Biopriming with rhizosphere Trichoderma harzianum elicit protection against grapevine downy mildew disease by triggering histopathological and biochemical defense responses

The economic loss and the failure of the chemical control measures to impede downy mildew infection on the grapevine (Vitis vinifera L.) have led to the exploration of biocontrol agents that can effectively manage the invading disease by invoking defense responses of the host plant. Hence, the present study was aimed to explore the efficacy of the talc-based formulation of biocontrol agent Trichoderma harzianum to induce protection against oomycete pathogen, Plasmopara viticola (Berk et Curt.) Berl. et de Toni by triggering defense mechanisms in grapevine. The field study demonstrated that priming with T. harzianum led to the elicitation of defense responses in pathogen inoculated grapevines, with maximum disease protection up to 82.9% on the 4th-day. In addition, the microscopic observation of histochemicals revealed an increased accumulation of lignin, callose and hydrogen peroxide initiated at early 12 h and reached the highest at 24 h post-inoculation. Furthermore, the activities of the defense enzymes, namely, phenylalanine ammonia-lyase, peroxidase and 1,3-glucanase, were upregulated in the tripartite system between the course of tested time intervals. Overall, the findings from the present study highlighted the induced protection incited by T. harzianum in response to P. viticola infestation and witness the significant role of cellular and biochemical enzymes priming for defense in conferring protection against downy mildew disease in grapevine.