شناسایی باکتری عامل سوختگی برگ و غلاف لوبیا در استان مرکزی

During the summer of 1998, leaf and pod blight symptoms of bean were observed in Arak, The survey in the following year showed that the disease had an increasing trend in bean-growing regions of Markazi Province. It appeared that more severe losses occurred in fields equipped with sprinkler irrigation system. Symptoms of diseased plants consisted of formation of irregular necrotic lesions on leaves surrounded by yellow halo. Under favourable conditions, these lesions gradually expanded and heavily infected leaves became blighted. The primary symptoms on infected pods were the development of water soaked spots which later turned to dark or reddish blotches. In attempts to investigate the causal agent, two types of a Gram negative bacteria with raised, yellow and translucent colonies were isolated from leaves and pods of blighted beans. All strains produced Xanthomonadin pigment and their inoculation on young bean plants induced disease symptoms similar to those observed under field conditions. Based on morphological, physiological and biochemical properties, the predominant pathogenic type was identified as Xanthomonas axonopodis pv. phaseoli. However, the other strain with the same properties, but capable of producing melanin pigment in nutrient media, was assigned to X. axonopodis pv. phaseoli var. fuscans.