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First Report of Basal Rot of Leek Caused by Fusarium culmorum in Spain

A severe basal rot of leek (Allium porrum L.) was first observed in 1996 in Sueca (Valencia) eastern Spain, and again from 1998 to 2000 in several fields in Haro (La Rioja) northern Spain, where the disease caused significant economic losses. Leeks were stunted, wilted, and had water-soaked tissues with a characteristic reddish purple discoloration at the base of the stem. Affected plants could be pulled up easily because of rotting of the basal plate and root system. Similar symptoms were also observed on seedlings 2 to 3 weeks after transplanting. Isolations from symptomatic stems and roots onto potato dextrose agar (PDA) supplemented with 0.5 mg/ml of streptomycin sulfate (PDAS) consistently yielded a Fusarium sp. Isolates were transferred to potato sucrose agar (PSA) and synthetic low nutrient agar (SNA) and incubated at 25°C for 10 days with a 12-h photoperiod. The isolates were identified as Fusarium culmorum (Wm. G. Sm.) Sacc. based on colony morphology on PSA and phialide and conidial morphology on SNA. This disease has been described on garlic (1), but there are few reports about its incidence on leek (2). Pathogenicity tests were conducted on leek cvs. Alora, Axel, Casado, Goliath, and Varea using five isolates of F. culmorum from different locations. Ninety-day-old seedlings were inoculated by introducing a spore suspension to obtain a soil infested with the fungus at 10⁴ colony-forming units (CFU)/g of potting mix (a sterilized mixture of equal portions [v/v] of soil, sand, and peat moss). Plants were maintained in a greenhouse at 20 to 30°C. Within 45 to 70 days after inoculation, symptoms developed that were similar to those observed in the field. The fungus was reisolated from affected plants, completing Koch's postulates. All isolates were pathogenic, and all leek cvs. were highly susceptible to the pathogen. To our knowledge, this is the first report of F. culmorum affecting leek in Spain.

References: (1) F. J. Crowe et al. Phytopathology 76:1094, 1986. (2) G. Tamietti and A. Garibaldi. Riv. di Patol. Veg. IV. 13:69, 1977.