A survey of Phytophthora in a beech forest in Norway

Abstract

During the past fifteen years there has been a widespread decline of mature European beech (Fagus sylvatica) in Europe and North America. The trees have shown typical symptoms of Phytophthora infection: root- and collar rot, bleeding cankers on the stem, and crown dieback. The isolation of P. cambivora from a beech tree and P. plurivora from a stream in Norway’s largest beech forest in Larvik in 2011, led to an extensive Phytophthora survey in 2012. Every tree in the beech forest in Larvik with a circumference above 20 cm was examined for bleeding cankers. Samples from the leading edge of the cankers were collected from selected trees, and water and soil were baited with Rhododendron leaves. Isolation was carried out on Phytophthora selective agar. The survey resulted in 54 trees with bleeding cankers on the stem. Two localities had a denser concentration of diseased trees than the rest of the forest, with 16 of 329 trees (4.9 %) and 12 of 680 trees (1.8 %). Four Phytophthora species were recovered in the survey and identified on the basis of morphology and the Internal Transcribed Spacer (ITS) region of ribosomal DNA. The survey yielded P. cambivora from beech, P. plurivora from soil and water, and P. gonapodyides and P. lacustris from water. All four species were pathogenic to beech seedlings in a pathogenicity test performed in 2013. In addition, experiments with Spanish slugs (Arion vulgaris) were conducted to examine whether slugs could act as vectors of Phytophthora spp. Results showed that hyphae were viable after passage through the digestive system of Spanish slugs. However, attempts to infect beech seedlings with slugs that had fed on Phytophthora, did not succeed.