اولین گزارش بیماری لکه باکتریایی آفتابگردان (Pseudomonas syringae pv. helianthi) از استان آذربایجان‌غربی

In order to isolate the causal agent of sunflower bacterial spot disease, in 2023-2024, samples were taken from this crop fields in West Azerbaijan province from Urmia and Naqadeh. After isolating and culturing the infected samples on nutrient agar medium containing sucrose, a cream-colored, gram and oxidase-negative and Levan-positive bacteria was isolated which produced fluorescent green pigment on the King's B medium, meanwhile demonstrated negative results in the pectinase and arginine dihydrolase tests on the other hand it displayed positive results for tobacco hypersensitivity reaction, which indicates that they belongs to group Ia of Pseudomonas. To identify bacteria by phenotypic methods, biochemical, physiological and nutritional tests were performed in the manner of standard bacteriological methods. To carry out the pathogenicity test and ascertain the host range, the isolates were injected into peach, nectarine, tomato, wheat and sunflower hosts, and after three to four weeks in greenhouse conditions, the intended isolates were pathogenic only on sunflower the symptoms of the disease initially appears as chlorotic spots as virus like symptoms which progress into extensive necrotic lesions at leaf edges, progressing toward the center of the leaf. For genotypic identification, the DNA of the selected isolates were extracted and after amplification of 16s rRNA and rpoD genes, they were sent to Cinagen company for sequencing. The obtained sequences were compared with other sequences in the gene bank, and based on that, a phylogenetic tree was drawn. The consequences demonstrated which isolates from sunflower had more than 99% similarity to the standard strains of Pseudomonas syringae pv. helianthi and also were placed in another group separately with other Pseudomonas species in the drawn phylogenetic tree. According to all the phenotypic, pathogenicity and genotypic tests, the isolates were identified as P. syringae pv. helianthi, the causal agent of sunflower bacterial spot disease in West Azarbaijan province. This is the first report of the isolation and identification of this pathovar in Northwest of Iran as the causal agent of sunflower bacterial spot disease.