Anisogramma anomala colonizes systematically the phloem, cambium and the outer xylem of branches and produces cankers only after one year incubation period or more. On American hazelnut (Corylus americana), this fungi causes an insignificant canker, measuring 1-10 cm in length. In contrast, on European hazelnut (Corylus avellana) the cankers can expand perennially at rates up to 1 m per year, girdling branches, causing canopy dieback and death of trees (Johnson et al. 1996).
The developmental morphology of A. anomala is described by Gottwald & Cameron (1979). A brief summary about their fungal description is given below.
This species produces multiple perithecia within a compact Diatrype-like stroma and apiosporous ascospores. On C. avellana, cankers contain up to 20 stromata (in single or double rows pattern) at the first year and hundreds of stromata (in three to five rows) from the second year on. Mature stroma are black and measures 1.5—3 x 2—10 mm and 1—2 mm in height. Perithecia, 40—60 per stroma, ovate to pyriform, 250-830 x 1040-2160 µm. Its wall measures 40—45 µm and its neck, 160—240 µm in diameter, which is often bulbous at the surface, near the ostiole, measuring up 350 µm in diameter. The size of the neck depends upon the perithecium position in the stroma. Asci broadly clavate, 10—15 x 45—65 µm, with a long, treadlike stipe, 8-spored. There are about 8,400 asci in a mature perithecium. Ascospores hyaline, two-celled, The smaller cell is completely degenerate and remains as a hemispherical cap cell on one end of the larger cell, measuring 1.1-1.4 x 1.1 µm. The larger cell measures 8—12 x 4—5 µm at the maturity.
1. Infected plants can remain symptomless for up to two years. Introduction of the pathogen to new areas via infected but symptomless nursery stock has been documented.
2. Prior to canker formation, incubating infections cause a brown discoloration in the outer xylem. The pathogen can be detected in the discolored tissues by an enzyme-linked immunoabsorbent assay (ELISA) or by visualizing A. anomala mycelium in hand-cut sections of the outer layer of xylem (Coyne et al. 1996).
3. A. anomala is considered biotrophic, and consequently is difficult to culture (Stone et al. 1994).