Race 1,2y of Fusarium oxysporum f. sp. melonis on Muskmelon in Sicily.

Muskmelon (Cucumis melo L.) is very important economically to agriculture in Italy. The Sicily area accounts for ≈40% of the total muskmelon production. Fusarium wilt caused by Fusarium oxysporum f. sp. melonis (Leach & Currence) W.C. Snyder & H.N. Hans. is the most prevalent and damaging disease of muskmelon in Sicily. Use of cultivars with major resistance genes, Fom 1 and Fom 2, is the most effective control measure for combating the disease. During March 1999, severe infections of Fusarium wilt were noted in a commercial muskmelon crop, cv. Firmo F1, grown in plastic tunnels in Syracuse Province (eastern Sicily). The muskmelon seedlings had been transplanted into the tunnels during January 20 days after soil fumigation with methyl bromide. Firmo F1 possesses both Fom 1 and Fom 2 genes. Of 18,000 Firmo F1 plants, ≈6,500 showed symptoms consisting of stunting, vein clearing; leaf yellowing, wilting, and dying; brown necrotic streak; and gummy exudates on the basal portion of vines. A pinkish white mold developed on dead tissues when infected plants were kept at high relative humidity. The pathogenicity of both a single-conidium isolate of F. oxysporum f. sp. melonis from a symptomatic Firmo F1 plant and two isolates of races 0 and 1, recovered previously from other cultivars in Sicily and used as references, was tested with three differential muskmelon cultivars, Charentais T, Doublon, and CM 17187 (1), as well as three commercial cultivars, Ramon, Cassella, and Geamar (possessing Fom 1, Fom 2, and both Fom 1 and Fom 2 resistance genes, respectively). Muskmelon seedlings were inoculated by the root-dip method (3), using a suspension of 5 × 10 conidia per ml. Inoculated seedlings were transplanted to plastic pots filled with sterilized soil and placed in a greenhouse (25 to 30°C). Symptoms were scored 7 to 10 days after inoculation. The isolate from Firmo F1 was pathogenic to all cultivars tested, the race 0 isolate was pathogenic only to cv. Charentais T, and the race 1 isolate was pathogenic only to cvs. Charentais T, Doublon, and Ramon. F. oxysporum was reisolated from symptomatic plants. Based on its pathogenicity and symptomology, the isolate from Firmo F1 was classified as race 1,2y (yellows), according to the nomenclature proposed by Risser et al. (1). Race 1,2 poses a serious threat to muskmelon production in Sicily, because all currently used cultivars are susceptible to the race, and other control measures, such as preplant soil fumigation with methyl bromide and solarization, are not as effective as use of resistant cultivars. Further study is needed to establish which is the prevalent race of F. oxysporum f. sp. melonis in Sicily. This report confirms that race 1,2 occurs in all major muskmelon-production areas in Italy (2). References: (1) G. Risser et al. Phytopathology 66:1105, 1976. (2) G. Tamietti et al. Petria 4:103, 1994. (3) F. L. Wellman. Phytopathology 29:945, 1939.