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Evaluation of Olive as a Host of Xylella fastidiosa and Associated Sharpshooter Vectors

September 2014 , Volume 98 , Number  9
Pages  1,186 - 1,193

Rodrigo Krugner, Mark S. Sisterson, Jianchi Chen, and Drake C. Stenger, United States Department of Agriculture—Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, Parlier, CA 93648; and Marshall W. Johnson, Department of Entomology, University of California, Riverside 92521

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Accepted for publication 20 March 2014.

Olive (Olea europaea) trees exhibiting leaf scorch or branch dieback symptoms in California were surveyed for the xylem-limited, fastidious bacterium Xylella fastidiosa. Only approximately 17% of diseased trees tested positive for X. fastidiosa by polymerase chain reaction, and disease symptoms could not be attributed to X. fastidiosa infection of olive in greenhouse pathogenicity assays. Six strains of X. fastidiosa were isolated from olive in Southern California. Molecular assays identified strains recovered from olive as belonging to X. fastidiosa subsp. multiplex. Pathogenicity testing of olive strains on grapevine and almond confirmed that X. fastidiosa strains isolated from olive yield disease phenotypes on almond and grapevine typical of those expected for subsp. multiplex. Mechanical inoculation of X. fastidiosa olive strains to olive resulted in infection at low efficiency but infections remained asymptomatic and tended to be self-limiting. Vector transmission assays demonstrated that glassy-winged sharpshooter (Homalodisca vitripennis) could transmit strains of both subspp. multiplex and fastidiosa to olive at low efficiency. Insect trapping data indicated that two vectors of X. fastidiosa, glassy-winged sharpshooter and green sharpshooter (Draeculacephala minerva), were active in olive orchards. Collectively, the data indicate that X. fastidiosa did not cause olive leaf scorch or branch dieback but olive may contribute to the epidemiology of X. fastidiosa-elicited diseases in California. Olive may serve as an alternative, albeit suboptimal, host of X. fastidiosa. Olive also may be a refuge where sharpshooter vectors evade intensive areawide insecticide treatment of citrus, the primary control method used in California to limit glassy-winged sharpshooter populations and, indirectly, epidemics of Pierce's disease of grapevine.

This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2014.