Olea europaea) in Argentina cover about 87 000hectares mainly located in Catamarca, La Rioja and San Juan areas.Following several reports of decline symptoms, a disease survey wasconducted during the spring 2005 in 30 olive plantations ranging from 300to 4000 ha. Crown dieback and root rot symptoms were recorded with anaverage incidence of 3% in Catamarca, 50% in La Rioja and 10% in SanJuan plantations. The disease incidence has increased year by year.A Phytophthora sp. was consistently isolated from rotted rootlets onselective V8 medium (PARPNH) (Jung et al., 1996). Isolates producedpapillate, caducous sporangia of variable shape, mostly elliptical to ovoid,and chlamydospores; all typical characteristics of P. palmivora. PCRamplicons generated using primers ITS 6 and ITS 4 (Cooke et al., 2000)were sequenced and found identical to those of P. palmivora from theNCBI GenBank database, thus confirming the morphological diagnosis.The pathogenicity of two P. palmivora isolates was tested by soil infes-tation in a growth chamber at 25 °C, using 15 one-year-old olive seedlingsper isolate. Uninoculated seedlings were used as negative control. Theinoculum was produced on autoclaved millet grains moistened with V8juice. Fifty days after inoculation the treated plants showed symptomssimilar to the ones observed in the field; necrotic leaves, defoliation and areduction of the root system of up to 40%. Control plants remainedhealthy, whilst P. palmivora was reisolated from roots of plants expressingsymptoms.The pathogen may have been introduced through rooted olive plants ofMediterranean varieties currently used in Argentina. Phytophthorapalmivora has recently been described as the causal agent of root rot ofolive in Italy, where it was isolated from collapsed olive trees (Cacciolaet al., 2000). In Spain it has been confirmed as a pathogen of olivealthough P. megasperma is more commonly associated with field symptoms(Hernandez et al., 1998). Alternatively, P. palmivora may have beenmoved to olive trees from other host species: P. palmivora infects morethan 200 species of ornamental, shade and hedge plants, mostly fromtropical areas. In Argentina, for instance, P. palmivora was recorded forthe first time in 1937 associated with Citrus spp.This is the first report of root rot caused by P. palmivora on olive grovesin Argentina. Due to the severe symptoms and the increasing incidencerecorded, P. palmivora should be considered a potential threat to olivecultivation in Argentina.References