Population structure of the fungal pathogen Holocryphia eucalypti in Australia and South Africa

Holocryphia eucalypti is a fungal pathogen that causes stem cankers on Eucalyptus species in South Africa and Australia. In South Africa it is considered opportunistic but in Australia it has been associated with occasional but serious disease problems. The aim of this study was to determine the genetic structure of a South African population of H. eucalypti and compare it with three Australian populations of the fungus. Seventy-two isolates from Eucalyptus spp. and clones in South Africa were compared with 30 isolates from E. globulus and 24 isolates from Corymbia calophylla in the south of Western Australia and 23 isolates from E. dunnii in eastern Australia. DNA of these isolates was amplified using eight pairs of microsatellite markers previously developed for H. eucalypti . Nei’s gene diversity (H) showed that the eastern Australian population is the most genetically diverse and the Western Australian populations from Corymbia and Eucalyptus are somewhat less diverse. The South African population displayed the lowest genetic diversity. The high genetic diversity in the Australian populations supports the view that H. eucalypti is native to that region and was introduced into South Africa.