Abstract
Angular leaf spot (ALS) is one of the most devastating diseases of common bean (Phaseolus vulgaris L.) and causes serious yield losses worldwide. ALS resistance is reportedly pathotype-specific, but little is known about the efficacy of resistance loci against different pathotypes. Here, we report on ALS resistance evaluations of 316 bean lines under greenhouse and field conditions at multiple sites in Colombia and Uganda. Surprisingly, genome-wide association studies revealed only two of the five previously described resistance loci to be significantly associated with ALS resistance. Phg-2 on chromosome eight was crucial for ALS resistance in all trials, while the resistance locus Phg-4 on chromosome 4 was effective against one particular pathotype. Further dissection of Phg-2 uncovered an unprecedented diversity of functional haplotypes for a resistance locus in common bean. DNA sequence-based clustering identified eleven haplotype groups at Phg-2. One haplotype group conferred broad-spectrum ALS resistance, six showed pathotype-specific effects, and the remaining seven did not exhibit clear resistance patterns. Our research highlights the importance of ALS pathotype-specificity for durable resistance management strategies in common bean. Molecular markers co-segregating with resistance loci and haplotypes will increase breeding efficiency for ALS resistance and allow to react faster to future changes in pathogen pressure and composition.
Highlights
Plant diseases can cause substantial loss of crop yields with detrimental effects on food security (Oerke, 2006; Savary et al, 2012)
Through Genome-wide association studies (GWAS) in the largest yet assembled diversity panel segregating for Angular leaf spot (ALS) resistance, a pathotype-specific resistance locus, likely Phg-4, and a broad-spectrum resistance locus coinciding with Phg-2 were effective against a variety of ALS pathotypes from Colombia and Uganda
ALS resistance is reportedly controlled by five major resistance loci, named Phg-1 to Phg-5 (Souza et al, 2016)
Summary
Plant diseases can cause substantial loss of crop yields with detrimental effects on food security (Oerke, 2006; Savary et al, 2012). Breeding for ALS resistance is challenged by the high genetic diversity of the pathogen and the recurrent appearance of new P. griseola pathotypes (Pastor-Corrales et al, 1998; Busogoro et al, 1999; Mahuku et al, 2002a). To categorize pathotypes, they are tested for their ability to infect six Andean and six Mesoamerican common bean lines with distinct resistance patterns ( referred to as differentials), in order to determine their race (Pastor-Corrales and Jara, 1995; Nay et al, 2019). Resistance in common bean has been reported to be pathotypespecific with large differences of the effectiveness in different locations and continents (Pastor-Corrales and Jara, 1995; PastorCorrales et al, 1998; Mahuku et al, 2002b; Silva et al, 2008)
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