First outbreak of pitch canker in a South African pine plantation

Fusarium circinatum, the causal agent of pitch canker, was first reported in South Africa in 1990 on Pinus patula seedlings in a nursery. Subsequent to this outbreak the pathogen has spread throughout South African pine nurseries causing a serious root and collar rot disease of various Pinus spp. The stem canker disease on plantation trees that typifies pitch canker in other parts of the world has never been observed in South Africa. An outbreak of a serious disease with symptoms resembling those of pitch canker on 5- and 9-year-old P. radiata in the Western Cape Province, prompted a study to determine the causal agent. Besides having stem cankers exuding copious amounts of resin, dying trees were infested by the weevil, Pissodes nemorensis. Isolations were thus made from infected tissue, weevil galleries and from adult insects. A Fusarium sp. was consistently isolated from both pine tissue and insects. The fungus was characterised based on morphological features and using DNA sequence comparisons for the genes encoding translation elongation factor 1-alpha and beta-tubulin. These studies showed conclusively that the fungus represents the pitch canker fungus, F. circinatum. Three isolates from trees in the affected area were inoculated onto P. radiata seedlings and their ability to cause disease was thus evaluated. Three weeks after inoculation, die-back symptoms were recorded on all inoculated plants. This report represents the first outbreak of pitch canker on plantation trees in South Africa. The fungus can thus no longer be considered only as a nursery pathogen in the country, where it seriously threatens the future of plantation forestry.