Kaolin triggers defense-responsive genes in grapevines (cv. King Ruby seedless) to downy mildew and enhances its vegetative development, production, and berries quality standards

Abstract

Plasmopara viticola, the causative of downy mildew, is one of the most destructive pathogens that attack grapevines worldwide. Despite to its high productivity and good berries quality, King Ruby seedless grapevines are highly susceptible to P. viticola and suffer its adverse effects. In this study, kaolin spraying at 1 and 3% was investigated under field conditions as a likely anti-oomycete substance. Results from the field experiment showed that kaolin spraying at 3% resulted in a considerable reduction in the infection severity (80.1%). Overexpression of the responsive factor JERF3 (4-fold), and the defense-responsive genes PR1 (4.2-fold), CHI II (3.9-fold), POD (2.7-fold), and GLU (2.8-fold) was recorded. Furthermore, a promotion in the phenolic compounds in plant roots (106.5%), as well as activities of peroxidase (182.5%) and polyphenol oxidase (136.4%) enzymes was also recorded in response to this treatment. A decrease in lipid peroxidation, H2O2 content, and the cellular electrolyte leakage, as well as an increment in ascorbic acid content in grapevine leaves were observed. Scanning electron microscopy showed that kaolin treatment at 3% induced stomatal closure and led to a reduction in the stomatal area in grapevines leaves. Transmission electron microscopy indicated abnormal variations in the ultrastructure of the infected mesophyll cells of grapevine leaf. This abnormality decreased due to kaolin application at 3%. Moreover, kaolin spraying resulted in a significant enhancement in most of the evaluated growth parameters. Yield per grapevine was also improved (18.5%), as well as all evaluated berries quality standards in response to kaolin application. It can be concluded that kaolin application at 3% is a promising protective solution to control downy mildew and improve the grapevines growth and production.