Abstract:
Cypress canker is a branch and stem canker disease of Cupressaceae trees, particularly those in the genera Cupressus and Hesperocyparis. These trees have been planted
in many parts of the world as ornamentals and the Seiridium species that cause the disease, consequently, also have an almost global distribution. The taxonomy of Seiridium
species causing cypress canker has recently been revised and numerous species are
now believed to cause the disease. This study describes, for the first time, cypress canker on the native South African Cupressaceae tree, Widdringtonia nodiflora. The aim
was to identify the causal agent and confirm its pathogenicity. Phylogenetic analyses
of sequence data for four regions identified the fungus as Seiridium neocupressi, a species previously known only from Australia, New Zealand and Italy. Field inoculations
of W. nodiflora branches resulted in distinct cankers within 6 weeks and the fungus
could be reisolated from the treated trees. Cypress canker has been known in South
Africa for many decades, where it causes a serious disease on nonnative species of
Cupressus, but it has never been found on native Cupressaceae. The newly discovered
disease caused by a probable alien pathogen is of particular concern because only
three species of Widdringtonia occur in South Africa and are important components
of the native flora. The two other species, W. wallichii and W. schwartzii, occur in small
endemic and threatened populations. The origin of S. neocupressi in South Africa and
the relative susceptibility of the three Widdringtonia species, consequently, requires
urgent attention.
