Determination of responses of different bean cultivars against races of Pseudomonas syringae pv phaseolicola, causal agent of halo blight of bean

Use of resistant plant varieties combined with other disease management practices is regarded as the most practical approach to control of seed-borne bacterial disease agents. In this study, responses of different bean cultivars to nine different races of Pseudomonas syringae pv phaseolicola, the causal agent of bacterial halo blight of common bean (Phaseolus vulgaris L.), were determined. During compatible interaction in susceptible cultivars, virulent bacterial races caused water soaked lesion at sites of inoculation. Similar lesions developed in moderately resistant cultivars but symptoms were later associated with more tissue browning around the sites of inoculation. In contrast, the resistant response, produced the characteristic hypersensitive reaction (HR), was characterized as a small discrete browning and tissue collapse at site of inoculation. No local cultivars showed complete resistance to all races tested. Bean cultivars Sehirali-90 and Göynük-98 were found to be resistant or moderately resistant to five different bacterial races. Bean cultivar, Karacaşehir-90, on the other hand, was found to be resistant or moderately resistant to six different bacterial races. Analysis of bacterial growth and the accumulation of isoflavonoid bean phytoalexin, phaseollin in planta were carried out for tissues expressing compatible and incompatible interactions to enable a link to be made between reaction phenotypes and restriction of bacterial growth and phytoalexin accumulations. Development of the HR was clearly associated with the restricted multiplication of bacteria during incompatible interactions. A time-course accumulation analysis on pods treated with different races of bacterial agent showed that a strong correlation was observed between the timing and extent of cell death and accumulation of phaseollin, being rapid and extensive in incompatible interactions compared to compatible interaction.