Common bean (Phaseolus vulgaris) is a rich source of protein, vitamins, and micronutrients and is an important crop for food security throughout Latin America, Asia, and Africa. Among tropical and subtropical regions of the world, where the majority of beans are grown, yield losses due to the pathogenic fungus Pseudocercospora griseola, causing angular leaf spot (ALS), can be as high as 80%. The strategic use of marker-assisted selection (MAS) to pyramid multiple resistance genes into a single genetic background with preferred morphological and cooking characteristics is being implemented by six research groups throughout East Africa that make up the African Bean Consortium (ABC). Identifying unique markers that are polymorphic among multiple parents is a major source of marker attrition. In this study, an illustration of how 22 DNA sequences physically linked to the Phg-2 ALS resistance locus were identified using the PhaseolusGenes marker database and checked for amplification and polymorphism among 16 ABC breeding parents are given. Only three polymorphic markers could be identified following this procedure; one (g796), showed a polymorphism present only in the ALS resistance donor, Mexico 54. The PCR protocol developed to identify the g796 polymorphism was validated among five laboratories. Furthermore, co-segregation analysis of the marker and ALS resistance phenotype in a population of 100 F2 individuals from the cross between French bean (that is, green bean) genotype Amy and ALS resistance donor Mexico 54 showed the marker is genetically linked (3 cM) to the Phg-2 locus, in addition to being physically linked. This study suggests that in the near future, genetic resequencing data of diverse common bean accessions, compiled within an easily accessible database, will facilitate identification of markers for MAS, marker/trait association, and candidate gene identification.
Key words: Angular leaf spot resistance, Phaseolus vulgaris, marker-assisted selection.
ABC, African Bean Consortium; ALS, angular leaf spot; BLAST, basic local alignment search tool; InDel, insertion-deletion; MAS, marker-assisted selection; PAMP, pathogen associated molecular pattern; PCR, polymerase chain reaction; PTI, PAMP triggered immunity; RAPD, random amplification of polymorphic DNA; SCAR, sequence-characterized amplified fragment; SNP, single-nucleotide polymorphism; SSR, simple sequence repeat; STS, sequence-tagged site.
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