White mold resistance: association mapping and QTL identification in common bean

Oritsesaninormi Blessing Oraguzie

White mold, incited by Sclerotina sclerotiorum, Lib. de Bary, is a major disease, limiting common bean (Phaseolus vulgaris L.) production around the world. The effect of white mold disease on beans can be profound, causing a significant decrease in yield. There is little genetic diversity for white mold resistance in the Phaseolus vulgaris gene pool and genetic control appears to be complex, or quantitative with low to moderate heritability. Understanding the genetic mechanisms underlying the partial resistance would facilitate the development of new bean cultivars that are resistant to white mold (WM). The objectives of this research were to i) use association mapping in the Middle American diversity panel (MDP) consisting of ~300 accessions to identify novel QTL for partial resistance to white mold, and ii) validate the presence of QTL conferring partial resistance to white mold in a backcross RIL population consisting of ~100 F5:7 derived lines (Orion//Orion/R31-83). In the MDP population, principal component analysis was performed using the Tassel software to identify population structure and along with the kinship matrix was used as covariates in multiple linear models (including Naïve, GLM and MLM approaches) to identify marker-locus-trait associations. For all traits analyzed, 26 SNPs were significantly associated with 29 quantitative trait loci (QTL) spanning the eleven bean linkage groups (chromosomes). These SNPs satisfied the 0.01 percentile (p-value ≤ 5.58E-04) significance threshold. Although, association mapping in the MDP identified significant QTL conditioning resistance to white mold, further validation of the QTL may be warranted. For the RIL population, monomorphic and low-quality SNPs were filtered out in Genome Studio software leaving a total of 1,130 polymorphic SNPs. However, only 347 SNP were used for QTL analysis and detection due to co-localization of SNPs on the linkage maps. The Icimapping software was used to construct linkage maps while the WinQTLCartographer was used for QTL analysis. A total of eight putative QTLs were detected corresponding to five genomic regions on the eleven bean linkage groups (LG). The LOD values for the QTL ranged from 2.8 to 3.5, explaining between 6.7 to 19.2% of the phenotypic variance of the traits.

White mold resistance: association mapping and QTL identification in common bean

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