Phytophthora diversity and the population structure of Phytophthora ramorum in Swiss ornamental nurseries

Abstract

Invasive oomycete pathogens have been causing significant damage to native ecosystems worldwide for over a century. A recent well-known example is Phytophthora ramorum, the causal agent of sudden oak death, which emerged in the 1990s in Europe and North America. In Europe, this pathogen is mainly restricted to woody ornamentals in nurseries and public greens, while severe outbreaks in the wild have only been reported in the UK. This study presents the results of the P. ramorum survey conducted in Swiss nurseries between 2003 and 2011. In all 120 nurseries subjected to the plant passport system, the main P. ramorum hosts were visually checked for above ground infections. Phytophthora species were isolated from tissue showing symptoms and identified on the basis of the morphological features of the cultures and sequencing of the ribosomal ITS region. Phytophthora was detected on 125 plants (66 Viburnum, 58 Rhododendron and one Pieris). Phytophthora ramorum was the most frequent species (59Á2% of the plants), followed by P. plurivora, P. cactorum, P. citrophthora, P. cinnamomi, P. cactorum/P. hedraiandra, P. multivora and P. taxon PgChlamydo. The highest incidence of P. ramorum was observed on Viburnum 9 bodnantense. Microsatellite genotyping showed that the Swiss P. ramorum population is highly clonal and consists of seven genotypes (five previously reported in Europe, two new), all belonging to the European EU1 clonal lineage. It can therefore be assumed that P. ramorum entered Switzerland through nursery trade. Despite sanitation measures, repeated P. ramorum infections have been recorded in seven nurseries, suggesting either reintroduction or unsuccessful eradication efforts.

Development and Validation of Polymorphic Microsatellite Loci for the NA2 Lineage of Phytophthora ramorum from Whole Genome Sequence Data

“…Despite the increase over the MLG variation previously reported for the NA2 lineage in Canada, the level of variation observed within this lineage is still low compared with the variation present in the EU1 and the NA1 lineages in Europe, the United States, and Canada (Croucher et al 2013;Goss et al 2009Goss et al , 2011Grünwald et al 2012;Ivors et al 2004Ivors et al , 2006Prospero et al 2007Prospero et al , 2013Vercauteren et al 2010). For example, 53 MLGs have been reported in an analysis of 228 isolates of the NA1 lineage collected from American nurseries between 2004 and 2007 using eight microsatellite loci (Goss et al 2009).…”

“…Over the years, a wide range of molecular markers have been developed to identify, describe, and distinguish P. ramorum lineages, including microsatellites (Goss et al 2009;Ivors et al 2006;Mascheretti et al 2008;Prospero et al , 2007Vercauteren et al 2010Vercauteren et al , 2011b. These markers have been used to characterize the genetic diversity and migration patterns of P. ramorum in Europe and North America, especially for the EU1 and NA1 lineages (Croucher et al 2013;Goss et al 2009Goss et al , 2011Grünwald et al 2012;Prospero et al 2013;Vercauteren et al 2010). However, the EU2 and NA2 lineages remain poorly characterized.…”

Phytophthora chlamydospora

“…It has been associated with root rot of Port-Orford cedar (Chamaecyparis lawsoniana) in German nurseries, where it was initially misidentified as P. lateralis , and with root rot and stem cankers of Abies species in nurseries and Christmas tree plantations, where it was originally misidentified as P. drechsleri (Brasier et al 1993). On horticultural hosts, P. chlamydospora causes root and crown rot of walnut, almond, and cherry trees (Dervis et al 2016, Turkolnez et al 2016, Kurbetli et al 2017 and foliar lesions and shoot dieback on several ornamental species in nurseries (Jung and Blaschke 2004, Schwingle and Blanchette, 2008, Yakabe et al 2009, Blomquist et al 2012, Prospero et al 2013, Ginetti et al 2014.…”

Multispecies Phytophthora disease patterns in declining beech stands

“…Bark samples collected from bleeding lesions were surface-sterilized for 1 min in sodium hypochlorite solution (0.5%), rinsed twice in sterile distilled water for 30 s and dried on filter paper (Prospero, Vercauteren, Heungens, Belbahri, & Rigling, 2013). Samples were cut into small pieces of approximately 5 × 5 mm and divided into 2 subsamples.…”