Unlocking the vast genomic diversity stored in natural history collections would create unprecedented opportunities for genome-scale evolutionary, phylogenetic, domestication and population genomic studies. Many researchers have been discouraged from using historical specimens in molecular studies because of both generally limited success of DNA extraction and the challenges associated with PCR-amplifying highly degraded DNA. In today's next-generation sequencing (NGS) world, opportunities and prospects for historical DNA have changed dramatically, as most NGS methods are actually designed for taking short fragmented DNA molecules as templates. Here we show that using a standard multiplex and paired-end Illumina sequencing approach, genome-scale sequence data can be generated reliably from dry-preserved plant, fungal and insect specimens collected up to 115 years ago, and with minimal destructive sampling. Using a reference-based assembly approach, we were able to produce the entire nuclear genome of a 43-year-old Arabidopsis thaliana (Brassicaceae) herbarium specimen with high and uniform sequence coverage. Nuclear genome sequences of three fungal specimens of 22–82 years of age (Agaricus bisporus, Laccaria bicolor, Pleurotus ostreatus) were generated with 81.4–97.9% exome coverage. Complete organellar genome sequences were assembled for all specimens. Using de novo assembly we retrieved between 16.2–71.0% of coding sequence regions, and hence remain somewhat cautious about prospects for de novo genome assembly from historical specimens. Non-target sequence contaminations were observed in 2 of our insect museum specimens. We anticipate that future museum genomics projects will perhaps not generate entire genome sequences in all cases (our specimens contained relatively small and low-complexity genomes), but at least generating vital comparative genomic data for testing (phylo)genetic, demographic and genetic hypotheses, that become increasingly more horizontal. Furthermore, NGS of historical DNA enables recovering crucial genetic information from old type specimens that to date have remained mostly unutilized and, thus, opens up a new frontier for taxonomic research as well.

Tomato brown rugose fruit virus (ToBRFV) is a Tobamovirus that was first observed in 2014 and 2015 on tomato plants in Israel and Jordan respectively. Since the first description, the virus has been reported from all continents except Oceania and Antarctica, and has been found infecting both tomato and pepper crops. In October 2019, the Dutch National Plant Protection Organization received a ToBRFV infected tomato sample as part of a generic survey targeting tomato pests. Presence of the virus was verified using Illumina sequencing. A follow-up survey was initiated to determine the extent of ToBRFV presence in the Dutch tomato horticulture and identify possible linkages between ToBRFV genotypes, companies and epidemiological traits. Nextstrain was used to visualize these potential connections. By November 2019, 68 companies had been visited of which 17 companies were found to be infected. The 50 ToBRFV genomes from these outbreak locations group in three main clusters, which are hypothesized to represent three original sources. No correlation was found between genotypes, companies and epidemiological traits, and the source(s) of the Dutch ToBRFV outbreak remain unknown. This paper describes a Nextstrain build containing ToBRFV genomes up to and including November 2019. Sharing data with this interactive online tool will enable the plant virology field to better understand and communicate the diversity and spread of this new virus. Organizations are invited to share data or materials for inclusion in the Nextstrain build, which can be accessed at https://nextstrain.nrcnvwa.nl/ToBRFV/20191231.

In this study, six methods for the detection of Phytophthora ramorum in planta were compared using naturally infested rhododendron plant material. The methods included two immunological methods, one an enzyme-linked immunosorbent assay (ELISA) and the other using a lateral flow format (LFD). Three molecular tests based on the polymerase chain reaction (PCR) using TaqMan chemistry also were assessed, including two assays designed for specific detection of P. ramorum and one designed for genus-level detection of Phytophthora. Isolation followed by morphological identification also was assessed. The diagnostic values of each of the methods, evaluated based on diagnostic sensitivity, diagnostic specificity, positive predictive value, and negative predictive value, were calculated based upon the test results from 148 field samples. The “gold standard” used for the calculations was the final diagnosis, which was based on either a positive PCR result or successful isolation of P. ramorum. The Phytophthora spp. TaqMan PCR, ELISA, and LFD had higher sensitivities than the P. ramorum-specific methods, which make them useful as prescreening methods, where positive results must be confirmed by PCR or isolation. The article discusses practical advantages and disadvantages of each of the methods and how they are valuable in the diagnostic process, according to the circumstances of use (that is, diagnosis or surveillance) and in relation to the prevalence of P. ramorum infestation in the population to be tested.

