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Die‐back and canker of several Eucalyptus species and clones were observed during a survey of the most important forestry areas of South Africa. Disease was often associated with extreme environmental conditions such as drought, hot winds and frost. Botryosphaeria dothidea, which is well known as a cause of canker and die‐back of Eucalyptus in other countries, was consistently isolated from symptomatic trees. Artificial inoculations of Eucalyptus nitens resulted in lesion development, confirming the pathogenicity of 5. dothidea to Eucalyptus in South Africa. This is the first report of this disease in South Africa.

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Sphaeropsis sapinea is the most important pathogen of Pinus spp. in South Africa. The fungus, which reproduces only asexually, occurs on exotic Pinus spp. In this study, the diversity of the S. sapinea population in South Africa was compared with a population from Northern Sumatra. The populations for both countries were obtained from exotic Pinus patula plantations. The phenotypic diversity of these populations was assessed using vegetative compatibility tests. The percent maximum genotypic diversity, based on Stoddart and Taylor's index, for the South African population was 30.5% compared with 1.5% for the Northern Sumatran population. Based on the number of phenotypes, the South African S. sapinea population was significantly more diverse (P = 0.05) than that of the Northern Sumatran population. The results indicate that the population of S. sapinea in South Africa has, in all likelihood, arisen as a result of introductions of the fungus on pine seeds imported from various parts of the world during the last century.