Abstract
Two economically, environmentally and culturally important Australian native tree species, Araucaria cunninghamii (hoop pine) and A. bidwilli (bunya pine) are rapidly declining in the Bunya Mountains national park. Some of the affected bunya pines are estimated to be more than 600 years old. Symptoms include yellowing of the crown and rapid dieback, which is consistent with infection by Phytophthora, a fungal-like oomycete. Aerial surveys have shown that symptomatic trees of both species are spread throughout the national park. Phytophthora multivora, a pathogen associated with dieback of Eucalyptus gomphocephala and Pinus radiata in Western Australia, was isolated from the rhizosphere of symptomatic bunya pines. Phytophthora multivora has also been associated together with P. cinnamomi in the dieback of wollemi pine (Wollemia nobilis) in New South Wales, and kauri pine (Agathis australis) in New Zealand. Both pathogens have wide host ranges that include agriculturally and environmentally important plant species. DNA meta-barcoding analysis of the soil detected both pathogens at high numbers. Pathogenicity testing of the organisms is currently being conducted on bunya and hoop pine to confirm aggressiveness. Additional surveys and testing need to be conducted to confirm how wide spread the problem is, and to implement control measures to prevent future damage to the national park and surrounding softwood plantations. From initial observations of the symptoms, spread patterns and environmental history of the affected trees, P. multivora is the most likely causal agent of the dieback.