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.
Xanthomonas axonopodis pv. phaseoli; disease-resistance inheritance; genetic effects; general and specific combining ability
) and standard deviations (SD) between two parents for four components of resistance to common bacterial blight (AUDPC = area under the disease progress curve; Score = average of the scores attributed to the advance of the disease over time; LP = Latent Period; DLP = diameter of the lesion in pods) evaluated in six parents of Phaseolus vulgaris L. intercrossed in diallel and inoculated with the isolates 1394-98 and 775-90 of Xanthomonas axonopodis pv. phaseoli.
achieved for four components of resistance to common bacterial blight (AUDPC = area under the disease progress curve; Score = average of the scores attributed to the advance of the disease over time; LP = Latent period; DLP = diameter of the lesion in pods) evaluated in six parents and 15 hybrids of Phaseolus vulgaris L. inoculated by the isolate 1394-98 of Xanthomonas axonopodis pv. phaseoli.
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