Abstract
The Eurasian grapevine (Vitis vinifera), an Old World species now cultivated worldwide for high-quality wine production, is extremely susceptible to the agent of downy mildew, Plasmopara viticola. The cultivation of resistant V. vinifera varieties would be a sustainable way to reduce the damage caused by the pathogen and the impact of disease management, which involves the economic, health and environmental costs of frequent fungicide application. We report the finding of unique downy mildew resistance traits in a winemaking cultivar from the domestication center of V. vinifera, and characterize the expression of a range of genes associated with the resistance mechanism. Based on comparative experimental inoculations, confocal microscopy and transcriptomics analyses, our study shows that V. vinifera cv. Mgaloblishvili, native to Georgia (South Caucasus), exhibits unique resistance traits against P. viticola. Its defense response, leading to a limitation of P. viticola growth and sporulation, is determined by the overexpression of genes related to pathogen recognition, the ethylene signaling pathway, synthesis of antimicrobial compounds and enzymes, and the development of structural barriers. The unique resistant traits found in Mgaloblishvili highlight the presence of a rare defense system in V. vinifera against P. viticola which promises fresh opportunities for grapevine genetic improvement.
Highlights
The Eurasian grapevine (Vitis vinifera), an Old World species cultivated worldwide for high-quality wine production, is extremely susceptible to the agent of downy mildew, Plasmopara viticola
The analyses showed that the colonization of leaf tissues by P. viticola followed an analogous pattern in the two cultivars until two dai: the asexual spores of the pathogen penetrated through the stomatal pore and differentiated the substomatal vesicle (Fig. 1A,E) from which the primary hypha with haustorium originated (Fig. 1B,F)
While P. viticola growth inside the leaf tissues of Pinot noir (Fig. 1G,H) showed the regular pattern described by other authors[5], evident alterations were visible in Mgaloblishvili: P. viticola hyphae were hyper-branched, contorted (Fig. 1C) and ill defined, indicating a loss of integrity of the vegetative structure
Summary
The Eurasian grapevine (Vitis vinifera), an Old World species cultivated worldwide for high-quality wine production, is extremely susceptible to the agent of downy mildew, Plasmopara viticola. The threat posed by this fungal pathogen, combined with the ineffectiveness of agronomic practices in halting its diffusion, makes frequent spraying of fungicides unavoidable in areas experiencing high disease pressure This contributes to the status of viticulture as the agricultural activity which makes the most intensive use of plant protection products (http://ec.europa.eu/eurostat/en/web/ products-statistical-books/-/KS-76-06-669). This leads to negative impacts on farmers’ economic situations, human health and the environment, and to a potential reduction of future disease control due to the development of fungicide resistance[3]. Comparative experimental inoculations, confocal microscopy and transcriptomics analyses allowed the description of a rare defense system against P. viticola in winemaking V. vinifera, distinct from that of American Vitis species, opening new perspectives for sustainable viticulture through improved breeding programs
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