@article {4708, title = {Fitness characteristics of the European lineages of Phytophthora ramorum}, journal = {Plant Pathology}, volume = {70}, year = {2021}, month = {Oct-12-2020}, pages = {275 - 286}, abstract = {

As an introduced pathogen, Phytophthora ramorum exists as four near-clonal evolutionary lineages, of which only EU1 and EU2 are established in the UK. EU1 has become widespread since the first findings in 2002 whereas EU2, detected in 2011, has a more limited distribution. Both lineages are epidemic in plantation-grown larch, sporulating asexually on needles, but also causing heavy dieback and mortality. To understand whether EU1 and EU2 pose different threats to forest health, we compared their growth characteristics on agar, pathogenicity on several hosts, and sporulation on Japanese larch needles. When pathogenicity was evaluated by measuring colonization at 20\ {\textdegree}C in mature bark (phloem) of Japanese and European larch (Larix kaempferi and L. decidua), English oak (Quercus robur), and beech (Fagus sylvatica), Japanese larch was the most susceptible and oak the least susceptible. On average, EU2 isolates produced significantly larger lesions than EU1 isolates in Japanese larch and oak although not in the other hosts. With tests using young saplings of Japanese and European larch, damaging bark lesions formed at both 10\ {\textdegree}C and 20\ {\textdegree}C, but EU2 was significantly more pathogenic at 20\ {\textdegree}C on both hosts compared with EU1. In contrast, both lineages caused similar amounts of necrosis on inoculated leaves of rhododendron (Rhododendron ponticum). Moreover, EU2 isolates usually sporulated less abundantly on larch needles compared with EU1 isolates, suggesting a trade-off in pathogenicity and sporulation between lineages. As EU2 tends to have smaller sporangia than EU1, this could also reduce the inoculum potential of EU2.

}, issn = {0032-0862}, doi = {10.1111/ppa.v70.210.1111/ppa.13292}, url = {https://bsppjournals.onlinelibrary.wiley.com/doi/abs/10.1111/ppa.13292?af=R}, author = {Harris, Anna R. and Brasier, Clive M. and Scanu, Bruno and Webber, Joan F.} } @article {4689, title = {Insights into the potential host range of Phytophthora foliorum}, journal = {Forest Pathology}, volume = {49}, year = {2019}, month = {Sep-18-2019}, pages = {e12556}, abstract = {

During a survey for Phytophthora ramorum undertaken in north-west Scotland in early 2016, Phytophthora foliorum was found infecting foliage of the invasive shrub Rhododendron ponticum. Prior to this, P.\ foliorum had only been reported from foliage of hybrid azaleas in nurseries in California and Tennessee and from azalea plants in an ornamental nursery in Spain. No other hosts were known, and much of the behaviour of P.\ foliorum remained enigmatic. The species is classified in Phytophthora Clade 8c, with closest relatives, P.\ ramorum and Phytophthora lateralis, both of which are highly damaging tree pathogens. To explore the threat that P.\ foliorum might pose to trees, its growth{\textendash}temperature responses on agar media and ability to cause lesions in the living bark of various hosts were contrasted with the behaviours of P.\ ramorum and P.\ lateralis. Phytophthora foliorum proved faster growing and more tolerant of temperature extremes than the other Phytophthora species. Comparisons of bark colonization initially focussed on R.\ ponticum and larch species Larix decidua and Larix kaempferi as all three are significant hosts of P.\ ramorum in the UK. Further experiments included another P.\ ramorum host, Fagus sylvatica (European beech), and the main host of P.\ lateralis, Chamaecyparis lawsoniana (Lawson cypress). Findings suggested that as well as being a significant pathogen of R.\ ponticum, damage caused by P.\ foliorum to both species of larch and beech was very similar to that of the EU1 lineage of P.\ ramorum, although growth in host tissue was also influenced by season.

}, doi = {10.1111/efp.v49.610.1111/efp.12556}, url = {https://onlinelibrary.wiley.com/doi/10.1111/efp.12556}, author = {Harris, Anna R. and Webber, Joan F.} }