Biological control agents improve the productivity and induce the resistance against downy mildew of grapevine

Downy mildew of grapevine, caused by Plasmopara viticola, is a foliar disease of global importance. Control of downy mildew of grapevine (Roumy Ahmar cultivar) using Streptomyces viridosporus, S. violatus, Trichoderma harzianum, T. viride and the commercial yeast of Saccharomyces cerevisiae was investigated. In addition to the disease control, all treatments significantly enhanced the plant growth, nutrient content, total phenol, activities of antioxidant enzymes, yield and fruit quality. Changes in some physiological and anatomical characteristics of the treated plants were also recorded. Compared to the control treatment, the maximum reduction of the disease severity (67.3%) was achieved by S. viridosporus or T. harzianum, while the best growth and yield parameters were recorded for S. violatus. Treatment of S. viridosporus showed the highest total phenol content (66.3%) as well as the highest activity of the antioxidant enzyme peroxidase (45.8%), over the control. S. violatus increased the contents of nitrogen (10.2%), phosphorus (37.2%), potassium (7.3%), and total soluble sugars (26.5%) in grapevine leaves over the control. Moreover, all treatments led to an improvement of the leaf anatomical features. In this regard, the treatment of S. violatus led to the increment of the thickness of mid-vein (47.1%) and lamina (56.8%) of the grapevine leaf blade over the control. Based on their efficiency and eco-safety, we recommend the use of S. viridosporus or T. harzianum for control of the downy mildew disease of grapevine, as well as to improve its growth, yield, and fruit quality.