@article {4311, title = {Phytophthora siskiyouensis causing stem lesions and cankers on Alnus incana}, journal = {New Disease Reports}, volume = {31}, year = {2015}, month = {Jun-06-2017}, pages = {17}, abstract = {

In late summer 2013, stem cankers and sparse foliage were reported on European grey alder (Alnus incana) growing on a 500 ha site recently-planted with broadleaf and coniferous trees in south-west England. A site visit showed that approximately 10\% of\  more than 1000 grey alders (thought to have been imported from Europe and planted in the late 1990s) had symptoms including bleeding stem lesions similar to those caused by Phytophthora alni (Gibbs et al., 2003). In November 2013, samples were collected from stem lesions (Fig. 1), roots (internal lesions tracking-down from stem lesions) and rhizosphere soil from symptom-bearing trees. Tissue from root and stem lesion margins was plated onto Phytophthora selective medium (SMA) (amended as per Brasier et al., 2005) and incubated at 20{\textdegree}C for 48 hrs. Green apples were used as baits for soil samples by inserting a few grams of soil under a flap cut in the side of the apple and incubating for 4-7 days at 20{\textdegree}C. Isolation from developing SMA mycelial cultures and incubated apple baits onto potato dextrose agar (PDA) and carrot agar (CA) was then undertaken.

After 14 days on PDA at 20{\textdegree}C in the dark, colonies exhibited a distinctive stellate growth pattern (Fig. 2a). On CA they had a diffuse {\textquoteright}frosty{\textquoteright} appearance (Fig. 2b). On CA, oogonia with predominantly paragynous antheridia and aplerotic oospores were abundant. Partially-caducous sporangia formed when plugs from colonies on CA were submerged in unsterile pond water held at 20{\textdegree}C in the dark. Sporangia (46-51 μm wide) were semi-papillate and were ovoid, reniform, elongated or irregular in shape (Fig. 3). Sporangial morphology and dimensions corresponded to Phytophthora siskiyouensis (Reeser et al., 2007) and sequences of ITS and coxII regions supported this identification (GenBank Accession Nos. KP207601 and KP207602).\ 

One isolate of P. siskiyouensis was obtained from each of three different symptomatic trees; one from a root lesion, one from a stem lesion and one from associated soil. Koch{\textquoteright}s postulates were tested by inoculating two-year-old potted A. incana saplings with the three isolates. A small wound was made on the stem 10 cm above soil level. A CA plug colonised by P. siskiyouensis was inserted and the wound was sealed with Parafilm. Nine saplings were inoculated per isolate and maintained at 20{\textdegree}C with a 12-hr-photoperiod. Three control saplings were inoculated with sterile CA plugs. After 20 days, cankers and bleeding were visible externally on all of the trees inoculated with P. siskiyouensis (Fig. 4). The bark was peeled away to reveal phloem lesions extending approximately 2-4 cm above and below the inoculation point. No lesions developed on control trees. After re-isolation onto SMA, a Phytophthora sp. was recovered from all of the inoculated trees but not from the controls and it was identified as P. siskiyouensis by morphology (Reeser et al., 2007) and sequencing of the ITS region.

Phytophthora siskiyouensis is a recently-described species in the USA, isolated from stem lesions on myrtlewood (Umbellularia californica) and tanoak (Lithocarpus densiflorus; synonym of Nothocarpus densiflorus) and from soil and stream water, in south-west Oregon (Reeser et al., 2007). It has also been reported causing stem lesions on Italian alder (Alnus cordata) in California (Rooney-Latham et al., 2007). This is the first report of P. siskiyouensis in the UK and, to our knowledge, in Europe, and the first report of P. siskiyouensis causing stem cankers on A. incana. Its occurrence within a recently-planted site suggests a possible origin on introduced nursery stock. P. siskiyouensis has the potential to cause further damage to Alnus spp. and other plant species in Europe. Its comparative pathogenicity on various alder species is under investigation.

}, doi = {10.5197/j.2044-0588.2015.03110.5197/j.2044-0588.2015.031.017}, url = {http://www.ndrs.org.uk/contents.php?vol=31http://www.ndrs.org.uk/article.php?id=031017}, author = {P{\'e}rez-Sierra, A. and Kalantarzadeh, M. and Sancisi-Frey, S. and Brasier, C.M.} } @article {4004, title = {Previously unrecorded low-temperature Phytophthora species associated with Quercus decline in a Mediterranean forest in eastern Spain}, journal = {Forest Pathology}, volume = {43}, year = {2013}, month = {08/2013}, pages = {331{\textendash}339}, abstract = {

Oak decline has been a serious problem in Europe since the beginning of the twentieth century. In south-west Spain, Quercus ilex and Q.\ suber are the main affected species, and their decline has been associated with Phytophthora cinnamomi. During the last 10\ years, a severe decline of Q.\ ilex and Q.\ faginea accompanied by a significant decrease in the production of acorns affecting natural regeneration was observed in the eastern part of the Iberian Peninsula. Therefore, the aim of this study was to investigate the possible involvement of Phytophthora spp. in the decline. A forest in the Natural Park {\textquoteleft}Carrascar de la Font Roja{\textquoteright} in Comunidad Valenciana (eastern Spain), which is dominated by Q.\ ilex and Q.\ faginea, was surveyed during 2010{\textendash}2011. Symptomatic trees showed thinning and dieback of the crown, withering of leaves and death. An extensive loss of both lateral small woody roots and fine roots and callusing or open cankers on suberized roots were observed. Soil samples containing fine roots were baited using both Q.\ robur leaves and apple fruits. Six Phytophthora species were isolated: P.\ cryptogea, P.\ gonapodyides, P.\ megasperma, P.\ quercina, P.\ psychrophila and P.\ syringae. These are the first records of P.\ quercina and P.\ psychrophila on Q. faginea, of P.\ quercina in Spain and of P.\ psychrophila in mainland Spain. A soil infestation trial was conducted for 6\ months under controlled conditions with 1-year-old seedlings of Q.\ ilex and Q.\ faginea. Phytophthora cinnamomi was included in the pathogenicity test for comparison. The results showed that Q.\ ilex seedlings were generally more susceptible to infection than Q.\ faginea with P.\ cinnamomi being the most aggressive pathogen to both oak species. The two most commonly isolated Phytophthora species, P.\ quercina and P.\ psychrophila, also proved their pathogenicity towards both Q.\ ilex and Q.\ faginea.

}, issn = {1439-0329}, doi = {10.1111/efp.12037}, url = {http://dx.doi.org/10.1111/efp.12037}, author = {P{\'e}rez-Sierra, A. and L{\'o}pez-Garc{\'\i}a, C. and Le{\'o}n, M. and Garc{\'\i}a-Jim{\'e}nez, J. and Abad-Campos, P. and T. Jung} }