First Report of Phytophthora palmivora as a Pathogen of Olive in Italy.

Olive (Olea europea L.) is an economically important crop in Italy and is planted on about 1 million ha. The Apulia, Calabria, and Sicily regions of Southern Italy account for about 70% of the production. Many new plantations have been established during the last 10 years. In summer 1999, 1- to 2-year-old olive trees (cv. Carolea) with decline symptoms were observed in new plantations in Catanzaro Province (Calabria). The symptoms associated with the root rot were leaf chlorosis, defoliation, wilting, twig dieback, and eventual plant collapse. In some cases, more than 40% of the trees were affected. A Phytophthora sp. was isolated consistently from rotted rootlets of diseased trees using a selective medium (2). Single-zoospore isolates were obtained from the colonies. The species isolated from olive roots was identified as P. palmivora (E. Butler) E. Butler on the basis of morphological and cultural characters according to Erwin and Ribeiro (1). All isolates produced papillate sporangia, which were elliptical to ovoid, caducous (mean pedicel length = 5 µm), with a length-breadth ratio of 1.8. In addition, some isolates produced subglobose, non-papillate sporangia with a length-breadth ratio ranging from 1.2 to 1.5. Electrophoresis of mycelial proteins on polyacrylamide gels confirmed that all isolates were pure cultures and that they all belonged to the same species. The electrophoretic banding patterns of total soluble mycelial proteins and eight isozymes (alkaline phosphatase, esterase, fumarase, NAD-glucose dehydrogenase, glucose-6-phosphate dehydrogenase, lactate dehydrogenase, malate dehydrogenase, and superoxide dismutase) of all olive isolates were identical to those of two strains of P. palmivora from parlor palm and from pittosporum. Conversely, they were clearly distinct from the electrophoretic banding patterns of reference isolates of P. cactorum (Lebert & Cohn) Schroter, P. capsici Leonian, P. citrophthora (R. E. Sm. & E. H. Sm.) Leonian, and P. nicotianae van Breda de Haan. All isolates of P. palmivora from olive were of the A1 mating type. The pathogenicity of four P. palmivora isolates from olive, two producing only typical and two producing both types of sporangia, was tested in the greenhouse at 18 to 25°C, using 20 1-year-old rooted cuttings of olive cv. Carolea for each isolate. Twenty noninoculated cuttings were used as a control. The inoculum for pathogenicity tests was produced on autoclaved rice grains moistened with V-8 juice. Cuttings were transplanted to pots filled with soil infested with inoculum at 2% (wt/vol). Control plants were grown in pots containing a mixture of soil and 2% autoclaved rice. After transplanting, all pots were flooded once a week for 24 h by plugging the drain hole of the pot. One month after planting, all the plants in infested soil had died and no difference in virulence was observed among the isolates. Control plants remained healthy. P. palmivora was reisolated from the roots of symptomatic plants. Pathogenicity tests were repeated twice with similar results. In a survey of nurseries in Southern Italy, P. palmivora was recorded frequently from roots of young olive trees suggesting that infections originated from nurseries. This is the first report from Italy of P. palmivora on olive. This species has been described recently as a pathogen of olive in Spain (3). References: (1) D. C. Erwin and O. K. Ribeiro. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society. St. Paul, MN. (2) H. Masago et al. Phytopathology 67:25, 1977. (3) M. E. Sanchez Hernandez et al. Eur. J. Plant Pathol. 104:347, 1998.