In vivo Antiphytoviral Activity of Essential Oils and Hydrosols From Origanum vulgare, Thymus vulgaris, and Rosmarinus officinalis to Control Zucchini Yellow Mosaic Virus and Tomato Leaf Curl New Delhi Virus in Cucurbita pepo L.

In the last decades, the interest in biological activity of natural compounds has been growing. In plant protection, essential oils have been reported to exhibit antiviral, antimycotic, and antiparasitic activities, and are regarded as promising for the formulation of safe antimicrobial agents. Attention has also been focused on hydrosols, the by-products of hydro-distillation of essential oils. Their production is easy, fast, and cheap, and they seem to arise less concern for human health than essential oils. Plant viruses represent a major concern for agricultural crops since no treatment compound is available for virus control. This work was aimed at evaluating the antiphytoviral effectiveness of treatments with three essential oils and corresponding hydrosols extracted from Origanum vulgare, Thymus vulgaris, and Rosmarinus officinalis on Cucurbita pepo plants infected by zucchini yellow mosaic virus or tomato leaf curl New Delhi virus. Treatments were applied either concurrently or after virus inoculation to ascertain an inhibition or curative activity, respectively. Symptoms were observed and samplings were performed weekly. Virus titer and expression levels of phenylalanine ammonia lyase gene (PAL) were measured on treated and untreated infected plants by real-time PCR. PAL gene plays an important role in plant defense response as it is involved in tolerance/resistance to phytopathogens. Results indicated that treatments were effective against tomato leaf curl New Delhi virus whether applied simultaneously with the inoculation or after. A major inhibition was observed with O. vulgare essential oil and hydrosol, resulting in 10-4-fold decrease of virus titer 3 weeks after treatment. Curative activity gave maximum results with all three essential oils and T. vulgaris and R. officinalis hydrosols, recording from 10-2-fold decrease to virus not detected 4 weeks after treatment. An induction of PAL gene expression was recorded at 12 d.p.i. and then was restored to the levels of untreated control. This allows to hypothesize an early plant defense response to virus infection, possibly boosted by treatments. Plant extracts' composition was characterized by gas chromatography-mass spectrometry. Phenols were largely main components of O. vulgare and T. vulgaris extracts (carvacrol and thymol, respectively), while extracts from R. officinalis were based on monoterpene hydrocarbons (essential oil) and oxygenated monoterpenes (hydrosol).

Metabolites response to onion yellow dwarf virus (OYDV) infection in 'Rossa di Tropea' onion during storage: a 1 H HR-MAS NMR study.

BACKGROUND: Plant viral infections induce changes in metabolic components in the host plant, with potential effects on compositional, organoleptic and storability features of agricultural products. Identification of modulated metabolites may provide clues concerning pathways implementing responses in plant-pathogen interactions. A time course study of metabolic fingerprinting of onion yellow dwarf virus (OYDV)-infected versus healthy 'Rossa di Tropea' onion bulbs was performed using proton high-resolution magic angle spinning nuclear magnetic resonance (1 H HR-MAS NMR) and ultra-performance liquid chromatography (UPLC), providing an overview of the metabolic state of the bulb in response to OYDV infection during storage. RESULTS: Metabolites accumulated/depleted upon infection were identified, belonging to flavonoid, saccharide, amino acid and organic acid classes. A decrease in quercetin glucosides content and antioxidant activity was observed in infected bulbs; some amino acids (Arg, Asn, Phe, Val) accumulated, while others were depleted (Leu); for some metabolites, a bimodal time-course was observed during storage (Glc, Lys). Virus interference on metabolic pathways, and the effects of the metabolic shift on edible product storability, organoleptic and nutritional quality were discussed. CONCLUSIONS: OYDV infection induces a metabolic shift in 'Rossa di Tropea' onion during bulb storage, involving several pathways and affecting storability and organoleptic and nutritional quality of bulbs at marketable stage. © 2020 Society of Chemical Industry.

Development of a reverse transcription-loop- mediated isothermal amplification (LAMP) assay for the rapid detection of onion yellow dwarf virus.

Onion yellow dwarf virus (OYDV) is one of the most important viral pathogens of onion. In particular, on 'Rossa di Tropea' onion, granted with Protected Geographical Indication (PGI) trademarks, this pathogen represents the most limiting biotic stress in terms of spread, severity of symptoms and damage, and its detection is necessary to preserve high quality standards and avoid yield losses. A reverse transcription-loop mediated isothermal amplification (RT-LAMP) assay was developed for detection of OYDV. The specificity, sensitivity, repeatability and reproducibility of the assay were validated according to EPPO standard PM7/98 (2). Diagnostic specificity, diagnostic sensitivity and diagnostic accuracy were determined in both leaf and bulb tissues. To enhance the feasibility of a LAMP-based method for field diagnosis, several nucleic acid extraction methods were compared to simplify sample preparation. The results showed the reliability of the method for OYDV detection, with a limit of detection (LOD) comparable to real time reverse transcription polymerase chain reaction (RT-qPCR). The ease of sample preparation, and the more than acceptable LOD, indicated that the RT-LAMP assay could be used in plant pathology laboratories with limited facilities and resources, as well as directly in the field. This work was carried out in the frame of "SI.ORTO" project.