First Report of Fusarium Wilt of Alfalfa in Greece

Abstract

In August 2000, samples of alfalfa (Medicago sativa L.) plants cv. Iliki showing wilt symptoms consistent with those reported for Fusarium wilt (1) were collected from an alfalfa field of the Agricultural University of Athens. Symptoms of the disease were chlorosis, yellowing, premature defoliation, wilting, vascular discoloration (dark brown), stunting, and death of plants. Fusarium oxysporum was isolated from the stems of diseased plants. Fresh cultures of the isolated fungus on potato dextrose agar (PDA) media developed whitish purple mycelium, short phialides, microconidia, and later, macroconidia and chlamydospores matching the description of F. oxysporum Schlechtend.:Fr. f. sp. medicaginis (Weimer) W.C. Snyder & H.N. Hans. (2). The fungus was maintained on PDA cultures at 4°C. Pathogenicity tests were conducted in a greenhouse (12-h photoperiod at 25 to 32°C) on alfalfa Greek cv. Iliki. An aqueous suspension of 107 microconidia per ml was prepared, and roots of 7-week-old seedlings were dipped for 20 min and then returned to pots. Within 15 days, all inoculated plants exhibited typical Fusarium wilt symptoms similar to those observed in the field. Four weeks after inoculation, almost all plants were dead. Control seedlings (root-dipped for 20 min in sterile distilled water) remained healthy. The fungus was reisolated from the symptomatic seedlings, fulfilling Koch's postulates. Weimer (3) first described Fusarium wilt of alfalfa and identified the causal organism as Fusarium oxysporum f. sp. medicaginis. Cross-artificial inoculation to cotton plants cv. Myrto, Christina, and Acala CJ2 was also performed, but none of the cultivars developed any macroscopic symptoms of the disease. To our knowledge, this is the first report of alfalfa Fusarium wilt in Greece. Although the pathogen was located in a rather isolated spot of alfalfa cultivation in Attica County, the occurrence of the pathogen and its importance in other alfalfa growing regions of Greece will be investigated. References: (1) D. C. Erwin. Fusarium wilt. Pages 33–34 in: Compendium of Alfalfa Diseases. 2nd ed. D. L. Stuteville and D. C. Erwin eds. The American Phytopathological Society, St. Paul, MN, 1990. (2) W. C. Snyder and H. N. Hansen. Am. J. Bot. 27:64, 1940. (3) J. L. Weimer. J. Agric. Res. 37:419, 1928.