Kirramyces destructans in Australia: biosecurity threat or elusive native pathogen?

Kirramyces destructans was first described in 1996 from north Sumatra, Indonesia, where it caused severe leaf and shoot blight on Eucalyptus grandis in nurseries and young plantations. Since then it has been reported in nurseries and plantations in Vietnam, Thailand and China, with its host range extending to include E. camaldulensis and E. urophylla. K. destructans has also been reported from native E. urophylla in East Timor and was considered a significant biosecurity threat to Australia’s native eucalypt forests and plantations. A study on the population diversity of K. destructans isolates throughout south-east Asia in which 8 gene regions were sequenced (four nuclear genes, one mitochondrial gene and three microsatellite markers) detected very low nucleotide polymorphism. This genetic uniformity is indicative of an introduced population which has subsequently spread throughout Asia via human-mediated movement of germplasm. Surveys of sentinel plantings in northern Australia revealed a complex of Kirramyces spp. among which K. destructans was detected. The same gene regions and markers were sequenced as for the Asian study and diversity among the K. destructans isolates in Australia was found to be much greater than that in Asia. We believe that K. destructans is native to Australia where is resides symptomlessly within the native vegetation. The disease is only expressed when non-endemic eucalypts are planted. As such the pathogen is a major encumbrance to the establishment of commercial eucalypt plantations in Northern Australia. The disease has not been observed in native ecosystems, but the effect of inoculum build up within plantations on adjacent native eucalypt remnants is not known