Publications

4364

AbstractThe fast development of molecular taxonomy is impacting our knowledge of the world parasite diversity at an unprecedented level. A number of operational taxonomic units have been uncovered and new species described. However, it is not always that new parasite species are being described in compliance with the International Code of Zoological Nomenclature. This is the case of “Candidatus Dirofilaria hongkongensis”, a nematode found in dogs, jackals and humans in Hong Kong and parts of India. This name has been proposed without a formal description and without the designation of a holotype, and therefore is an unavailable name. Finally, we argue that using the provisional status Candidatus in zoological nomenclature is inappropriate, considering this term is not considered in the International Code of Zoological Nomenclature.

Abstract 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 6500 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.

Phytoplasmas have been associated with a disease that affects trees of at least 11 species from different botanic families in Bogotá, Colombia. ‘Candidatus Phytoplasma asteris’ and ‘Candidatus Phytoplasma fraxini’ are the major groups of phytoplasma in the area of Bogotá. In this study, the genetic diversity within ‘Ca. P. asteris’ and ‘Ca. P. fraxini’ was studied in five urban tree species: Croton species (Euphorbiaceae), Fraxinus uhdei (Oleaceae), Magnolia grandiflora (Magnoliaceae), Populus nigra (Salicaceae) and Quercus humboldtii (Fagaceae). Analyses of the 16S rRNA gene using nested PCR, RFLP and sequencing showed that phytoplasmas of ‘Ca. P. asteris’ could be assigned to: subgroup 16SrI-B; a new subgroup named 16SrI-AF, with a restriction pattern similar to that of 16SrI-B; and a new subgroup named 16SrI-AG, with a restriction pattern similar to that of 16SrI-K and 16SrI-AH with a restriction pattern similar to that of 16SrI-AC. ‘Ca. P. fraxini’ isolates belonged to a new subgroup named 16SrVII-G, with a restriction pattern similar to that of 16SrVII-A. To complement the identification of the phytoplasma strains, we amplified nonribosomal genes such as leuS and secA. Unexpectedly, it was observed that in 16 trees in which 16S rRNA gene analysis showed the presence of ‘Ca. P. fraxini’ only, the leuS or secA primers amplified sequences exclusively affiliated to ‘Ca. P. asteris. In those plants, sequences belonging to ‘Ca. P. fraxini’ leuS or secA genes were not amplified. The present work contributes to the identification of novel strains of both species in Colombia, and supports previous suggestions that phytoplasmas in South America are highly variable.

Specific scopeThis Standard describes a national regulatory control system for the bacterial pathogen ‘Candidatus Liberibacter solanacearum’ and its vector Bactericera cockerelli when regulated as quarantine pests. It also covers measures to reduce the risk of ‘Ca. L. solanacearum’ spreading to potato production systems when listed as a regulated nonquarantine pest (RNQP) on seed potatoFor the EPPO A1 listed pests recommended for regulation as quarantine pests B. cockerelli and ‘Ca. L. solanacearum’ (Solanaceae haplotypes, i.e. non‐European haplotypes, such as haplotypes A and B), the Standard describes measures to achieve: Exclusion from the EPPO region of B. cockerelli, which is an efficient vector of ‘Ca. L. solanacearum’ within solanaceous crops (e.g. potato, tomato) Eradication of incursions of B. cockerelli Exclusion from the EPPO region of non‐European haplotypes of ‘Ca. L. solanacearum’ Eradication of incursions of non‐European haplotypes of ‘Ca. L. solanacearum’. Although reference will only be made to the non‐European haplotypes A and B, the Standard would also apply to new non‐European haplotypes of ‘Ca. L. solanacearum’ which may have different host ranges or which may be vectored more efficiently by psyllids which are widespread in the region.For the haplotypes which are not recommended for regulation as quarantine pests but are recommended for regulation as RNQPs on seed potato (i.e. European haplotypes, such as C, D and E), the Standard describes measures (specified in Appendix 4) to reduce the risk of spread to potato production systems to achieve: Exclusion of European haplotypes of ‘Ca. L. solanacearum’ from the potato production system Suppression of European haplotypes of ‘Ca. L. solanacearum’ in potato production systems where they are present. Although reference will only be made to haplotypes C, D and E, Appendix 4 would also apply to new European haplotypes of ‘Ca. L. solanacearum’.SpecificapprovalFirst approved in 2017‐09. Revised in 2020‐09.