Submitted to: Phytoparasitica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2012
Publication Date: 7/1/2012
Citation: Mendel, Z., Protasov, A., Sharon, M., Ben-Yehuda, S., O'Donnell, K., Rabaglia, R., Wysoki, M., Freeman, S. 2012. An Asian ambrosia beetle Euwallacea fornicatus and its novel symbiotic fungus Fusarium sp. pose a serious threat to the Israeli avocado industry. Phytoparasitica. 40(3):235-238. Interpretive Summary: Wilt of avocado has become a serious constraint to the production of this economically important crop in Israel. Dead and dying avocado trees are all being attacked by the wood boring exotic beetle, Euwallacea fornicatus, which is native to Asia. In addition, we consistently isolated a fungus in the genus Fusarium from specialized cavities in the beetles called mycangia and from tunnels dug by the beetles in the avocado trees where the adult females rear their young. As in the case of other so-called ambrosia beetles, the fungus appears to be a major source of food for the larvae of this invasive insect. To determine whether the fungus was responsible for the disease symptoms, we inoculated healthy avocado trees with isolates of the Fusarium fungus. The results of this experiment showed that the fungus was responsible for the wilt symptoms. DNA typing of the fungal pathogen revealed that it represents a novel, unnamed phylogenetically distinct species within the Fusarium solani species complex. These analyses also indicate that the avocado pathogen is most closely related to F. ambrosium, another species farmed by E. fornicatus in the galleries of Chinese tea (Camellia sinensis) in India. Our study has revealed that the beetle and its symbiotic fungus have become a serious threat to the future of the avocado industry in Israel. The results of this study should be of interest to plant pathologists, plant breeders and quarantine officials charged with containing the spread of the economically devastating wood-boring beetle and its pathogenic symbiont, especially given the beetle’s broad host range of tree species.
Technical Abstract: The ambrosia beetle Euwallacea fornicatus Einchoff was first recorded in Israel in 2009. A novel unnamed symbiotic species within Clade 3 of the Fusarium solani species complex, carried in the mandibular mycangia of the beetle, is responsible for the typical wilt symptoms inflicted on avocado (Persea americana Mill.) trees. The beetle and its symbiotic fungus have become a serious threat to the future of the avocado industry in Israel.