Abstract
A 3-year survey was conducted in Northern Italy to verify the presence and diversity of phytoplasmas in selected vineyards showing symptoms of severe yellows. Symptomatic and asymptomatic grapevines were sampled, and insects were collected using yellow sticky traps. The phytoplasmas detected in grapevine samples were different according to the years: "flavescence dorée" (16SrV-C/D) was detected together with other phytoplasmas such as 16SrXII-A ('Candidatus Phytoplasma solani'-related, bois noir), 16SrI-B ('Ca. P. asteris'-related, aster yellows), 16SrX-B ('Ca. P. prunorum'-related, European stone fruit yellows), and 16SrV-A ('Ca. P. ulmi'-related, elm yellows). Moreover, phytoplasmas belonging to 16SrVII-A ('Ca. P. fraxini'-related) and 16SrVI ('Ca. P. trifolii'-related) subgroups were also identified. Identification of phytoplasmas was also carried out from insects and showed the presence of some of these phytoplasmas in Scaphoideus titanus and Orientus ishidae: 16SrXII-A, 16SrVII, and 16SrVI phytoplasmas were detected in specimens of both species, while 16SrXII-A and 16SrI-B phytoplasma strains were identified in Orientus ishidae and Hyalesthes obsoletus, and 16SrX-B in S. titanus. Direct sequencing of selected amplicons obtained from 16S rRNA, rp, and tuf genes from grapevine and insect samples confirmed the phytoplasma identification. The 16SrVII-A and 16SrVI phytoplasmas were never detected before in grapevine, S. titanus and Orientus ishidae in Europe and their epidemiological importance is being monitored.
Highlights
A 3-year survey was conducted in Northern Italy to verify the presence and diversity of phytoplasmas in selected vineyards showing symptoms of severe yellows
The phytoplasmas detected in grapevine samples were different according to the years: “flavescence dorée” (16SrV-C/D) was detected together with other phytoplasmas such as 16SrXII-A (‘Candidatus Phytoplasma solani’related, bois noir), 16SrI-B (‘Ca. P. asteris’-related, aster yellows), 16SrX-B
Identification of phytoplasmas was carried out from insects and showed the presence of some of these phytoplasmas in Scaphoideus titanus and Orientus ishidae: 16SrXII-A, 16SrVII, and 16SrVI phytoplasmas were detected in specimens of both species, while 16SrXII-A and 16SrI-B phytoplasma strains were identified in Orientus ishidae and Hyalesthes obsoletus, and 16SrX-B in S. titanus
Summary
A 3-year survey was conducted in Northern Italy to verify the presence and diversity of phytoplasmas in selected vineyards showing symptoms of severe yellows. Phytoplasmas are biotrophic plant-pathogenic wall-less prokaryotes belonging to the class mollicutes with a low G+C content, closely related to Gram-positive bacteria They are phloem-limited and mainly transmitted by insects belonging to leafhopper (Cicadellidae), planthopper (Cixiidae), or psyllid (Psyllidae) families (Weintraub and Beanland 2006). The main yellows diseases in grapevine in Europe are “flavescence dorée” (FD, 16SrV-C/D ribosomal subgroups) (Bertaccini et al 1995; Martini et al 1999) and bois noir (BN, ‘Candidatus Phytoplasma solani’, 16SrXII-A ribosomal subgroup) (Quaglino et al 2013), transmitted by the monovoltive ampelophagous leafhopper Scaphoideus titanus Ball and by the polyphagous cixiid Hyalestes obsoletus Signoret, respectively (Schvester et al 1961; Sforza et al 1998). More recently in Europe, 16SrV-C phytoplasmas linked to FD presence in grapevine were detected in different weed species such as Clematis vitalba, Alnus glutinosa, Sambucus nigra, Cornus sanguinosa, Prunus spinosa, Ulmus glabra, Ulmus minor, Ulmus spp., Corylus avellane, and Salix sp. (Angelini et al 2004; Casati et al 2017; Filippin et al.2005, 2009; Maixner et al 2000).On the other hand, stolbur-related phytoplasmas
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