First report of Fusarium euwallaceae and its vector Euwallacea fornicatus sensu lato causing tree dieback in South Africa
Since the mid-2000s, an ambrosia beetle belonging to the species complex Euwallacea fornicatus (Coleoptera: Curculionidae – EPPO A2 List) and one of its obligate symbiotic fungi (Fusarium euwallaceae – EPPO A2 List) have been reported to cause dieback and mortality on avocado (Persea americana) and numerous other trees and shrubs in the USA and Israel. During routine surveys conducted in 2016 in botanical gardens of South Africa in the framework of the International Plant Sentinel Network (IPSN), the presence of an ambrosia beetle and its associated fungal symbiont were detected in Platanus x acerifolia (London plane) trees showing dieback symptoms in the KwaZulu-Natal National Botanical Garden in Pietermaritzburg. On infested tree trunks, the removal of the bark and cambium exposed insect galleries with lesions from which wood material was sampled. In addition, infested branches were also collected and dissected. Insect specimens and fungal isolates were collected and studied (morphological, molecular and pathogenicity tests). Results confirmed the presence of both E. fornicatus sensu lato and of F. euwallaceae in diseased plane trees. This is the first time that E. fornicatus sensu lato and its fungal symbiont, F. euwallaceae are reported to cause Fusarium dieback on trees in South Africa. The authors also stressed that this is also the first time that a damaging invasive forest pest has been detected through a sentinel tree research project, highlighting the value of such type of initiative. As both E. fornicatus sensu lato and F. euwallaceae represent a significant threat to many tree species in South Africa, it is noted that regulations should be envisaged to prevent their spread, as well as further surveys to determine their geographical distribution.
Sources
Paap T, de Beer ZW, Migliorini D, Nel WJ, Wingfield MJ (2018) The polyphagous shot hole borer (PSHB) and its fungal symbiont Fusarium euwallaceae: a new invasion in South Africa. Australasian Plant Pathology. https://doi.org/10.1007/s13313-018-0545-0