Type: Xylophilous Fungi; Description: Ascomata perithecial, superficial, attached to the medium by brown rhizoidal hyphae, globose with a long neck, black, 0.1 mm in diameter, perithecial necks straight to slightly curved, black, 300–900 m long, ostiolar hyphae divergent, septate, 20–70 tm long, hyaline. Asci evanescent. Ascospores allantoid, 0-septate, 4–6 × 1–2 am, smooth, hyaline. The following description applies to cultures of New Zealand isolates grown on 2% malt extract agar. Colonies greyish white to cream white, diurnal zonation strong, striate, petaloid or lobed, aerial mycelium aggregated into strands. Sporothrix synanamorph: common. Conidiophores lateral, 10–50 μm long. Conidia borne on short denticles produced sympodially, elliptical to elongate cylindrical, 0-septate, 4–15 × 2–4 μm, smooth, hyaline. Conidia also produced directly from the myelium, becoming aggregated into slimy droplets. Pesotum synanamorph: produced occasionally in old cultures. Conidiophores aggregated into synnemata, dark brown to black, 1–2 mm long, attached to the medium by brown rhizoidal hyphae; conidiogenous cells apical, borne on hyaline penicillate branches and forming a head. Conidia oval to ellipsoid, 0-septate, 2–6 × 1–3 μm, smooth, hyaline, aggregated into slimy droplets.

Distribution: Auckland (metropolitan region only), Hawkes Bay (Napier; sub-sequently eradicated).; 1st Record: Bain (1991).

Notes: Two major forms or races of O. novo-ulmi known as EAN (Eurasian) and NAN (North American) have been recognised (Brasier 1979). The New Zealand population of O. novo-ulmi is considered to belong to a single clone of the NAN European Vegetative Compatibility Supergroup (C.Brasier, Alice Holt Research Station, Surrey, UK, pers. comm.). Ophiostoma novo-ulmi is transmitted by scolytid bark beetles. In New Zealand, the only vector present is the small elm bark beetle, Scolytus multistriatus Marsham. The fungal anamorphs sporulate in tunnels made by the beetle and conidia are accidentally picked up by emerging adults. Ophiostoma novo-ulmi is heterothallic with two compatibility types, A and B. New Zealand isolates belong to the B-type. Ascomata were obtained only when conidia from A-type cultures imported from England were brushed on to the surface of the New Zealand cultures.

Significance: The cause of ‘Dutch elm disease’ which has been responsible for the death of most of the elms in Europe and North America (Brasier 2000). In New Zealand it was first detected in Myers Park, central Auckland, in December 1989. A delimiting survey showed that the disease was present in an area approximately 8 × 5 km in the Auckland metropolitan area and an eradication campaign was started immediately. The number of infected elms detected was relatively high at first (83 in 1989–90; an average of 20 per year between 1990–91 and 1994–95). From 1995–96 to 1998–99, only one or two infected trees were found and destroyed each year. Disestablishment of the Ministry of Forestry, which had been responsible for the eradication campaign up to 1998–99, was accompanied by a reduction in the intensity of the campaign. The number of infected trees has increased (11 were found in 2002–2003) and the success of the campaign, which seemed reasonably certain in 1998–99, is now in doubt. If the disease is allowed to spread, the entire New Zealand elm population is under threat. Although beetles carrying O. novo-ulmi have been found only in the metropolitan Auckland region, Scolytus multistriatus without the pathogen is currently (2005) found in an area between Warkworth to the north, Te Awamutu to the south, and Matamata and Te Aroha to the east. The distribution of the beetle appears to be expanding and there is no reason why it should not eventually reach all areas that have a population of elms. In 1993, a group of four trees in Sturm’s Gully reserve, Napier, was found to be infected with O. novo-ulmi. Isolates of the fungus were identical with those from Auckland trees. Intensive trapping using aggregating pheromones for S. multistriatus and S. scolytus failed to capture any Scolytus species and no signs of beetle activity were detected. In the absence of a vector, the disease remained confined to the gully, but continued to spread through root grafts. In view of the south-eastward progression of S. multistriatus, absence of the vector could not be guaranteed, and so all elms in the reserve were destroyed. The disease has not reappeared in Napier. It is not known how the fungus reached Napier in the absence of a vector.; Host(s): Ulmus americana, U. ×hollandica, U. ×vegeta, Ulmus sp. (Chinese species, e.g., Ulmus parvifolia and U. pumila, are resistant to infection.)

"C M Brasier (Forest Research Station, Alice Holt Lodge, Farnham, England, pers. comm.), who examined the initial seven isolates of O. novo-ulmi obtained obtained from diseased trees in Auckland. He found that all isolates were of the NAN Europeans vegetative compatibility supergroup, which is often the dominant vegetative compatibility group in western Europe at current epidemic fronts (Brasier 1988). He also considered that as all isolates were morphologically very similar, the outbreak may well comprise a single close of the NAN aggressive subgroup. The involvement of this group [points to western Europe as the most likely source of the New Zealand fungus."