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Downy mildew is a major threat to viticulture, leading to severe yield loss. The use of traditional copper-based fungicides is effective, but has adverse effects on the environment and human health, making it urgent to develop an environmentally friendly disease management program. Multi-functional kaolin particle film (KPF) is promising as an effective and safer treatment strategy, since this material lacks chemically active ingredients. In this study, ability of Kaolin particle film (KPF) pretreatment to protect grapevine leaves from Plasmopara viticola was tested and the mode of action of KPF was analyzed. KPF application reduced the disease severity and the development of intercellular hyphae. Additionally, there was reduced accumulation of H2O2 and malondialdehyde (MDA) with pretreatment. The observation of ultrastructure on the leaf surface showed KPF deposition and stomatal obstruction, indicating that KPF protected plants against disease by preventing the adhesion of pathogens to the leaf surface and blocking invasion through the stomata. KPF pretreatment also activated host defense responses, as evidenced by increased activities of anti-oxidative enzymes [superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)] and defense-related enzymes [phenylalanine ammonia-lyase (PAL), chitinases, and β-1,3-glucanases], increased phytohormone signals [abscisic acid (ABA), salicylic acid (SA), and jasmonic acid (JA)] and the up-regulation of defense genes related to plant defense. Overall, these results demonstrate that KPF treatment counters grapevine downy mildew by protecting leaves and enhancing plant defense responses.

Summary Glyoxalase I (GLYI) is part of the glyoxalase system; its major function is the detoxification of α‐ketoaldehydes, including the potent and cytotoxic methylglyoxal (MG). Methylglyoxal disrupts mitochondrial respiration and increases production of reactive oxygen species (ROS), which also increase during pathogen infection of plant tissues; however, there have been few studies relating the glyoxalase system to the plant pathogen response. We used the promoter of VvGLYI‐4 to screen the upstream transcription factors and report a NAC (NAM/ATAF/CUC) domain‐containing transcription factor VvNAC72 in grapevine, which is localized to the nucleus. Our results show that VvNAC72 expression is induced by downy mildew, Plasmopara viticola, while the transcript level of VvGLYI‐4 decreases. Further analysis revealed that VvNAC72 can bind directly to the promoter region of VvGLYI‐4 via the CACGTG element, leading to inhibition of VvGLYI‐4 transcription. Stable overexpression of VvNAC72 in grapevine and tobacco showed a decreased expression level of VvGLYI‐4 and increased content of MG and ROS, as well as stronger resistance to pathogen stress. Taken together, these results demonstrate that grapevine VvNAC72 negatively modulates detoxification of MG through repression of VvGLYI‐4, and finally enhances resistance to downy mildew, at least in part, via the modulation of MG‐associated ROS homeostasis through a salicylic acid‐mediated defense pathway.

No abstract

Background and Aims: Grapevine downy mildew, the most destructive grapevine disease caused by Plasmopara viticola, requires more environmentally friendly control measures. A chemically inert kaolin particle film (KPF) was tested for the control of downy mildew. Methods and Results: Grapevines were pretreated with KPF before P. viticola infection under field conditions, then an epidemic was monitored for 2 years (2020 and 2021). A 6% KPF pretreatment significantly delayed the epidemic onset by 1-2 weeks and decreased the disease index by 30% compared to the untreated vines. The concentration of hydrogen peroxide and malondialdehyde in leaves was reduced by the KPF treatment, indicating mitigation of the oxidative damage caused by P. viticola infection. The protective effect of the application of KPF may be due to the increased activity of antioxidant enzymes and antioxidant metabolites. The activity of disease resistance enzymes and the expression of related genes were also increased by KPF treatment. Conclusions: Kaolin particle film reduced grapevine downy mildew and reinforced the defence response of grapevines cultivated in the field. Significance of the Study: The positive effect of KPF against downy mildew for grapevines in the field indicated that there is potential to develop KPF for the control of downy mildew.