First report of Ganoderma colossus on Ficus altissima in Oman

The lofty fig (Ficus altissima) is an important amenity tree in the Sultanate of Oman. Commonly planted on roadsides, in parks and public gardens, it grows well under the high temperature conditions of the Gulf region. During the summer of 2002 a large number of trees on the campus of Sultan Qaboos University, Muscat, began to show symptoms of leaf yellowing and branch dieback (Fig. 1).

Sheets of white mycelium were seen under the bark. From the trunks of affected trees, bracket-like, spongy, sessile basidiocarps appeared. These were initially rounded, pale brown above and cream-yellow below, eventually reaching a diameter of 20 cm and a thickness of 8 cm (Fig. 2). Trees died within six months of symptoms first appearing. Fruiting bodies were sent to the Royal Botanic Garden, Kew, UK (RBGK) and identified as Ganoderma colossus#. The basidiospores were brown, ovate with a rounded base and a truncate to narrowly rounded apex, bitunicate, measuring 14-16 x 9-11 μm (Fig. 2). Nearby apparently unaffected trees gave no indication of water stress and routine irrigation of trees took place during the period when trees were dying.

G. colossus is a thermophilic root and buttress pathogen that causes white rot disease on several tree species and has the capacity to cause extensive delignification of different types of timber. Elsewhere, this pathogen has been reported on Phoenix canariensis, Ficus carica and Celtis laerigata in the USA (Adaskaveg & Gilbertson, 1988) and on Delonix regia in Vietnam (Kleinwachter et al., 2001). As the reported hosts are also important amenity trees in Oman, with little possibility for disease management other than eradication of infected plants, future work is planned to determine the potential for disease transfer from F. altissima to other species. Most recently the pathogen has been reported on Delonix regia in Oman (Al-Bahry et al., 2004), enhancing the concern of spread to economically important species.

#Editor's note: G. colossus is also wrongly described as G. colossum, a common orthrographic error.