Characterization of bronze leaf disease in western Canadian aspen and poplar trees

Aspen and poplar trees are important horticultural plants grown in Canada for aesthetic, commercial woodlot and windbreak applications. Bronze leaf is a destructive disease in Populus spp. and is caused by the fungal pathogen Apioplagiostoma populi Barr. This pathogen is often difficult to isolate and confirm from infected plant tissues and has been mainly identified by disease symptoms and morphological characteristics of A. populi when fruiting bodies form on infected leaves or branches. Affected leaves and branches typically become necrotic and bronze in colour. Air-borne spores and nursery shipments containing infected plants play an important role in the efficient movement of the pathogen. In this study, bronze leaf disease samples from symptomatic trees in Canada were examined microscopically for A. populi perithecia and asci. Pathogen-specific genomic sequences were identified for the development of sensitive stringent diagnostics that indicated branches and petioles were the most effective tissues for detecting A. populi. Leaf samples from symptomatic trees were collected in Canada and examined for perithecia to microscopically characterize A. populi asci and ascospores. Disease associated DNA sequences of the internal transcribed spacer (ITS) 5.8S region of the nuclear ribosomal, [beta]-tubulin 2, and translation elongation factor-1-[gamma] chain, were isolated from perithecia and symptomatic tree samples. Morphological and molecular biological data from this study characterized the relationship and epidemiology of A. populi and enabled the development of rapid diagnostic methods that restrict the extent of further losses in amenity and commercial plantings of aspen and poplar.