Evaluation of Trichoderma harzianum and Serratia proteamaculans effect on disease suppression, stimulation of ROS-scavenging enzymes and improving tomato growth infected by Rhizoctonia solani

Rhizoctonia solani is one of the most devastating plant pathogen that affects major crops and causes considerable yield losses. The objectives of the present study were investigating the effect of the rhizobacteria Serratia proteamaculans against R. solani comparing to Trichoderma harzianum and examining the ability of the two biocontrol agents to induce the plant defence system as a mechanism to suppress R. solani infection. Preliminary screening shown that S. proteamaculans was able to inhibit R. solani in vitro while T. harzianum overgrown the pathogen. The two biocontrol agents were able to suppress R. solani infection by 61.4, 62.6, 61.6% in vivo when plants treated with T. harzianum, S. proteamaculans and their combination respectively. In addition, plant fresh weight and length measurements indicated that both biocontrol agents either alone or in combination were able to increase tomato seedling growth compared to control plants with no significant differences among treatments. Examination of the two biocontrol agents capability to induce the antioxidant enzymes in plants under stress revealed that the protection provided by the two biocontrol agents was associated with increasing activities of ascorbate peroxidase (APX), guaiacol peroxidase (GPX), superoxide dismutase (SOD) and catalase (CAT) at the early stage after pathogen challenges. All enzymes reached their maximum activities at day 7 after treatments by 3, 2, 4, 3 folds for APX, GPX, SOD and CAT respectively. The obtained results suggest that T. harzianum, and S. proteamaculans - mediated protection against R. solani may be associated with alleviation of oxidative burst in host cells. (C) 2016 Elsevier Inc. All rights reserved.