhard.wql-3A and QSKhard.wql-5A, were found to be associated with reduced hardness index in soft wheat to produce the super soft phenotype. Fine mapping and cloning of these two loci in future will improve our understanding of the genetic determinants of the super soft grain texture. Furthermore, we identified five small-effect QTL on chromosomes 1BL, 3BL, 4DL, 6BL and 7AS that can be pyramided with large-effect QTL to achieve the desired softness. Five of the identified QTL in this study, QSKhard.wql-3A, QSKhard.wql-3B, QSKhard.wql-4D, QSKhard.wql-5B, and QSKhard.wql-6B, were not previously reported to be associated with grain hardness.
Technical Abstract: Grain hardness is a key determinant of wheat milling and baking quality. The newly recently discovered ‘super soft’ kernel phenotype has the potential to improve wheat processing and flour quality. However, the genetic basis underlying the super soft trait in wheat is not yet well understood. In this study, we investigated the phenotypic and genotypic structure of the super soft trait in a collection of 172 advanced soft white winter wheat breeding lines and cultivars adapted to the Pacific Northwest-West region of the United States. This wheat collection had a continuous distribution for grain hardness index (Single Kernel Characterization System). We identified 10 super soft genotypes showing hardness index =12 including the cultivar Jasper. Over 98,000 SNP markers from genotyping-by-sequencing were used for association mapping (GWAS). The GWAS identified 24 significant markers associated with grain hardness. These significant SNPs corresponded to eight QTL on chromosomes 1B, 3A, 3B, 4D, 5A, 5B, 6B, and 7A. Three of these QTL QSKhard.wql-3A, QSKhard.wql-5A, and QSKhard.wql-5A on chromosomes 3A, 5A, and 5B, respectively, had large effects, whereas the remaining QTL had small effects. The epistatic interactions between the identified QTL showed that pyramiding the three large-effect QTL resulted in the highest greatest softening effect. QSKhard.wql-3A, QSKhard.wql-3B, QSKhard.wql-4D, QSKhard.wql-5B, and QSKhard.wql-6B were not previously reported to be in the genomic regions of grain hardness related genes/QTL. The identified super soft genotypes as well as the SNPs associated with lower grain hardness will be useful to assist breeding for this grain texture trait.