First report of Ganoderma colossus on Delonix regia in Oman

The flame tree (Delonix regia) is an important introduced amenity tree in Oman. It is planted on roadsides, in parks and public gardens for its beautiful flowers and elegant fernlike, bi-pinnate leaves. It is an excellent heat-tolerant plant, with moderate water needs. At Sultan Qaboos University, Oman in September 2003, several Delonix trees developed bracket-like, spongy, sessile basidocarps, which were yellow above and brown below (Fig. 1A). Around 20 severely infected trees were examined and uprooted. These displayed symptoms of leaf yellowing and branch death. An increase in the incidence of leaf yellowing, with branch and plant death was observed during the summer period (average temperature 40°C). Basidiocarps emerging from branches and tree trunks caused cracking of the bark followed by secretions of dark brown gummy substances. The brackets were identified as Ganoderma colossus# at Royal Botanic Garden Kew (RBGK), United Kingdom. The basidiospores were brown, ovate, rough-walled, bitunicate, 14-16 x 9-11 mm (Fig. 1B).

The only previous record of this fungus on Delonix regia, that we are aware of, is from Vietnam (Kleinwachter et al., 2001). In this case no external symptoms were recorded, such as the leaf yellowing and branch death observed in Oman. G. colossus is a pantropical species, which has been reported on a range of species. The species was originally described from Costa Rica and occurs on Phoenix canariensis, Ficus carica and Celtis laevigata in the USA (Adaskaveg & Gilbertson, 1988) and as a root and stem rot pathogen of pine, eucalyptus and Callitris in South Africa (Luckhoff, 1955). Specimens of G. colossus are held at RBGK originating from Saudi Arabia (date palm), Malaysia and Sierra Leone (oil palm), Pakistan (bamboo) and on Gmelina arborea from Nigeria.

This is the first record of G. colossus on D. regia in Oman and research is now underway at Sultan Qaboos University to examine its implications for D. regia and the economically important date palms (Phoenix dactylifera). We suspect that the source of the infection is the imported peat moss used for improving the soil. The same fungus has also been observed infecting Ficus altissima at the same campus (Elshafie et al., 2004).

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