The efficacy of Pythium oligandrum in the biological control of Rhizoctonia solani, the causal agent of sugar beet damping-off under greenhouse conditions

Sugar beet is one of the most important crops in Iran. Damping-off, root rot and leaf blight diseases caused by Rhizoctonia solani (Kuhn) rank first in sugar beet yield reduction. Since soilborne fungi chemical control have ecological consecutions, therefore in this study, six strains of Pythium oligandrum were isolated from sugar beet fields soil in Khorasan Razavi province to be used as biological control agents. These isolates have already shown 32.09-71.36inhibitory effect on R. solani under laboratory conditions. Selected isolates were evaluated using pasteurized and non-pasteurized soil under greenhouse conditions, by adding antagonistic fungi to the soil and seed coating with oospore (seed treatment) methods. This study was consisted of five separate experiments with five to six treatments each with four replicates.t. All experimrnts were conducted in a randomized complete block desgin. The results showed that among the antagonists Torbat-jam isolate had the most reducing effects on sugar beet damping-off disease. Adding P. oligandrum inoculum to the soil containing R. solani increased sugarbeet seed germination compared to the control and reduced the damping-off disease in both pasteurized and non-pasteurized soil by 66% and 36% respectively. Sugarbeet seed coating by oospores of P. oligandrum increased sugarbeet seed germination while reduced damping-off disease in both pasteurized and non-pasteurized soil by 64 and 43% respectively.