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First Report of Nectria haematococca Causing Wilt of Olive Plants in Argentina

Death of 8- to 12-month-old olive plants (Olea europaea L. ‘Arbequina’, ‘Arauco’, and ‘Picual’) has been observed since 1998 in northwestern Argentina. No mycelium or perithecium was observed when examining rotting roots of greenhouse-collected plants. Root segments of diseased plants were plated on potato dextrose agar. Cultures developed a white mycelium after 2 to 3 days, producing microconidia, macroconidia, and chlamydospores identified as Fusarium solani (1). After 15 days of incubation at 23 ± 2°C, reddish perithecia developed infrequently on root segments and adjacent substratum. Single-septate ascospores were hyaline and turned light brown with longitudinal striations at maturity. Microscopic measurements agreed with Nectria haematococca (1). To conduct Koch's postulates (two experiments, two treatments including inoculated and controls, 10 replicates per treatment), young rooted cuttings (6- to 12-month-old) were transferred to pots with a soilless mix and F. solani-colonized oat grains (10:1 vol/vol) and placed in growth chamber (25 to 28°C). First symptoms of the disease were leaf drooping and apex bending after 5 days. At approximately 9 days, leaves turned brownish, developed wilting from the tip downward, and plant death. Controls remained healthy. The fungus was reisolated, and perithecia of N. haematococca developed. F. solani has been reported causing wilt and sudden death in olive previously (2,3). To our knowledge, this is the first report of perithecial development associated with F. solani on olive.

References: (1) C. Booth. The Genus Fusarium. CAB International, Wallingford, UK, 1971. (2) R. L. Munjal et al. Studies on diseases of olive in himachal pradesh. Pages 437--440 In: Improvement of Forest Biomass. Symposium Proceedings. Indian Society of Tree Scientists. P. K. Kosla, ed. Sdan, India, 1982. (3) B. A. Pérez et al. (Abstr.) Phytopathology 91 (suppl):S71, 2001.