Magnesium carbonate elicits defense-related genes in King Ruby grapevines against downy mildew and improves its growth, yield, and berries quality

Downy mildew, caused by Plasmopara viticola (Berk. and M. A. Curtis) Berl. and De Toni, is a serious disease of grapevines in general and King Ruby seedless cultivar in particular, affecting their growth and yield. Magnesium carbonate (MgCO₃) is an antitranspirant, which induces stomatal closing and enhances plant growth and physiology. In this study, effect of foliar application of MgCO₃ at 1 and 3% on plant resistance, growth, yield and physiology of grapevines (cv. King Ruby seedless) infected with downy mildew was investigated under field conditions. The obtained results showed that foliar application of MgCO₃ at 3% led to upregulation of the transcription factor JERF3 (9.6-fold), and the defense-related genes GLU (6.3-fold), POD (8.7-fold), PR1 (9.6-fold), and CHI II (8.6-fold). In addition, this treatment led to a reduction in the disease severity (78%), and an increment in the yield per grapevine (20%). Furthermore, biochemical properties of berries, total contents of the photosynthetic pigments, phenolic compounds, and activities of the antioxidant enzymes peroxidase and polyphenol oxidase also enhanced. In contrast, lipid peroxidation, and H₂O₂ content in grapevines leaves reduced in response to MgCO₃ spraying. Light microscope observations revealed that average number of closed stomata increased and the average stomatal pore area decreased in grapevines leaves as a result to MgCO₃ spraying. Based on these results, we can conclude that spraying with MgCO₃ at 3% has effective roles in inducing the plant resistance against downy mildew, and improving the growth and yield of grapevines.