Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2013
Publication Date: 11/1/2013
Publication URL: http://handle.nal.usda.gov/10113/60349
Citation: Freeman, S., Sharon, M., Maymon, M., Mendel, Z., Protasov, A., Aoki, T., Eskalen, A., O'Donnell, K. 2013. Fusarium euwallaceae sp. nov.—a symbiotic fungus of Euwallacea sp., an invasive ambrosia beetle in Israel and California. Mycologia. 105(5):1595-1606. Interpretive Summary: We used morphological and molecular data to characterize the Fusarium fungus farmed by an invasive wood-boring beetle (Euwallacea sp.) from Asia that is currently attacking over 200 different tree species in Los Angeles County in southern California. In addition to significant economic losses due to death of diverse trees in the urban landscape, the beetle and the novel Fusarium sp. that it cultivates in trees as a source of nutrition pose a major threat to avocado production in California and Israel. Thus far the beetle has not been detected in the major commercial avocado groves north and south of Los Angeles, but it has been spreading through Israeli avocado groves since 2009. Our data indicated that the novel Fusarium farmed by the beetle is closely related to F. ambrosium, a fungus that is farmed by another species of wood-boring beetle that is a pest insect on Chinese tea in India and Sri Lanka. Both Fusarium species produce odd club-shaped spores by which they are dispersed by female beetles to new trees. Currently the DNA sequence data generated in the present study provides the most reliable method for accurately identifying the novel Fusarium, which we have described and illustrated as F. euwallaceae. Results of this study will be of interest to plant pathologists and entomologists who are charged with controlling the dieback and wilt diseases they vector and quarantine officials who are interested in preventing the spread of these economically destructive avocado pests.
Technical Abstract: The invasive Asian ambrosia beetle Euwallacea sp. (Coleoptera, Scolytinae, Xyleborini) and a novel Fusarium sp. that it farms in its galleries as a source of nutrition seriously damage over 20 species of live trees and pose a serious threat to avocado production (Persea americana) in Israel and California. Adult female beetles are equipped with mandibular mycangia in which its fungal symbiont is transported within and from the natal gallery. Damage they cause to xylem is associated with disease symptoms that include sugar or gum exudates, dieback, wilt, and ultimately host tree mortality. During 2012 the beetle was recorded on over 200 and 20 different urban landscape species in southern California and Israel, respectively. Euwallacea sp. and its symbiont are closely related to the tea shot-hole borer (E. fornicatus) and its obligate symbiont, F. ambrosium occurring in Sri Lanka and India. To distinguish these ambrosia beetles, hereafter the unnamed xyleborine in Israel and California will be referred to as Euwallacea sp. IS/CA. Both fusaria produce clavate macroconidia, which we interpret as an adaption for the symbiosis, and exhibit distinctive ecologies. Also both comprise a genealogically exclusive lineage within Clade 3 of the Fusarium solani species complex (FSSC) that can be differentiated using arbitrarily-primed PCR. Presently these fusaria can only be distinguished phenotypically by the abundant production of blue to brownish macroconidia in the symbiont of Euwallacea sp. IS/CA and their rarity or absence in F. ambrosium. We speculate that obligate symbiosis of Euwallacea – Fusarium may have driven ecological speciation in these mutualists. Thus, the purpose of this paper is to describe and illustrate the novel, economically destructive avocado pathogen as Fusarium euwallaceae sp. nov. S. Freeman et al.