Candidatus Phytoplasma ulmi (elm yellows).

Elm yellows develops in sporadic epidemics after introduction of 'Ca. Phytoplasma ulmi' to areas where vectors are abundant.

Widespread occurrence of 'Candidatus Phytoplasma ulmi' in elm species in Germany

Background: Candidatus Phytoplasma ulmi' is the agent associated with elm yellows and has been categorised in the European Union as a quarantine pathogen. For central and northern European countries, information on the occurrence and distribution of the pathogen and its impact on elms is scarce, so a survey of native elm trees has been conducted in Germany. Results: About 6,500 samples from Ulmus minor , Ulmus laevis and Ulmus glabra , were collected nationwide. Phytoplasma detection was performed by applying a universal 16Sr DNA-based quantitative PCR (qPCR) assay and a novel ' Ca. P. ulmi' specific qPCR assay targeting the 16S-23S spacer region. Both assays revealed that 28% of the samples were infected by ‘ Ca. P. ulmi’, but infection rates of the elm species and regional incidences differed. The phytoplasma presence in the trees was not correlated to disease-specific symptoms. The survey identified a regional disparity of infection which was high in east, south and central Germany, whereas only a few infected sites were found in the western and northern parts of the country. Monitoring the seasonal titre of ‘Ca. P. ulmi’ in an infected tree by qPCR revealed a high colonisation in all parts of the tree throughout the year. Conclusions: ‘ Ca. P. ulmi’ is widely present in elms in Germany. The rare occurrence of symptoms indicates either a high degree of tolerance in elm populations or a low virulence of pathogen strains enabling high infection rates in a long-living host.

Widespread occurrence of Candidatus Phytoplasma ulmi infecting elm species in Germany

Background: Candidatus Phytoplasma ulmi is the causative agent of elm yellows and has been categorised in the European Union as a quarantine pathogen in the past. For central and northern European countries, information on the occurrence and distribution of the pathogen and its impact on elms is scarce, so a survey of native elm trees has been conducted in Germany. Results: About 6,500 samples in total, from Ulmus minor , Ulmus laevis and Ulmus glabra , were collected nationwide. Phytoplasma detection was performed by applying a universal 16Sr DNA-based real-time PCR assay and a novel Ca . P. ulmi species-specific real-time PCR assay targeting the 16S-23S spacer region. Both assays revealed that 28% of the samples were infected by Ca . P. ulmi, but infection rates of the elm species and regional incidences differed. The infection of trees is not correlated to disease-specific symptoms. The survey identified a regional disparity of infection which was high in east, south and central Germany, whereas only a few infected sites were found in the western and northern parts of the country. No correlation was apparent between altitude level and the prevalence of infection. First insights into the monitoring of the seasonal titre of Ca . P. ulmi in an infected tree by real-time PCR revealed high colonisation in all parts of the tree throughout the year. Conclusions: Ca . P. ulmi-infection is widely present in elms in Germany. The rare occurrence of symptoms indicates either a high degree of tolerance in elm populations or a low virulence of pathogen strains enabling high infection rates in a long-living host.

Molecular Diversity of Phytoplasmas Associated with Grapevine Yellows Disease in North-Eastern Italy

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.

Grapevine flavescence dorée phytoplasma. [Distribution map].

A new distribution map is provided for Grapevine flavescence dorée phytoplasma [Phytoplasma vitis]. Acholeplasmatales: Acholeplasmataceae: Candidatus Phytoplasma: 16SrV (Elm yellows group). Host: grapevine (Vitis spp.). Information is given on the geographical distribution in Europe (Austria, Croatia, France, Corsica, Mainland France, Hungary, Italy, Portugal, Serbia, Slovenia, Spain, Switzerland).