First report of Holocryphia eucalypti on Eucalyptus grandis in Uganda

Abstract

In recent years, Uganda has embarked on extensive establishment of plantations of fast growing eucalypts to meet local demand for construction timber. In 2007, stem cankers were observed on a small number of five year-old Eucalyptus grandis trees in a clonal trial in Kifu, near Kampala in Uganda. The cankers comprised shallow fissures with orange fruiting bodies, and a sharply defined necrosis at the canker edge. The cankers were similar to those caused by the fungus Holocryphia eucalypti on eucalypts in South Africa. The morphological characteristics of the conidia (aseptate, hyaline, cylindrical characteristics) and the orange stromata also matched published descriptions of H. eucalypti. Spore masses from orange fruiting bodies on the bark of several trees were aseptically transferred to malt extract agar plates. Using protocols from Gryzenhout et al. (2006), DNA sequences of the internally transcribed spacer regions ITS1 and ITS2 and 5.8S rRNA were obtained. The Ugandan isolate sequences (GenBank GQ292540) gave 100% bootstrap values when compared with known isolates of H. eucalypti. Greenhouse inoculation studies on one E. grandis clone under quarantine conditions in South Africa confirmed that H. eucalypti from Uganda was pathogenic. Stem inoculations with H. eucalypti on young trees (∼5 mm diam) produced lesions within three weeks of inoculation, while trees with control inoculations using sterile agar discs produced no lesions. The fungus was re-isolated from the lesions but not the control plants. Previously, H. eucalypti was known only from Australia and South Africa (Gryzenhout et al., 2006). In Australia, H. eucalypti is associated with more severe stem cankers and is considered an important pathogen of stressed trees especially (Wardlaw, 1999). Symptoms in Uganda were similar to that in South Africa, with no tree mortality observed and only the formation of superficial bark cankers. The implications of this disease for Uganda are unclear and further monitoring of its status is needed.