04070nas a2200241   4500008004100000022001400041245008200055210006900137260001600206300002000222520335700242100001503599700001503614700001503629700002503644700001403669700001503683700001403698700002103712700001503733700001303748856006703761       2018                        eng d  a0191-291700aFirst Report of Phytophthora ramorum Causing Japanese Larch Dieback in France0 aFirst Report of Phytophthora ramorum Causing Japanese Larch Dieb  cAug-08-2018  aPDIS-02-18-02883 a<p><em>Phytophthora ramorum</em> Werres, De Cock &amp; Man in’t Veld, an oomycete known in the United States as the causal agent of sudden oak death, has spread across Europe since the early 2000s. It is responsible for damage and death to a wide range of plant species, including mature trees. In 2009 it was identified on Japanese larch (<em>Larix kaempferi</em>) in southwest England (<a id="b4" class="ref bibr"></a>Webber et al. 2010), and since then it has caused severe damage and losses to <em>Larix</em> spp. in the United Kingdom and the Republic of Ireland. There are two lineages of the oomycete, EU1 and EU2, found in Europe (<a id="b2" class="ref bibr"></a>King et al. 2015), EU2 being the more aggressive. The symptoms on larch include necrosis and loss of needles, wilting of shoots, dieback of branches, and death, often with abundant resin bleeding on trunks and branches. As sporulating hosts, <em>Larix</em> spp. may disperse <em>P. ramorum</em> over long distances. In May 2017, wilting, yellowing/reddening needles, and branch mortality were observed on mature <em>Larix kaempferi</em> (about 50 years old) in the forest of Saint-Cadou, Finistère, in the far northwestern part of France (3°59′49.2″ W; 48°22′22.4″ N). Approximately, 27% of the trees were affected in May, and 42% later in September 2017. The presence of <em>P. ramorum</em> was suspected and was first confirmed by testing samples collected from trunks and branches with necrosis and resin bleeds, using the specific conventional polymerase chain reaction (PCR) method developed by <a id="b1" class="ref bibr"></a>Ioos et al. (2006). The oomycete was also isolated in pure culture, using a <em>Phytophthora</em> selective medium (PARB[H]). The features observed, such as a coralloid mycelium, the presence of numerous thin-walled chlamydospores (up to 75 µm large), and deciduous, semipapillate sporangia arranged in clusters, matched those reported for <em>P. ramorum</em>. In June 2017, the presence of <em>P. ramorum</em> was confirmed in another larch stand in Hanvec, Finistère (4°12′45.0″ W; 48°20′10.8″ N), using the same identification techniques. In this stand, the prevalence was not precisely estimated but was deemed much lower than in Saint-Cadou. Based on the analysis of <em>Cox1</em> partial sequence and the PCR restriction fragment length polymorphism pattern described by <a id="b3" class="ref bibr"></a>Van Poucke et al. (2012) on <em>Cox1</em>, the <em>P. ramorum</em> isolates collected in these two forests could be assigned to the EU1 lineage. This is the first report of <em>P. ramorum</em> affecting Japanese larch in France and in mainland Europe. Until now it had only been detected on shrubs in nurseries, green spaces, and in rare circumstances in the natural environment on understory vegetation (rhododendron) in Normandy and Brittany, but not in the vicinity of the infected larch stands. The presence of this pathogen in the natural environment represents a major threat for larch trees, but also for the other potential forest host trees in this region, such as sweet chestnut, and might have a severe impact on both forest and ornamental tree species. Research is in progress to learn more about this outbreak, the possible origin of the inoculum, the extension of the disease, and its progression.</p>1 aSchenck, N1 aSaurat, C.1 aGuinet, C.1 aFourrier-Jeandel, C.1 aRoche, L.1 aBouvet, A.1 aHusson, C1 aSaintonge, F.-X.1 aContal, C.1 aIoos, R.  uhttps://apsjournals.apsnet.org/doi/10.1094/PDIS-02-18-0288-PDN