Publication Type:Journal Article
Source:Plant Disease, Volume 100, Issue 7, p.1508 - 1508 (2016)
Phytophthora pseudosyringae T. Jung & Delatour was described in 2003 as a pathogen associated with root and collar rot of several tree species (Fagus sylvatica, Alnus glutinosa, Quercus spp.) (Jung et al. 2003), and as the causal agent of stem lesions on beech in Europe (Scanu and Webber 2016). In August 2015, a beech (Fagus sylvatica L.) tree displaying 25% crown dieback and a bleeding canker at the base of the stem was observed in a forested area used for recreational purpose in Central Pyrenees (42°36.87′ N, 0°46.09′ E, 1,546 m above sea level). Coarse sections of wood surrounding the bleeding patches were sampled and kept moist and cold for 5 days until processed. Once in the laboratory, small phloem pieces from the margin of the lesion were plated onto corn meal agar-PARPBH medium (Jeffers and Martin 1986) and incubated at 20°C. Growing hyphae were transferred to V8 agar and incubated at 20°C in darkness. Colony growth on V8 medium averaged 3.4 cm/week and had a distinct stellate pattern. Sporangia were sympodial, semipapillate, and ovoid, with a length/breadth average ratio of 1.41 μm (SE = 0.02). Oogonia were 21.9 μm (SE = 0.49) in diameter, smoothly walled, spherical, and with paraginous antheridia, although some amphiginous antheridia were observed. Morphological features and growth appearance on V8 corresponded to those reported for P. pseudosyringae (Jung et al. 2003). DNA was extracted from mycelium, and the ITS region was amplified using the ITS4 and ITS6 primers (Cooke et al. 2000). A BLAST search of the sequenced isolate (submitted to GenBank, Accession No. KU321521) showed 100% identity with P. pseudosyringae ITS sequence (AY230190) from Jung et al. (2003). An under-bark inoculation test with mycelia plugs were performed on 16 excised shoots of 1 cm of diameter obtained from four different F. sylvatica trees. After 4 weeks, inoculated shoots displayed longer necrotic lesions than control inoculations with agar (3.55 cm SE: 2.2 versus 0.59 cm SE: 2.8, P < 0.0001). The P. pseudosyringae inoculated shoots exhibited lesions that were dark red underneath the bark, whereas the control lesions did not. P. pseudosyringae, which was identified morphologically, was reisolated from 40% of the infected shoots. No reisolation of the pathogen occurred from any of the six control shoots. Although previously detected in nursery stock on sweet chestnut (Castanea sativa) (Pintos Varela et al. 2007), our report represents the first report of P. pseudosyringae naturally affecting trees in Spain, and widens the geographical distribution of this pathogen in southwestern Europe. In Spain, F. sylvatica is the third species in terms of standing volume, where it covers 400,000 ha, mainly in the Pyrenees. Our finding proves the capacity of this pathogen to establish in nature, and it raises concern over the potential impact on beech forests in Spain.