Synchytrium endobioticum is an obligate biotrophic soilborne Chytridiomycota (chytrid) species that causes potato wart disease, and represents the most basal lineage among the fungal plant pathogens. We have chosen a functional genomics approach exploiting knowledge acquired from other fungal taxa and compared this to several saprobic and pathogenic chytrid species. Observations linked to obligate biotrophy, genome plasticity and pathogenicity are reported. Essential purine pathway genes were found uniquely absent in S. endobioticum, suggesting that it relies on scavenging guanine from its host for survival. The small gene-dense and intron-rich chytrid genomes were not protected for genome duplications by repeat-induced point mutation. Both pathogenic chytrids Batrachochytrium dendrobatidis and S. endobioticum contained the largest amounts of repeats, and we identified S. endobioticum specific candidate effectors that are associated with repeat-rich regions. These candidate effectors share a highly conserved motif, and show isolate specific duplications. A reduced set of cell wall degrading enzymes, and LysM protein expansions were found in S. endobioticum, which may prevent triggering plant defense responses. Our study underlines the high diversity in chytrids compared to the well-studied Ascomycota and Basidiomycota, reflects characteristic biological differences between the phyla, and shows commonalities in genomic features among pathogenic fungi.

In Europe, the air-borne accidental introduction of exotic mosquito species (EMS) has been demonstrated using mosquito surveillance schemes at Schiphol International Airport (Amsterdam, The Netherlands). Based upon these findings and given the increasing volume of air transport movements per year, the establishment of EMS after introduction via aircraft is being considered a potential risk. Here we present the airport surveillance results performed by the Centre for Monitoring of Vectors of the Netherlands, by the Monitoring of Exotic Mosquitoes (MEMO) project in Belgium, and by the Public Health England project on invasive mosquito surveillance. The findings of our study demonstrate the aircraft mediated transport of EMS into Europe from a wide range of possible areas in the world. Results show accidental introductions of Aedes aegypti and Ae. albopictus, as well as exotic Anopheles and Mansonia specimens. The findings of Ae. albopictus at Schiphol airport are the first evidence of accidental introduction of the species using this pathway in Europe. Furthermore, our results stress the importance of the use of molecular tools to validate the morphology-based species identifications. We recommend monitoring of EMS at airports with special attention to locations with a high movement of cargo and passengers.

Potato wart disease is considered one of the most important quarantine pests for cultivated potato and is caused by the obligate biotrophic chytrid fungus Synchytrium endobioticum . This review integrates observations from early potato wart research and recent molecular, genetic, and genomic studies of the pathogen and its host potato. Taxonomy, epidemiology, pathology, and formation of new pathotypes are discussed, and a model for molecular S. endobioticum– potato interaction is proposed. Taxonomy: Currently classified as kingdom: Fungi, phylum: Chytridiomycota, class: Chytridiomycetes, order: Chytridiales, family: Synchytriaceae, genus: Synchytrium , species: Synchytrium endobioticum , there is strong molecular support for Synchytriaceae to be transferred to the order Synchytriales. Hosts and disease symptoms: Solanum tuberosum is the main host for S. endobioticum but other solanaceous species have been reported as alternative hosts. It is not known if these alternative hosts play a role in the survival of the pathogen in (borders of) infested fields. Disease symptoms on potato tubers are characterized by the warty cauliflower‐like malformations that are the result of cell enlargement and cell multiplication induced by the pathogen. Meristematic tissue on tubers, stolons, eyes, sprouts, and inflorescences can be infected while the potato root system seems to be immune. Pathotypes: For S. endobioticum over 40 pathotypes, which are defined as groups of isolates with a similar response to a set of differential potato varieties, are described. Pathotypes 1(D1), 2(G1), 6(O1), and 18(T1) are currently regarded to be most widespread. However, with the current differential set other pathogen diversity largely remains undetected. Pathogen–host interaction: A single effector has been described for S. endobioticum (AvrSen1), which is recognized by the potato Sen1 resistance gene product. This is also the first effector that has been described in Chytridiomycota, showing that in this fungal division resistance also fits the gene‐for‐gene concept. Although significant progress was made in the last decade in mapping wart disease resistance loci, not all resistances present in potato breeding germplasm could be identified. The use of resistant varieties plays an essential role in disease management.