Alnus glutinosa and Orientus ishidae (Matsumura, 1902) share phytoplasma genotypes linked to the ‘Flavescence dorée’ epidemics

Abstract

| INTRODUC TI ON'Flavescence dorée' (FD), a quarantine grapevine disease caused by FD phytoplasmas (FDp), was first reported in the 1950s in south-western France (Caudwell, 1957). The spread of FD to an epidemic level within vineyards is caused by the Nearctic leafhopper Scaphoideus titanus (Ball, 1932), which, in Europe, usually accomplishes its whole life cycle on plants of the genus Vitis

Gone‐wild grapevines in forests may act as a potential habitat for ‘Flavescence dorée’ phytoplasma vectors and inoculum

“…Consequently, they may well have an epidemiological impact, considering the possible migration to the cultivated compartment (Lessio et al, 2014). The concomitant presence of O. ishidae may reinforce this role in the maintenance or triggering of the FD epidemics, especially in combination with alternative FDp host plant species such as Alnus glutinosa , on which infection rates up to 85% were found for O. ishidae (Rizzoli et al, 2021). The co‐habitation of GWGVs and other plant species known to be potentially infected with FDp genotypes compatible with S. titanus and O. ishidae represents an additional risk factor for the FD epidemics (Malembic‐Maher et al, 2020; Rizzoli et al, 2021).…”

“…The concomitant presence of O. ishidae may reinforce this role in the maintenance or triggering of the FD epidemics, especially in combination with alternative FDp host plant species such as Alnus glutinosa , on which infection rates up to 85% were found for O. ishidae (Rizzoli et al, 2021). The co‐habitation of GWGVs and other plant species known to be potentially infected with FDp genotypes compatible with S. titanus and O. ishidae represents an additional risk factor for the FD epidemics (Malembic‐Maher et al, 2020; Rizzoli et al, 2021). The same may be true for other alternative FDp epidemiological cycles, such as the association of Dictyophara europaea (Linnaeus, 1767) with Clematis vitalba (Filippin et al, 2009), although, contrarily to O. ishidae , D. europaea has never been found to be able to lay eggs on grapevine (Krstić et al, 2016).…”

“…All the detected GWGV sites were described in terms of covered area, mean slope, distance from the nearest cultivated vineyard, forest type (including the presence of spontaneous plant species, such as A. glutinosa , C. avellana , etc., which may host FDp inoculum and/or alternative FDp vectors, such as O. ishidae [Mehle et al, 2019; Rizzoli et al, 2021]), last time of registration as vineyard on official topographic maps (hereinafter referred to as ‘Last_T’), and presence of GWGVs showing symptoms linked to Grapevine Yellows (GYs) (EPPO/CABI, 1997). For the detected GWGVs which were not indicated on the map intersections, aerial images were checked to confirm the presence of forest since at least 1969 (Swisstopo, 2023), as well as to assess the possible origin of the grapevines.…”

“…More recently, FD hotspots have also been identified in the eastern part of the country, namely, in the Cantons of Vaud, Geneva and Valais (Canton of Valais, 2022; Schaerer et al, 2007). The lack of success of the mandatory containment and eradication measures and the related spread of the FD epidemics have been mainly attributed to (i) the use of uncertified propagation material which was not treated with hot water, which may cause the introduction of FDp‐infected grapevines into previously FDp‐free locations (Caudwell, 1990; Caudwell et al, 1997), (ii) the inability to ensure the systematic eradication of FDp‐infected grapevines (Jeger et al, 2016), (iii) the possible role of additional epidemiological cycles induced by alternative FDp vectors and host plant species (Jarausch et al, 2021; Malembic‐Maher et al, 2020; Rizzoli et al, 2021) and (iv) the role of abandoned vineyards where S. titanus populations are not controlled and FDp‐infected grapevines are not eradicated (Lessio et al, 2007; Ripamonti et al, 2020). These last two points may be particularly relevant for the traditional vineyard agroecosystem of Southern Switzerland, which consists of small to midsize plots embedded in areas of differing land use, including the forest area.…”

“…Regarding the latter, Wyler et al (2021) calculated that approximately 43.1% (i.e., 440 km) of the overall vineyard perimeters are less than 25 m away from the nearest forest edge. This situation may represent a higher phytosanitary risk for the vineyards due to the proximity of woody species such as Alnus glutinosa and Corylus avellana , which are the most important host plants for the best alternative FDp vector candidate, Orientus ishidae (Matsumura, 1902) and, especially in the case of A. glutinosa , an FDp inoculum reservoir in the landscape compartment of Southern Switzerland (Casati et al, 2017; Mehle et al, 2019; Rizzoli et al, 2021). Furthermore, a minor role by putative vectors such as the Nearctic leafhoppers Japananus hyalinus (Osborn, 1900), Graphocephala fennahi (Young, 1977) and Hishimonus hamatus (Kuoh, 1976) cannot be excluded, as these species were already found harbouring FDp genotypes compatible with S. titanus and grapevine in Southern Switzerland (Belgeri et al, 2021).…”