ویژگی‌های فنوتیپی، مولکولی و بیماری‌زایی Xanthomonas sp. جدا شده از درختان خرمالو

Persimmon, scientifically known as Diospyros kaki, belongs to the Ebenaceae family. It is distributed in various temperate and tropical regions around the world. Iran is among the top 10 persimmon-producing countries and ranked eighth globally with a production of 30,471 tons over 1,978 ha. In 2019, the leaf spot symptoms with a yellow halo were observed in persimmon trees. Samples were collected from the symptomatic leaves and transferred to the laboratory for isolating the disease agent and conducting phenotypic, molecular, and pathogenicity tests. Nutrient agar medium was used for bacterial isolation, and the Petri Dishes were kept at room temperature for 72-96 hours. After three days, pale-yellow, domed, and circular colonies grew on the nutrient agar medium. A number of the most important biochemical tests i.e. aerobic/anaerobic, gram, oxidase, urease, and hydrolysis of aesculin, casein, and tween 80 were performed. Hypersensitivity reaction was performed by injecting bacterial suspension into the leaves of tobacco plants. The results of the biochemical tests showed that the strains were obligate aerobic and the results of gram, oxidase, and urease tests were negative, while they were positive for aesculin, casein, and tween 80 hydrolysis, and induce of hypersensitive reaction on tobacco plants. Therefore, based on the results of biochemical tests, the strains were considered as Xanthomonas spp. Further investigation with specific primers of Xanthomonas genus (Xc-lip-F2/Xc-lip-R2) and amplification of 777 bp fragment in the strains, the results of biochemical tests were confirmed. Further studies using 16S rRNA gene sequencing revealed that these strains were grouped in the Clade-I of Xanthomonas. Therefore, to identify the species and accurately determine the phylogenetic position of bacterial strains, four housekeeping genes dnaK, fyuA, efp, and rpoD were sequenced and the concatenated tree was constructed by the Maximum Likelihood method using Mega software. The phylogenetic analysis results indicate that the bacterial strains isolated in this study belong to Clade-I of Xanthomonas and are closely related to X. translucens, X. theicola, and X. sacchari. The pathogenicity of isolates was assessed by spraying the bacterial suspension on persimmon seedlings under greenhouse conditions. After three weeks of inoculation, leaf spot and blight symptoms appeared on the surface of the leaves. Inoculated bacteria were re-isolated from symptomatic leaves. Therefore, based on these results, the bacterial strains obtained in this study are considered as Xanthomonas sp.