APS Abstract of Presentation

Occurrence of Neonectria radicicola as a root pathogen of avocado in California
A. ESKALEN (1), V. T. McDonald (1)
(1) University of California, Riverside, CA, USA
Phytopathology 99:S33

Neonectria radicicola is known as a causal agent of root rot in grapevine, raspberry, ginseng and forest tree nurseries worldwide. Recently, N. radicicola has been reported to cause wilting of young avocado trees in nurseries in Israel. During a survey of major avocado growing areas of California in 2008, N. radicicola was isolated from roots of approximately 50% of trees showing symptoms of reduced vigor, dying shoots, and necrotic roots. Vascular elements of avocado feeder and secondary roots (1–3 mm diam.) were isolated onto potato dextrose agar amended with tetracycline (0.01%) and incubated at room temperature. Identification of the species was confirmed by colony and spore morphology and analysis of the internal transcribed spacer (ITS) regions ofrDNA. Pathogenicity of three different isolates of N. radicicola was tested by dipping roots of cv. Hass seedlings in a 10⁵ conidia per ml suspension for five min. The plants were then potted in soil and allowed to grow under greenhouse conditions. Leaves and shoots of inoculated plants developed wilting symptoms within 2 weeks and N. radicicola was consistently reisolated from necrotic roots. These results suggest that this fungus may have been overlooked as a root pathogen in CAand warrants further investigation.

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