Phenotypic Diversity of Causal agent Strains of Potato Common Scab (Streptomyces sp.) in Chaharmahal va Bakhtiari Province

Common scab is one of the most important diseases in the potato fields caused by several species of bacteria of the genus Streptomyces. Symptoms and severity of common scab of potato caused by different factors, is different. The control also will be different.
About 500 samples of potato tubers with common scab symptoms were collected from different regions in Charmahal VA Bakhtiari province during 2009 and 2010. Isolation of causal agent was performed by standard methods, then the isolates were studied, using biochemical, physiological and nutritional standard test. Thus, the color of the colony and spore mass color YMEA medium after 10 to 14 days were examined. The Gram staining reaction was conducted by Suslow et al. (34). Aerobic and anaerobic growth test (O / F) in the presence of glucose was done by Hugh and Leifson (14). The isolates ability to use sugars (L-arabinose, D-fructose, D-glucose, D-mannitol, raffinose, sucrose, cellulose, D-xylose, rhamnose and mesoinositol) and amino acids were investigated by Faucher et al method (6). Toxic substances inhibiting bacterial growth were evaluated in culture medium malt and yeast extract containing potassium tellurite (10 and 100 micrograms per ml), thallium acetate (10 and 100 micrograms per ml), crystal violet (0.5 g ml) and phenol (0.1%) by Lambert and Loria method (23). Using lysosomes, total protein of 14 isolates representing of different phenotypes groups and two reference strains of S. acidiscabies and S. scabies, were extracted by Paradis et al. (29), and their diversity was investigated by acrylamide gel electrophoresis contain dodecyl sulfate (SDS) according to Laemmeli (22) The pathogenicity of isolates was evaluated by inoculation of radish and potato tubers Schaad et al. (30) method. Isolates were amplified by spore inoculation in the flask containing 100 grams of vermiculite saturated with nutrient solutions (20 g of sucrose, 2.1 grams of L-asparagine, 0.6 g of potassium phosphate and 10 grams of yeast extract per liter of water) and two weeks incubation was conducted at 30 C˚.
Collectively, 55 bacterial (Streptomyces) isolates were obtained that were divided into six phonotypical groups by standard phenotypic tests. Characteristics of isolates in the first group were very similar to S. stelliscabies and S. europaeiscabies, but were varied in a few characters. The isolates of the second group with the minimum variety were distinguished as S. scabies. Many characters of isolates in the third group were similar to S. acidiscabies. The fourth groups of isolates were similar to S. turgidiscabies and S. aurofaciens. The isolates of fifth group were very variable. The sixth groups of isolates were similar to S. griseus, but differed in some characters. In pathogenicity tests, 46 isolates were created disease symptom on radish seedlings, but among of 26 isolates inoculated to potato, 22 isolates were caused different scab symptoms. Total protein of 14 isolates from different phenotypic groups and two strains of S. acidiscabies and S. scabies were extracted and appeared on an electrophoresis gel by Laemmli (1970) method. Analyses of protein pattern were differentiated 14 isolates to five clads. Although, the isolates classified in one, two and three phenotypic groups were also classified in three distinct clads, but isolates in others phenotypic groups were shown variable patterns and did not place in distinct clads. For example, the reference strain S. acidiscabies with the 18E-2, 28-R, 12-R isolates belonging to a third phenotypic group, and reference strains of S. scabies with 15-E, 26-E and 22-R isolates belonging to the second phenotypic group, were differentiated in the first and second protein pattern groups, respectively. But isolates of 2-D and 16-4 (six phenotypic group) and 26-E-1 (four phenotypes group), were placed in the fourth protein group that were different with the results of the phenotypic tests.