The Etiology And Epidemiology Of Bleeding Canker On European Beech

Abstract

European beech (Fagus sylvatica) is an important forest and landscape tree. These trees are susceptible to attack by various Phytophthora species. A survey of these trees in the northeastern United States shows approximately 70% of trees have symptoms of this type of infection, when patches of necrotic bark on the root flares of trunk ooze dark or rusty colored liquid. Forty percent of symptomatic bark tissue yielded a Phytophthora isolate. The most frequent species associated with this disease were P. citricola and P. cactorum. Multiple gene phylogenetic analysis indicated that isolates classified as P. citricola can be divided into two distinct clades, P. citricola A and B. Phytophthora citricola A is most frequently found associated with bleeding canker symptoms, approximately 60% of the time, followed by P. cactorum approximately 30% of the time. Phytophthora citricola B, P. gonapodyides and P. cambivora were found rarely. All of these pathogens can be found in the soil surrounding both asymptomatic and symptomatic beech, although the frequency varies. All five pathogens cause necrotic symptoms when inoculated into European beech sapling stems. In addition, P. citricola A and B and P. cactorum can cause disease on leaf and stem tissue of Betula lenta, Syringa vulgaris and Ulmus americana, and they are able to cause disease on leaf tissue of Acer saccharum, Fraxinus americana, Viburnum trilobum and V. opulus. In addition, P. citricola A and B were able to cause lesions on leaves of Syringa reticulata and V. dentatum. The identification of the species associated with this disease and the knowledge of the role they play in the environment help as we try to develop ways to control this disease.