Biological control of Rhizoctonia solani damping off of sugar beet with native Streptomyces isolates under greenhouse and field conditions

Biological control of sugar beet damping-off of Rhizoctonia solani AG-4 by two native Streptomyces isolates (S2 and C) was evaluated in green house and field conditions. In dual culture, two Streptomyces isolates inhibited mycelial growth of R. solani AG-4. Besides, volatile components of S2 and C inhibited R. solani mycelial growth for 72 and 74 percentages, respectively. Soil treatment either with isolate S2 or C inhibited Rhizoctonia damping off in sterilized soil inoculated with the fungal pathogen. Isolate C increased plant stand for 76 percentages and was more effective than S2. To elucidate the mode of antagonism, chitinase activity and siderophore production were evaluated. Both isolates showed chitinase activity on medium containing colloidal chitin and biosynthesis of siderophore was detectable for both isolates. A three- year study (2005- 2007) was conducted to evaluate the effectiveness of S2 and C on control of sugar beet Rhizoctonia solani damping off under field conditions. Streptomyces seed treatments significantly (p≤0.05) reduced seedling damping off compared to untreated control in naturally (2005) and artificially (2006 and 2007) infested soils. There was no significant difference between the isolates in disease control. Seed treatment with Streptomyces isolates reduced root rot significantly (p<0.05). In 2006 and 2007, the bacterial isolates increased healthy beets up to 80% and 95%, respectively.