ARS | Publication request: A pernicious agent affecting avocado in Israel: a novel symbiotic Fusarium sp. associated with the ambrosia beetle Euwallacea fornicatus

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 15, 2012
Publication Date: February 15, 2012
Citation: Freeman, S., Protasov, A., Wysoki, M., Ben Yehuda, S., Noi, M., Rabaglia, R., O Donnell, K., Sharon, M., Zveibil, A., Eliyhu, M., Mendel, Z. 2012. A pernicious agent affecting avocado in Israel: a novel symbiotic Fusarium sp. associated with the ambrosia beetle Euwallacea fornicatus. Meeting Abstract.

Technical Abstract: Since first recorded in Israel in 2009, the ambrosia beetle, Euwallacea fornicatus Eichhoff, has been shown to vector a fusarial pathogen of avocado (Persea Americana Miller) in its mandibular mycangia. Multilocus molecular phylogenetic analyses indicate the pathogen represents a novel symbiotic Fusarium sp. within Clade 3 of the Fusarium solani species complex. Adult beetles and their larva feed on fungal mycelium that is inoculated into galleries within the xylem when adult females tunnel in the sapwood. The beetle attacks the major avocado cultivars in Israel, with Haas and Pinkerton appearing to be the most susceptible. In addition to avocado, the beetle also colonizes and develops on box elder (Acer negundo) and the castor oil plant (Ricinus communis) causing severe injury and tree mortality. Typical symptoms in avocado include discoloration of the outer bark surrounding the penetration spot, which is covered by a white powdery exudate termed 'persein.' While there is no visible injury to the cortex, xylem under the area bored by the beetle is stained brown and becomes necrotic. Additional symptoms include: (i) wilting of branches and discoloration of leaves; (ii) wilting and collapse of branches laden with yield; and (iii) mortality of trees. Koch postulate tests were performed successfully with the symbiotic Fusarium sp. on detached branches and in an experimental plot of an avocado orchard in Volcani Center. The beetle-fungus complex has become a serious threat to the future of the avocado industry in Israel.