To control strawberry root rot disease, inocula or suspensions of 3 bacterial isolates (i.e., Bacillus subtilis, Pseudomonas fluorescens, Streptomyces aureofaciens) and the fungus Trichoderma harzianum were evaluated against 3 root rot fungi (i.e., Sclerotium rolfsii, Rhizoctonia solani and Rhizoctonia fragariae). The in vitro antagonistic effect of B. subtilis, T. harzianum and P. fluorescens on root-rot pathogens revealed the presence of clear antagonistic action between them. The highest mean inhibition in linear growth was 40.7, 36.6 and 26.6% against R. solani, S. rolfsii and R. fragariae with B. subtilis, respectively, followed by 38.8, 38.8 and 29.6% against R. solani, R. fragariae and S. rolfsii with T. harzianum. Meanwhile, the lowest was 33.7 and 31.0% against R. solani and S. rolfsii with P. fluorescens, but no effect with S. aureofaciens. Dipping the strawberry roots in suspensions of the tested antagonists prior sowing in artificially infested soil with 3 pathogens under greenhouse enhanced the percentage of survival plants. The highest value was recorded with T. harzianum followed by B. subtilis and P. fluorescens, but the lowest was noticed with S. aureofaciens compared with the control. In addition, strawberry shoot and root lengths were enhanced in response to the same treatments with almost equal effect over the control. Lignin content in the strawberry roots was conspicuously increased in response to dipping roots in suspensions of the 4 tested inducers in comparison to the control especially with P. fluorescens, followed by B. subtilis, S. aureofaciens then by T. harzianum against R. fragariae followed by R. solani and S. rolfsii, respectively. Pathogenesis related enzymes in roots were increased in response to dipping in the suspension of 4 biotics. Peaks of peroxidase, polyphenoleoxidase, chitinase and ,1-3-glucanase activities were differed against the 3 tested pathogens, however, present clear evidence dealing successfully systemic or local induction resistance against the root rot pathogens. Under field conditions, strawberry roots dipped in the suspensions of 4 tested antagonists prior sowing in the soil naturally infested with root-rot pathogens. The highest survival plants percentage was recorded with of T. harzianum followed by S. aureofaciens and B. subtilis, but the lowest was by P. fluorescens as compared with the control.
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Key words: Strawberry, biotic inducers, root-rot, Rhizoctonia, Sclerotium, shoot and root length, lignin content, enzyme activities