Combination of Biocontrol Agents for Controlling Soybean Damping-off Caused by Rhizoctonia solani

Soybean seeds (cv. Giza 22) were treated with Paenibacillus polymyxa, Pseudomonas fluorescens and Mycorrhizeen
compound (contains mainly endospores of Glomus sp.) as biocontrol agents either individually or in different combinations to study their effect on the infection with Rhizoctonia solani under greenhouse and field conditions. Treatment of Rizolex-T 50% was also applied to compare the output data. Under greenhouse conditions, all the treatments significantly reduced the percentages of pre and postemergence damping-off and increased survived plants compared to untreated control grown in infested soil by R. solani. The highest percentage of survived plants 92% was achieved from the triple
combination treatment (Mycorrhizeen plus P. polymyxa and P. fluorescens) and Rizolex-T treatment as compared to the untreated control, which achieved 48%. The significant increases in plant height, shoot dry weight and root dry weight of soybean plants were recorded with the triple combination treatment followed by the fungicide treatment. Meantime, all treatments significantly enhancing both number of nodules/plant and total dry weight of nodules/plant compared with untreated control grown in infested soil by R. solani. The maximum increase was observed with triple combination
treatment followed by the dual combination of (Mycorrhizeen plus P. fluorescens) then Mycorrhizeen. In addition, the results showed that combined treatments enhanced the percentage of colonization of  mycorrhizae in the roots over Mycorrhizeen sole treatment as 18.7% for the triple combination treatment. Under field conditions at two locations, Giza and Etai El-Baroud Agric. Res. Stat. during the summer of 2017 growing season, the triple combination treatment
resulted in high values of disease control near to that obtained with Rizolex- T treatment. Such an effect was true for pre and postemergence damping-off as well as the percentage of survived plants. Meantime, all treatments significantly showed stimulatory effect for crop parameters of soybean plants i.e. plant height, number of branches/plant, number of pods/plant, seed weight (g)/plant and seed yield (kg/feddan) compared to the untreated control treatment in the
two locations. The activity of oxidative enzymes and phenolic compounds contents were determined in soybean plants treated with the different bio-agents either individually or in different combinations. All treatments increased the peroxidase (PO), polyphenol oxidase (PPO) and phenolic content in the treated soybean plants over the untreated control plants sown in infested soil with R. solani. The maximum increase in the activity of both enzymes and phenolic contents was recorded with the triple combination treatment followed by the two dual treatments of the Mycorrhizeen.