SummaryAn analysis of incidence of Phytophthora spp. in 732 European nurseries producing forest transplants, larger specimen trees, landscape plants and ornamentals, plus 2525 areas in which trees and shrubs were planted, is presented based on work conducted by 38 research groups in 23 European countries between 1972 and 2013. Forty-nine Phytophthora taxa were recorded in 670 nurseries (91.5%); within these nurseries, 1614 of 1992 nursery stands (81.0%) were infested, although most affected plants appeared healthy. In forest and landscape plantings, 56 Phytophthora taxa were recovered from 1667 of 2525 tested sites (66.0%). Affected plants frequently showed symptoms such as crown thinning, chlorosis and dieback caused by extensive fine root losses and/or collar rot. Many well-known highly damaging host-Phytophthora combinations were frequently detected but 297 and 407 new Phytophthora-host associations were also observed in nurseries and plantings, respectively. On average, 1.3 Phytophthora species/taxa per infested nursery stand and planting site were isolated. At least 47 of the 68 Phytophthora species/taxa detected in nurseries and plantings were exotic species several of which are considered well established in both nurseries and plantings in Europe. Seven known Phytophthora species/taxa were found for the first For. Path. 46 (2016) 134-163 doi: 10.1111/efp.12239 © 2015 http://wileyonlinelibrary.com/ time in Europe, while 10 taxa had not been previously recorded from nurseries or plantings; in addition, 5 taxa were first detections on woody plant species. Seven Phytophthora taxa were previously unknown to science. The reasons for these failures of plant biosecurity in Europe, implications for forest and semi-natural ecosystems and possible ways to improve biosecurity are discussed.

Cylindrocladium buxicola is a fungal pathogen that causes a severe leaf and twig blight on Buxus spp. Laboratory experiments were carried out to study the in vitro effect of 13 fungicides on mycelial growth and conidia germination of the fungus. Based on the values of the effective concentration at which mycelial growth was inhibited by 50%, the fungicide Stroby (kresoxim-methyl) and the combined fungicides Opponent (epoxiconazole + kresoxim-methyl + pyraclostrobin), Opera (epoxiconazole + pyraclostrobin), and Signum (boscalid + pyraclostrobin) were the most effective at inhibiting mycelial growth and conidia germination. Pathogenicity assays showed that the host range of the fungus was not limited to the genus Buxus because Sarcococca sp. also was susceptible. None of the 10 boxwood species and cultivars tested were immune to the disease, although Buxus balearica as well as Sarcococca sp. showed significantly lower levels of infection as measured by the expression of leaf symptoms and the number of conidia produced on host tissue, the latter probably contributing to the apparent resistance of these species in the field. Microscopic observation showed that disease development was very rapid and aggressive on B. sempervirens ‘Suffruticosa’ where it was able to survive at least 5 years on decomposing fallen leaves.

Most Phytophthora spp. are destructive plant pathogens; therefore, effective monitoring and accurate early detection are important means of preventing potential epidemics and outbreaks of diseases. In the current study, a membrane-based oligonucleotide array was developed that can detect Phytophthora spp. reliably using three DNA regions; namely, the internal transcribed spacer (ITS), the 5' end of cytochrome c oxidase 1 gene (cox1), and the intergenic region between cytochrome c oxidase 2 gene (cox2) and cox1 (cox2-1 spacer). Each sequence data set contained ≈250 sequences representing 98 described and 15 undescribed species of Phytophthora. The array was validated with 143 pure cultures and 35 field samples. Together, nonrejected oligonucleotides from all three markers have the ability to reliably detect 82 described and 8 undescribed Phytophthora spp., including several quarantine or regulated pathogens such as Phytophthora ramorum. Our results showed that a DNA array containing signature oligonucleotides designed from multiple genomic regions provided robustness and redundancy for the detection and differentiation of closely related taxon groups. This array has the potential to be used as a routine diagnostic tool for Phytophthora spp. from complex environmental samples without the need for extensive growth of cultures.

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The pathogenicity of an isolate of a Pythium species from Signy Island in the South Orkney Islands was tested against the Antarctic hairgrass Deschampsia antarctica. The isolate was found to infect plants at 8ºC and to cause foliar and root symptoms similar to those seen in other Pythium infections in grasses. Analysis of ribosomal RNA sequences placed it, together with another isolate from Antarctica, in a clade that included the known snow moulds caused by Pythium spp. Sporangia and oogonia were produced in culture, but the isolate differed from other Pythium spp. in producing chlamydospores in older cultures and plant tissue. This is the first report of a pathogen of an eukaryotic vascular plant in the maritime Antarctic region.