Characterization of Trichoderma harzianum T39 induced resistance against Plasmopara viticola in heat and drought stressed grapevine plants

Plants can acquire an enhanced defensive capacity after treatment with a resistance-inducing agent that results in a faster and/or stronger defence reaction against pathogens. These agents induce a broad spectrum and long lasting resistance, but rarely provide complete control of infections (for the most part between 20 to 85% of disease control). Under field conditions, the expression of induced resistance is often inconsistent and likely to be influenced by the environment, plant genotype and its physiology. However little information is available on the role of these factors on the level of induced resistance. Since abiotic stresses may strongly influence the host plant, the aim of this project is to investigate the effect of a short heat and/or drought exposure of grapevine plants on the systemic resistance activated by Trichoderma harzianum T39 (T39) or benzothiaziadole (BTH) against downy mildew (Plasmopara viticola). In susceptible grapevine cultivars grown under controlled greenhouse conditions, foliar treatments with T39 or BTH reduce disease severity. Gene expression analysis indicates the activation of jasmonic acid and ethylene signal in the defence induced by T39, while salicylic acid pathway is activated by BTH. The pre-exposure of plants to drought and/or heat stress (abiotic stress) did not affect the efficacy of BTH-activated resistance. On the contrary, the T39-induced resistance was influenced by the plant pre-exposure to the above mentioned abiotic stress conditions, showing different levels of downy mildew reduction. The results indicate that T39-induced resistance might be a useful tool in the control of downy mildew, but, even if its efficacy level is not affect by the genotype, it can be modulated by the physiological state of the plant. Further characterization of molecular events of T39-induced resistance under abiotic stress exposure could be particularly important in order to predict the possible effect and stability of T39-induced resistance under field condition especially in a view of climate change.