Abiotic stresses affect Trichoderma harzianum T39-induced resistance to downy mildew in grapevine

Enhancement of plant defense through application resistance inducers seems a promising alternative to chemical fungicides for controlling crop diseases, but the efficacy can be affected by abiotic factors in the field. Plants respond to abiotic stresses with hormonal signals that may interfere with the mechanisms of induced systemic resistance (ISR) to pathogens. In this study we exposed grapevines to heat and/or drought to investigate the effects of abiotic stresses on grapevine resistance induced by Trichoderma harzianum T39 (T39) to downy mildew. Whereas the efficacy of T39-induced resistance was not affected by exposure to heat or drought, it was significantly reduced by combined abiotic stresses. Decrease of leaf water potential and up-regulation of heat-stress markers confirmed that plants reacted to abiotic stresses. Basal expression of defense-related genes and their up-regulation during T39-induced resistance were attenuated by abiotic stresses, in agreement with the reduced efficacy of T39. The evidence reported here suggests that exposure of crops to abiotic stress should be carefully considered to optimize the use of resistance inducers, especially in view of future global climate changes. Expression analysis of ISR markers genes could be helpful to identify when plants are responding to abiotic stresses, in order to optimize treatments with resistance inducers in field