Trichoderma atroviride TRS25 isolate reduces downy mildew and induces systemic defence responses in cucumber in field conditions

In an attempt to reduce the impact of downy mildew progress during cucumber cultivation and to improve plant growth, the efficacy of bio-agent Trichoderma atroviride TRS25 was evaluated in open field conditions. Two application forms of TRS25 were used: (i) dried conidia for seed coating, (ii) fungal biomass on organic carrier for soil application. The experiment was conducted for three years. The effect of TRS25 on cucumber germination, early plant growth, cucumber yield, rhizosphere colonization and downy mildew development were measured. To confirm the early evidence of induced resistance in plants caused by TRS25, the changes in hydrogen peroxide, lipid peroxides, phenolic compounds concentrations and the phenylalanine ammonia lyase, guaiacol peroxidase and ascorbate peroxidase activities in plant leaf tissues were estimated. Seed coating with TRS25 significantly improved cucumber germination, enhanced vegetative plant growth and reduced downy mildew infection, compared to untreated plants. Soil application of Trichoderma with organic carrier was disadvantageous for cucumber production, because of phytotoxic effect of the carrier. However, both forms of TRS25 application significantly reduced downy mildew and activated systemic defence responses in cucumber plants. The fungus was also able to colonize the rhizosphere. The results suggest that T. atroviride TRS25 may be used to improve plant resistance in integrated plant protection program.