Silica Nanoparticles as a Probable Anti-Oomycete Compound Against Downy Mildew, and Yield and Quality Enhancer in Grapevines: Field Evaluation, Molecular, Physiological, Ultrastructural, and Toxicity Investigations.

Younes M Rashad,Hany H A El-Sharkawy,Doaa A Galilah,Elsayed S Abdel Razik,Bassam E A Belal

doi:10.3389/fpls.2021.763365

Abstract

Downy mildew is the most destructive disease of grapevines in the regions of relatively warm and humid climate causing up to 50% yield losses. Application of silicon- (Si-) based products have been extensively studied against various oomycete, fungal, bacterial, and viral plant diseases, but studies on Si application in their nanosize are limited. In this study, the field application of silica nanoparticles (SiNPs) on Thompson Seedless grapevines (H4 strain) infected with downy mildew was evaluated. In addition, molecular, physiological, ultrastructural, and toxicity investigations were also conducted. The obtained results revealed that spraying of grapevines with SiNPs at 150 ppm significantly overexpressed the transcription factor jasmonate and ethylene-responsive factor 3 recording 8.7-fold, and the defense-related genes β-1,3-glucanase (11-fold), peroxidase (10.7-fold) pathogenesis-related-protein 1 (10.6-fold), and chitinase (6.5-fold). Moreover, a reduction up to 81.5% in the disease severity was achieved in response to this treatment. Shoot length and yield per grapevine were considerably enhanced recording up to 26.3 and 23.7% increase, respectively. The berries quality was also improved. Furthermore, this treatment led to an enhancement in the photosynthetic pigments, induction of phenolic and ascorbic acid contents, an increase in the activity of peroxidase and polyphenol oxidase enzymes, and a reduction in the cellular electrolyte leakage, lipid peroxidation, and H2O2 content. Scanning electron microscopy observations showed an increase up to 86.6% in the number of closed stomata and a reduction up to 55% in the average stomatal pore area in response to this treatment. Observations of the transmission electron microscopy showed ultrastructural alterations in the cells of a grapevine leaf due to the infection with downy mildew, including plasmolysis and disruption of the cellular components, abnormal chloroplasts, and thickening of the cell wall and cell membrane. These abnormal alterations were reduced in response to SiNPs spray. In contrast, this study also showed that this treatment had considerable cytotoxic and genotoxic effects at this direct dose/concentration. So, additional investigations to determine the SiNPs residue in the produced edible plant parts are urgently needed. In addition, the pre-harvest interval, toxicity index, and risk assessment should be evaluated before any recommendation for use.

Highlights

Grapevine (Vitis vinifera L.) is one of the most important commercial fruit crops grown worldwide for its edible berries, fresh or dry, or for the production of wine and juice
The inducing effect was due to a gradual elevation of both treatments over time after the first spray, except for silica nanoparticles (SiNPs) treatment at 100 ppm, where the gene expression reached its maximum level at 3 dps2 and declined at 7 dps2
At 3 dps1, downregulation was observed in response to spraying with SiNPs at 100 ppm, while no change in the gene expression was recorded for the SiNPs treatment at 150 ppm in comparison with the unsprayedinfected grapevines

Summary

Introduction

Grapevine (Vitis vinifera L.) is one of the most important commercial fruit crops grown worldwide for its edible berries, fresh or dry (raisins), or for the production of wine and juice. Thompson seedless grapevine (H4 strain) has received extensive attention in the recent few years due to its characteristic yield production, but the problem of this cultivar is its high susceptibility to infection with downy mildew. De Toni, is the most destructive disease of grapevines in the regions of relatively warm and humid climate. This obligate biotrophic oomycete (family: Peronosporaceae) attacks grapevines and severely reduces their growth and yield causing up to 50% losses (Gessler et al, 2011). Copper-based anti-oomycete fungicides and other synthetic agrochemicals, such as fosetyl-aluminum, metalaxyl, and mandipropamid are available and still commonly used today for the control of downy mildew disease, but the improper and frequent use of these anti-oomycete fungicides led to evolution of the pathogen resistance to many anti-oomycete fungicides (Massi et al, 2021). The demand for new antioomycete fungicides is highly increased to overcome the risk of the recently appeared fungicide resistance in the downy mildew pathogen

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