Quantitative trait loci underlying the adhesion of Azospirillum brasilense cells to wheat roots

The capacity to adhere Azospirillum brasilense cells on the seedling root is a variable trait in wheat varieties (Triticum aestivum L.). The parents of a CIMMYT bread wheat mapping population derived from the cross cv. Opata x synthetic hexaploid line WSHD67.2 (257) contrasted for this trait, providing an opportunity to determine its genetic basis. The capacity to adhere effectively was shown by 32 % of the mapping population individuals. A genetic map was constructed using 157 informative microsatellite loci and 1,356 SNP loci. The resulting quantitative trait loci (QTL) analysis identified four chromosomes as harboring loci associated with adhesion. Chromosome 1A was the site of both a major (LOD > 3) and a minor (LOD 2-3) QTL, while the remaining four minor loci mapped to chromosomes 2D, 5A and 6B (two loci). QAdh.uabcs-1A.2 explained 8.6 % of the phenotypic variance and the full set of QTL explained 23.1 %. The source of the positive allele of QAdh.uabcs-1A.2 was cv. Opata. The recognition that adherence has a genetic component has consequences for the use of biofertilizers, and opens the way for breeding for improved levels of A. brasilense adherence.