Pathotype-Specificity of Angular Leaf Spot in Common Bean - Genome Wide Association Studies and Implications for Resistance Breeding in Latin America and Africa

Abstract

Common bean (Phaseolus vulgaris L.) is an important food security crop because of its high protein level and affordable price. However, beans are frequently attacked by pests and diseases. One of the most devastating fungal bean diseases is angular leaf spot (ALS), responsible for yield losses of up to 80%. Although pathotype-specificity of ALS resistance has been reported in common bean, little is known about the efficiency of resistance loci against different pathotypes. Here we conducted GWAS for ALS resistance in a large diversity panel of common bean. Surprisingly, only two of the five previously described resistance loci were found to be significantly associated with ALS resistance when tested with pathotypes from Colombia and Uganda in the field and greenhouse. The resistance locus on chromosome 4 was effective against one particular pathotype, while the resistance locus on chromosome 8 was effective in all trials. The latter locus was further dissected to characterize the haplotype-specific effect on ALS resistance: Of the eleven haplotypes at this locus, one haplotype was conferring broad-spectrum resistance and six haplotypes were showing pathotype-specific effects. To the best of our knowledge, our study is the first to describe ALS resistance in such a diverse panel of common bean, tested with an extensive diversity of pathogen isolates on two continents. Our research also highlights the importance of understanding ALS pathotype-specificity to enable durable resistance management strategies for common bean. Molecular markers co-segregating with resistance loci or haplotypes will facilitate breeding for pathotype-specific ALS resistance.