β-Tubulin and histoneH3gene sequences distinguishCryphonectria cubensisfrom South Africa, Asia, and South America

Abstract

Cryphonectria cubensis (Bruner) Hodges is the causal agent of an important stem canker disease of Eucalyptus. Previous phylogenetic studies based on sequence data have shown that C. cubensis is distinct from other species of Cryphonectria but that C. cubensis isolates reside in two distinct groups, consistent with geographical origin. Thus, isolates of C. cubensis from South America and South Africa grouped together but apart from those originating from Southeast Asia and Australia. These results were in contrast with the symptoms of Cryphonectria canker in South Africa, which are different from those observed elsewhere in the world. The aim of this study was to use more variable regions of the fungal genome to test whether South African isolates of C. cubensis are genetically distinct from those from other parts of the world. For this comparison, β-tubulin and histone H3 gene sequences were used. Specimens from South America, Southeast Asia, Australia, and South Africa were also compared morphologically. The phylogram emerging from the analysis indicated that South American and Southeast Asian – Australian isolates resided in two well-resolved but closely related clades. However, isolates from South Africa were distinct from other groups. This is consistent with ecological aspects of the South African fungus, although no obvious morphological differences between the fungi from the various regions could be found. Our results suggest that the South African fungus represents a species distinct from C. cubensis occurring elsewhere in the world.Key words: β-tubulin, histone H3, molecular phylogeny, Cryphonectria cubensis.