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First Report of Fusarium solani f. sp. cucurbitae Race 1 in Spain

A crown, root, and fruit rot of squash (Cucurbita maxima Duchesne) was first observed in 1995 and again in 1996 in several fields in the eastern provinces of Valencia and Castellón. When plants approach maturity they exhibited a severe cortical rot at the base of the stem and the upper portion of the taproot causing yellowing and wilting of the leaves. Within a few days of the first symptoms of crown rot, affected plants usually died. Soft, circular lesions developed where fruit were in contact with soil. Isolations on potato dextrose agar supplemented with 0.5 mg/ml of streptomycin sulfate (PDAS) from the crown of symptomatic plants and fruits yielded primarily a Fusarium sp. Isolates were transferred to potato sucrose agar (PSA) and Bilay's medium, modified by Joffe (SNA), and incubated at 25°C for 10 days with a 12-h photoperiod. The isolates were identified as Fusarium solani (Mart.) Sacc. based on colony morphology on PSA and fungal morphology on SNA. C. maxima (cv. Dulce de Horno) seedlings (eight replicates per isolate) grown on a sterilized mixture of equal portions (vol/vol) of soil, sand, and peat moss were inoculated at the first true leaf stage by introducing a 10-ml spore suspension (10⁶ spores per ml) at the base of plants. Symptoms appeared in 14 to 21 days as linear, coalescing, cortical lesions in the hypocotyl of inoculated plants and ultimately caused seedling death. There were no differences observed in the five isolates tested, regardless of origin. Mature fruits were inoculated by injecting spore suspension (10⁶ spores per ml) into the mesocarp. Within 14 to 21 days after inoculation, lesions developed similar to those observed in the field. Stem isolates were pathogenic on the fruit, and fruit isolates were pathogenic on stems. Reference isolates NRLL 22165 and NRRL 22449 for race 1, and NRRL 20545 and NRRL 22144 for race 2, provided by K. O'Donnell, were also tested as positive controls. Only race 1 isolates caused seedling death. In each study, the fungus was reisolated, confirming Koch's postulates. Based on these results and disease symptoms in the field, the fungus was classified as F. solani f. sp. cucurbitae W. C. Snyder & H. N. Hans race 1, which causes a root, stem, and fruit rot, whereas race 2 causes only a fruit rot (1). F. solani also was isolated from seeds removed from diseased fruits. This is the first report of the presence of F. solani f. sp. cucurbitae race 1 in Spain.

Reference: (1) T. A. Tousson and W. C. Snyder. Phytopathology 51:17, 1961.