Abstract

Common bacterial blight (CBB), which is caused by Xanthomonas axonopodis pv. phaseoli (Xap), is the main bacterial disease in snap beans and controlling this disease using resistant cultivars is still a challenge. This work aimed to study the combining ability for CBB resistance in Phaseolus vulgaris genotypes. Six parents (two genotypes of CBB-resistant dry bean and four susceptible snap bean accessions) were crossed in a complete diallel scheme without reciprocals to estimate the general and specific ability to Xap resistance. CBB resistance was evaluated by the inoculation with two Xap isolates, and its severity was evaluated based on the four following resistance components: area under the disease progress curve; scores in the leaves; latent period and diameter of pod lesion. Differences between the two isolates were observed considering all the disease components. Besides pathogen variability, significant GCA and SCA indicate that additive and non-additive effects are involved in Xap-resistance control for the evaluated genotypes, implying that CBC resistance is a trait with complex inheritance. For breeding purposes, the result demonstrates the need to apply breeding methods that are focused on advanced generations selection.

Highlights

  • Snap and dry beans are crops that are taxonomically classified in the same botanical species, Phaseolus vulgaris L

  • The significant GCA and SCA indicate that additive and non-additive effects are involved in Xanthomonas axonopodis pv. phaseoli (Xap)-resistance control for the evaluated genotypes, implying that Crestamento Bacteriano Comum (CBC) resistance is a trait with complex inheritance

  • Rodrigues et al (1999) evaluated the inheritance of Common bacterial blight (CBB) resistance in the leaves and pods of snap and dry bean genotypes and only observed significant GCA effects for resistance in the leaves, while significant GCA and SCA effects were observed for Xap resistance in the pods

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Summary

Introduction

Snap and dry beans are crops that are taxonomically classified in the same botanical species, Phaseolus vulgaris L. The final product is the grain, which is an important protein source for populations in less developed areas in the world. The bush-type cultivars are derived from few genotypes, and some authors estimate that 76% of the bush snap bean germplasm is derived from the ‘Tendercrop’, ‘Blue Lake’ and ‘Harvest’ varieties (SILBERNAGEL et al, 1991; SOTIRIOU; MAVRONA, 2008; ZAUMEYER, 1972). This restricted genetic variability results in low productivity and high pathogen susceptibility (TRINDADE et al, 2011; VILELA et al, 2009)

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