Kaolin Particle Film Protects Grapevine cv. Cabernet Sauvignon Against Downy Mildew by Forming Particle Film at the Leaf Surface, Directly Acting on Sporangia and Inducing the Defense of the Plant

Abstract

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.

Kaolin particle film limits grapevine downy mildew epidemic under open‐field conditions and stimulates the plant defence response

“…Enhanced resistance due to KPF was demonstrated by enhanced defence‐promoting metabolite and gene expression in both years, and was consistent with our previous results on isolated leaf discs (Wang et al 2022), indicating the enhancement of host defence response by KPF could also be achieved under field conditions. The magnitude of the KPF increases, however, was not consistent in the 2 years.…”

“…In this study, the activity of PR4, PR2 and PAL was increased in KPF treatments. These results support a positive role of KPF in the induction of grapevine resistance under open‐field conditions, consistent with its previously demonstrated effectiveness in detached leaves (Wang et al 2022).…”

“…As a valuable multifunctional new tool, the ability of KPF to reduce P. viticola infection by forming a particle film at the leaf surface, directly acting on sporangia, and inducing the defence of the vine was demonstrated in our previous study (Wang et al 2022). To directly replace conventional fungicides, however, with KPF in vineyards, the effect of KPF on severity and on temporal dynamics of grapevine downy mildew under field conditions needs to be evaluated.…”

“…These results indicated that the conditions required for primary infection, such as sufficient amounts of pathogen and water, are less ideal for KPFtreated leaves (Burruano 2000, Gessler et al 2011. This is because the KPF treatment interferes with the direct contact of leaves with pathogens and water by kaolin deposition on the leaf surface, as demonstrated previously (Wang et al 2022). The severity of grape downy mildew infection is closely related to climatic conditions, among which temperature, humidity and rainfall are the most important (Gessler et al 2011).…”

“…The previous study demonstrated a reduction in the incidence of downy mildew by KPF treatment (Wang et al 2022). The residue of KPF reduces zoospore release, prevents P. viticola infection and development, and stimulates host resistance.…”