تعیین مشخصات عامل بیماری سوختگی باکتریایی برگ‌های پیاز در استان اصفهان

In recent years, a bacterial blight disease affecting onion leaves has become more prevalent in the Feridan region of Isfahan province, leading to significant impact on onion products. The disease commences with the appearance of white oblong spots, which later develop into water-soaked and necrotic lesions, ultimately resulting in strip blight on the leaves. Through the individual culturing of white oblong, water-soaked, and necrotic spots on nutrient agar and King’B medium, a gram-negative bacterium was isolated from all samples. This bacterium displayed cream fusiform colonies that were non-fluorescent and exhibited slow growth characteristics. The homogeneity of the isolates was evident as they displayed similar banding patterns in both ERIC and BOX fingerprinting methods. Upon inoculating of the suspension of representative isolates onto the foliage of onion, garlic, and leek, white spots appeared within two weeks, followed by the development of necrotic spots. The analysis of the 16S rRNA sequence, in addition to housekeeping genes such as gyrB, rpoD, glt1 and the coronatine producing gene (cfl), revealed that the isolates share over 99% homology with the sequence of Pseudomonas coronafaciens, formerly known as P. syringae pv. coronofaciens. Members of the Poaceae plant family are the primary targets of P. coronafaciens. Similarly, the strains examined in this study had the ability to induce the appearance of white spots on the leaves of wheat, barley, oat, and rye in a greenhouse condition, which later progressed into brown spots. Given the inability to generate fluorescent pigment on King’B medium, a trait typically associated with P. syringae pathovars, and the isolates' capacity to induce pathogenicity on members of the Poaceae family and Allium sp., it is more reasonable to identify P. coronafaciens as the causative agent responsible for the bacterial disease affecting onion leaf blight in Isfahan region.