No abstract

Background Plasmopara viticola, the causal agent of grape downy mildew, is one of the most serious grape diseases. Application of Trichoderma harzianum grown on different potato dextrose supplemented broth media using some chemical inducers (TSDCIS), i.e., thiamine (T2), a mixture of micronutrients (T3) and potassium tartrate (T4), compared to Trichoderma without amendment (T1), was conducted under field conditions to evaluate the potential of T. harzianum against grape downy mildew, improving the growth, as well as the yield quality, and quantity. Results Foliar application of all TSDCIS significantly reduced the disease severity and increased the phenolic content, peroxidase, polyphenol oxidase enzyme activity, growth parameters, and yield parameters. Trichoderma growing on medium supplemented with potassium tartrate (T4) achieved the most significant reduction in the disease severity (78.9, 81.8%) than the control treatment in two growing seasons, respectively. In contrast, it decreased H2O2 content, lipid peroxidation, and cellular electrolyte leakage. Scanning electron microscopy observations revealed that the number of opened stomata, average stomatal area, and stomatal pore area decreased significantly in response to T4 treatment. Conclusions It can be concluded that using Trichoderma growing on medium supplemented with potassium tartrate (T4) to biosafety control the downy mildew disease of grape and improve its growth, yield, and fruit quality is recommended.