Identification of a novel source of resistance to angular leaf spot disease of common bean within the secondary gene pool

Phaeoisariopsis griseola (Sacc.) Ferr., the agent of angular leaf spot dise ase of common bean, is a highly variable pathogen for which resistance gene diversification is required. This study analysed genetic resistance to thi s disease within genotypes of three Phaseolus species. Twenty-nine genotype s of Phaseolus vulgaris, Phaseolus coccineus and Phaseolus polyanthus were inoculated with 54 isolates of Phaeoisariopsis griseola. The genetic resist ance was estimated according to the symptom intensity observed for each pla nt genotype-pathogen isolate combination. Globally, genotypes of the common bean secondary gene pool were resistant to a higher number of isolates tha n common bean varieties. Interactions between plant genotypes and pathogen isolates suggested vertical resistance genes within P. vulgaris, as well as within P. coccineus and P. polyanthus. The 'NI666' accession (P. coccineus ) showed resistance to all the fungal isolates inoculated while the variety 'Aroana' (P. vulgaris) was susceptible to most of the isolates. Interspeci fic hybridization between these two genotypes gave F-1 hybrid plants which showed resistance to angular leaf spot disease.