جداسازی و شناسایی گونه های Streptomyces از مزارع و انبارهای سیب زمینی خراسان رضوی

Potato is an agricultural product that creats employment, provides food security and ranks in fourth level after corn, wheat and ric from viewpoint of nutrient value. One of the frequent potato diseases is common scab causes by several members of the genus Streptomyces. Nowadays this disease is found in all regions of Iran. Therefore, it is necessary to identify and study the disease factors in orderto control it. The present study is conducted to isolate the casual bacterial agent and to confirm the phenotypic, molecular and pathogenicity of Steptomyces strains obtained from potato. In the current research, symptomatic potato samples are gathered from potato farms and warehouses in different parts of Razavi Khorasan in 2017. Isolation of 34 strains is done from potatoes with superficial, erumpent and deep pitted lesions on the SCA medium. Pathogenicity and the ability to produce thaxtomin of the studied strains are carried out on radish seedlings and potato cuttings, respectively, according to common methods. Different phenotypic characteristics of the strains and detection of txtAB, tomA and nec1 genes are also investigated. representative strains are evaluated for pathogenicity on Agria potato tubers under greenhouse conditions. Molecular identification of the strains is performed by of 16s RNA sequencing. Twenty out of 34 strains are able to induce dwarfing, necrosis and in some cases hypertrophy on radish seedlings and necrosis on potato slices. Based on phenotypic characteristics such as the formation of spore chains, colony and spore color on the YME medium, penicillin susceptibility, melanin pigment production on the TSB medium, tolerance to different amounts of salt and growth in variable pH according to bacteriological references , the strains are placed in six groups. The presence of txt AB, tomA and nec1 genes have no identical pattern in in different strains. In the greenhouse, after three months symptoms of common scab are noted on potato tubers. Regarding to biochemical and physiological tests, pathogenicity assays in greenhouse conditions and sequencing of 16s RNA gene, candida strains are most similar to Streptomyces scabies, S. turgidiscabies and S. europaeiscabies.