پراکنشXanthomonas hortorum pv. pelargonii عامل سوختگی باکتریایی شمعدانی در ایران

Geraniums, scientifically known as Pelargonium spp., are flowering plants belonging to the Geraniaceae family. These ornamental plants are highly valued for their economic significance and are widely cultivated around the world. Plant diseases are among the factors limiting the production of geranium plants. Bacterial blight caused by Xanthomonas hortorum pv. pelargonii is one of the most important damaging bacteria in geraniums. To determine the distribution of bacteria in the country, during the years 2020 and 2021, greenhouses producing geranium plants were surveyed in the Alborz, Isfahan, Kohgiluyeh Boyer Ahmed, Markazi, Fars, Tehran and Yazd provinces. Samples were collected from plants showing leaf spot and blight symptoms. The samples were transferred to the laboratory for pathogen isolation and diagnosis. Isolation of bacteria was done according to the usual methods in bacteriology on nutrient agar medium. Overall, 22 bacterial strains were isolated from symptomatic plants collected in all surveyed provinces except Yazd province. A number of the most important biochemical tests were performed to identify the bacterial strains. All bacterial strains were gram, oxidase, and urease negative. They were positive for esculine, casein, gelatin, and tween 80 hydrolysis. Furthermore, all strains were positive for induction of HR and produced necrotic lesions 24-48h post injection on tobacco plants. Based on the results of biochemical and physiological tests, the 22 strains isolated in this study were identified as members of the Xanthomonas genus. By amplifying the 777 bp fragment in all the strains using Xc-lip-F2/Xc-lip-R2 primers, the results of biochemical tests were confirmed. Further, the X. hortorum pv. pelargonii-specific primer pair XcpM1F/XcpM2R directed the amplification of the expected 197 bp DNA fragment in all 22 strains isolated in this study. To determine the phylogenetic position of the bacterial strains, two housekeeping genes gyrB and lepA were sequenced. The results of molecular analysis and phylogenetic tree construction indicated that the bacterial strains isolated in this study exhibit 100% similarity to X. hortorum pv. pelargonii and were separated from other pathovars of X. hortorum. Pathogenicity test of bacterial strains was evaluated on geranium plants under greenhouse conditions. Two weeks after inoculation, the typical symptoms of the bacteria appeared in the form of leaf spots with a yellow halo and blight on the edges of the leaves. The results of this study indicate that geranium bacterial blight is widely distributed throughout the country. One of the most important ways of widespread distribution of this bacterium is transmission through infected cuttings, therefore before propagating geranium plants, it is crucial to ensure that the cuttings are free from bacterial infection.