Alleviation of black root rot symptoms and alteration of strawberry growth via modulating physiological and biochemical mechanisms using Trichoderma viride and Bacillus subtilis

The effectiveness of Trichoderma viride and Bacillus subtilis to protect strawberry against black root rot disease under the greenhouse and field conditions was investigated. In in vitro bioassays, the two microorganisms exhibited strong capabilities to antagonize the pathogen Rhizoctonia fragariae. Soil amendment with T. viride at rate 50 ml/ plant (1 x 10(7)/ ml) conidial spore and B. subtilis at rate 50 ml/ plant (1 x 10(8) / ml cfu) separately or in combination ameliorated the disease symptoms, enhanced plant growth parameters reaching 1.2 and 1.6 fold for shoot and root growth in greenhouse, whereas the growth enhancement reached 1.2 and 1.5 fold for shoot and roots growth in the field. Consequently, fruit numbers was increased by 2 and 4 fold for plants grown in the greenhouse and fields , respectively. Further biochemical evaluation revealed a substantial increase in ethylene signals at day 2 and 4 and remained high at day 7 after treatment under greenhouse and field conditions, whereas the accumulation of hydrogen peroxide (H2O2) was decreased at day 2 after treatment compared with pathogen infected plants. Furthermore, T. viride and B. subtilis application ameliorated ion leakage damage in infected plants whereas lipid peroxidation decreased significantly resulting in maintaining cell membrane integrity. In addition, examination of the capability of the two microorganisms to enhance the antioxidant enzymatic activities exhibited a significant increase of superoxide dismutase (SOD) and catalase (CAT) activities on day 4, 5 and 6 after treatments. These results suggest that the application of T. viride and B. subtilis as soil amendment provides a significant protection against R. fragariae and improves plant growth parameters and fruit numbers. However, the combination of the two bioagents did not provide additional protection.