Quambalaria spp.: Emerging Tree Pathogens of Concern

Abstract Purpose of Review Quambalaria spp. are fungal pathogens originating from Australian eucalypt species that are becoming increasingly important globally. For example, Quambalaria eucalypti, which was once considered a minor pathogen, now poses a significant threat to plantation productivity and forest health across continents. Their spread has been made possible through the expansion of eucalypt plantation forestry outside Australia, the movement of plant material and the increase in travel and trade, which facilitates the intercontinental movement of pathogens. This review summarises current knowledge regarding the taxonomy, distribution, life cycle and ecological and commercial impacts of Quambalaria spp. and some considerations for their control. Recent Findings Recent studies have discovered new species of Quambalaria and there is emerging evidence of host shifts to other genera in the Myrtaceae. Outbreaks in Brazil, China, Indonesia and South Africa illustrate the rapid spread of Quambalaria spp. to new plantation environments. These pathogens threaten eucalypt plantations worldwide because clonal propagation reduces tree diversity and the trade of plant material facilitates their spread. Evidence of sexual reproduction has been identified in one species, Quambalaria pitereka , alluding to a high evolutionary potential. Although new molecular diagnostics and resistance screening tools are emerging, their use in the control of these pathogens remains limited. Summary Quambalaria spp. are important tree pathogens that are increasing their impact beyond their ancestral home in Australia. Their impact on plantation forestry and native forests underscores the broader vulnerabilities of forest ecosystems. Mitigating their impact will require integrated approaches that combine resistance breeding, enhanced surveillance, stringent quarantine measures, integrated disease management and changes to silviculture. Further research into host range, infection biology and pathogen evolution and the development of effective disease control is essential to safeguard global forests and ensure sustainable plantation forestry.