Temporal dynamics of grapevine downy mildew in Piwi varieties in San Michele all’Adige Region, Trentino - Italy

ABSTRACT

Downy mildew (Plasmopara viticola), a biotrophic oomycete, is the causal agent of the main disease of the grapevine. The objective of this study was to evaluate the response of nine Piwi varieties (from the German word: “Pilzwiderstandsfähige” = “Disease-resistant”) showing constitutive resistance to downy mildew (P. viticola) and a Vitis vinifera variety (susceptible) as control in an experimental vineyard of Fundazione Edmund Mach (FEM), located in San Michele All’Adige, in the Trentino region of Italy. The vineyard has been conducted for ten years without any chemical treatment and was evaluated in the 2017 crop season. The different varieties were evaluated for downy mildew intensity in the field and stomatal density in the Phytopathology Laboratory of FEM. To evaluate stomatal density, ten leaves of each genotype were collected in the phenological stage véraison, immediately taken to the laboratory and prepared for observation through a magnifying glass (40x), according to Boso et al. (2). In the field trial, mildew incidence and severity assessments were carried out weekly from the beginning of the first symptoms/signs and the epidemics were compared in relation to: a) beginning of symptom/sign appearance (BSA); b) time to reach maximum disease incidence and severity (TRMDI and TRMDS); c) maximum value of disease incidence and severity (Imax and Smax), and d) area under the disease incidence and severity progress curve (AUIDPC and AUSDPC). Piwi varieties presented a mean reduction of 93.9% in mildew severity in relation to the vine variety ‘Pinot Grigio’. The varieties ‘Jasmine’, ‘Muscaris’ and ‘Regent’ showed the lowest intensity of downy mildew infection in the field in the 2017 harvest under the edaphoclimatic conditions of Trentino, Italy. There was a positive relationship between the lowest stomatal density per leaf area and the greatest resistance to P. viticola in the field. Piwi varieties appear as a cultivation option with the aim of reducing the use of pesticides and as sustainable support for the Trentino wine industry.

Keywords
stomatal density; resistant varieties; Trentino viticulture