Differential responses of Phaseolus spp. against Black node disease (Boeremia noackiana)

Black node disease is one of the most limiting biotic stresses affecting bean production in the Andean countries. The objective of the study was to evaluate the degree of resistance to Boeremia noackiana against genotypes of Phaseolus vulgaris, Phaseolus polyanthus, and their interspecific crosses using two disease evaluation methods (pathogenicity test in the greenhouse and in vitro) to contribute the generation knowledge towards the use of durable resistance. Black node disease severity was assessed using a descriptive scale and the leaf detached method under greenhouse and in-vitro conditions. The results of the study confirmed the isolate Ascochyta ASC 001 pathogenicity, allowing the different genotypes to be discriminated. A contrasting resistance response was confirmed for the two methodologies used to estimate severity. Accession G35575 (P. polyanthus) was the most resistant whereas NCB 226 (P. vulgaris) was the most susceptible. Regional cultivars Simijaca and Cabrera, together with Cargamanto Blanco and Bacata, showed fluctuations in their reaction to the disease from intermediate to susceptible. Resistance was confirmed in the interspecific crosses of the ASC series, which can be an alternative in breeding programs for durable resistance in common beans. The percent leaf area affected was identified as a variable that can be easily assessed, and the processing and analysis of digital images in vitro avoided the use of destructive sampling. This technique is a fast, useful, and economical tool for this type of studies, as it provides the possibility of accelerating the selection of genotypes with resistance.