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A new pest: Fusarium sp. and its vector tea shot-hole borer (Euwallacea fornicatus) causing Fusarium dieback on avocado in California.
A. ESKALEN (1), D. H. Wang (1), M. Twizeyimana (1). (1) Department of Plant Pathology and Microbiology, University of California-Riverside, Riverside, CA, U.S.A.

The Asian ambrosia beetle (<i>Euwallacea fornicatus</i>) forms a symbiotic relationship with <i>Fusarium</i> sp. This beetle has recently been threatening the Israeli avocado industry. The beetle also causes severe damage on tea (<i>Camelia sinensis</i>) branches in Sri Lanka and India. In California, the beetle was first reported on black locust (<i>Robinia pseudoacacia</i>) in 2003, but there was no record of symbiotic fungus damage. Symptoms of white powdery exudate either dry or surrounded by wet discoloration of the outer bark in association with a single beetle exit hole were observed on several backyard avocado trees in South Gate, Downey and Pico Rivera, Los Angeles County, California in February and March 2012. While no visible injury to the bark was observed, examination of the cortex and wood under the infested spot bored by the beetle(<i>E. fornicatus</i>) revealed brown discolored necrosis caused by a fungus. Symptomatic cortex and sapwood tissues were plated onto PDA medium amended with tetracycline (0.01%). After 4 to 5 days of incubation at room temperature, fungal colonies akin to <i>Fusarium</i> sp. were produced. Fungal identification was determined by using the rDNA internal transcribed spacer (ITS) and elongation factor (EF1-α) primers. Pathogenicity tests were conducted by inoculating detached green shoots of healthy avocado trees. Lesions were observed on all inoculated shoots except for the control. Mean lesion lengths were 12.8 cm 3 weeks after inoculation. This is the first report of symbiotic <i>E. fornicatus</i> and <i>Fusarium</i> sp. on avocado in California.<p><p>Keywords: Fungus, Tropical-Subtropical Crops

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