Phytophthora alni on Alnus glutinosa reported for the first time in Spain

Abstract

Since the mid 2000s extensive mortality of common alder (Alnus glutinosa) has been observed along many rivers of northern Spain (Tuset et al., 2006). Symptoms include sparse yellowish and small-sized foliage, dieback of branches, increased fruit production and dark-stained necrosis of the bark at the collar and lower stem. These resemble symptoms of the root and collar rot epidemic of alders which is caused by the different subspecies of the host-specific pathogen Phytophthora alni and has led to high mortality of riparian alders across 14 countries in Western, Central and Northern Europe (Gibbs et al., 2003; Jung & Blaschke, 2004). In September 2009, samples from five symptom-bearing A. glutinosa trees were collected along the river Miño (Lugo, Galicia, 42º59′N 7º32′W, 367 m above sea level). Bark samples, including the cambium, were taken from the upper 20 cm of the orange-brown active lesions, placed in distilled water and transported to the laboratory in cool jars. Over 2–3 days the water was replaced four times per day in order to remove excess polyphenols. Small pieces (c. 4 × 4 × 2 mm) were cut from the lesions, blotted dry and plated onto V8-PARPH agar (Jung & Blaschke, 2004). After five days incubation at 20°C, tentative Phytophthora isolates were obtained from four trees. The isolates were homothallic with amphigynous antheridia, predominantly two-celled, and produced ornamented, occasionally comma-shaped oogonia ranging from 33 to 50 μm in diameter. In soil-extract they produced nonpapillate, ellipsoid to ovoid sporangia (60 × 49 μm). On V8 agar, colonies had a slightly woolly morphology and showed radial growth rates of 3·6–7·5, 2·2–5·4 and 0·0 mm day−1 at 20, 25 and 30°C, respectively. These features resemble those of P. alni ssp. alni (Brasier et al., 2004). DNA of the ITS region was amplified as described previously (Cooke et al., 2000). The sequences of all isolates were identical (GU175431) and a Blast search at GenBank showed 99% identity with P. alni ssp. alni (AF139366.1). This is the first report of P. alni in the Iberian Peninsula. Additional surveys will be carried out, which will allow the administration to adopt proper management strategies. We thank O. Locos and to P. Abad-Campos. Supported by Consejerías ECI and IEMA (Junta de Extremadura, III-PRI 08-A78), University of Valladolid (061/060831), and Ministerio Educación y Ciencia (AGL2007-64690/AGR).