Zucchini plant collapse has been often associated with Fusarium solani f. sp. cucurbitae race 1, which is the causal agent of Fusarium crown and foot rot disease of cucurbits. In Italy, F. solani f. sp. cucurbitae race 1 has been reported on zucchini (Cucurbita pepo) in a greenhouse in the Tuscany Region (4). In spring 2005, a severe outbreak was observed on zucchini in a vast area of cultivation in the province of Venice. Isolations from necrotic vessels gave more than 20 single-spore cultures. On the basis of morphological characteristics, they were identified as F. solani (2) and Plectosporium tabacinum (3). The internal transcribed spacer (ITS) region of rDNA was amplified and sequenced. A fragment of 454 and 531 bp was 99% homologous with sequence PSU66732 and AF150472 of F. solani f. sp. cucurbitae race 1 and P. tabacinum, respectively, in the NCBI database. The nucleotide sequences have been assigned Accession No. AM408782 for F. solani f. sp. cucurbitae race 1 and AM408781 for P. tabacinum. Pathogenicity tests were conducted with four isolates of each species on 15-day-old zucchini plants and on fruit. Plants were inoculated by dipping the roots in a conidial suspension of 106 spores ml-1 for 10 min. Control plants were dipped in sterile water. Five replicates for the inoculated and control plants were used. All plants were maintained in a greenhouse at approximately 24°C. After 14 days, inoculations with F. solani f. sp. cucurbitae race 1 gave symptoms of a cortical rot at the base of the stem with a progressive yellows and wilting of leaves, while plants inoculated with P. tabacinum displayed a moderate wilting. Fruit were washed under running water, disinfected with a solution of 3% sodium hypochlorite and 5% ethanol for 1 min, and inoculated with 6-mm-diameter mycelial plugs cut from the margin of 10-day-old cultures grown on PDA. Plugs were inserted into holes (approximately 2 mm deep) made with a sterile 7-mm-diameter cork borer. Five replicates per isolate were used. Fruit were kept at room temperature (22 to 24°C) in a moist chamber. All isolates induced symptoms of fruit rotting 10 days after inoculation. All controls remained healthy. The colonies reisolated from the inoculated plants and fruit were morphologically identical to the original isolates. The results obtained proved that F. solani f. sp. cucurbitae race 1 can be considered the major pathogen in zucchini collapse, at the same time P. tabacinum may play a role in this syndrome as reported for other cucurbits (1). To our knowledge, this is the first report of zucchini plant collapse caused by F. solani f. sp. cucurbitae race 1 and P. tabacinum, and the first report of P. tabacinum on zucchini in Italy.
References: (1) V. J. Garcia-Jimenez et al. EPPO Bull. 30:169, 2000. (2) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University, University Park, 1983. (3) M. E. Palm et al. Mycologia 87:397, 1995. (4) G. Vannacci and P. Gambogi. Phytopathol. Mediterr. 19:103, 1980.
