Induction of systemic resistance against Plasmopara viticola in grapevine by Trichoderma harzianum T39 and benzothiadiazole

Plasmopara viticola, the causal agent of grapevine downy mildew, severely affects grape yield and wine quality worldwide. Biocontrol agents and resistance inducers could be valid alternatives to chemical pesticides. We demonstrated the capability of Trichoderma harzianum T39 to protect susceptible grapevine cultivars (Vitis vinifera cv. Pinot Gris and cv. Pinot Noir) against downy mildew under greenhouse conditions. T. harzianum T39 reduced downy mildew severity on grapevine without a direct inhibition of P. viticola sporangia germination. Plant-mediated resistance was activated after preventive T. harzianum treatments, in a manner similar to that observed for benzothiadiazole (BTH) elicitation. Optimal disease control results were seen when BTH was applied 24 h before pathogen inoculation (83% disease reduction) and T. harzianum was applied more than once, 48–72 h before inoculation (63% disease reduction). Whereas leaves treated with the inducers were resistant to the disease, a systemic activation of grapevine defenses was also observed in untreated leaves. In particular, T. harzianum and BTH leaf treatments on one side of the plant activated disease protection, 60% and 56% respectively, in untreated leaves on the opposite side. Additionally, treatments of basal leaves induced acropetal resistance in untreated leaves (more than 40% disease reduction), but root treatments did not induce significant resistance in leaves. The systemic resistance was homogeneously activated, independently of leaf position on the shoots. Differences between T. harzianum T39- and BTH-induced resistance in time of activation, persistence of the effect and systemic protection suggested that in grapevine different pathways than those of salicylic acid-dependent BTH elicitation are activated by T. harzianum.