April 8, 2005
Source: J. Phytopathology, Vol. 153 [edited]

Detection of races 1 and 2 of Fusarium solani f. sp. cucurbitae and their distribution in watermelon fields in Tunisia
N. Boughalleb, Ecole Superieure d'Horticulture et d'Elevage, Chott Mariem 4042, Sousse, Tunisia; J. Armengol, Instituto Agroforestal Mediterraneo, Universidad Politecnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain; and M. El Mahjoub (as for Boughalleb). Received 6 Aug 2004; accepted 18 Jan 2005.

A crown, foot and fruit rot of watermelon has been observed in most of the watermelon production areas in Tunisia. A survey conducted from 2000 to 2001 allowed the isolation of 291 isolates which were identified as
_Fusarium solani_. These isolates were identified as _F. solani_ f. sp._cucurbitae_ (Fsc) and races 1 and 2 characterized on the basis of pathogenicity tests on watermelon seedlings and muskmelon fruits. These
results were confirmed by counts of the number of septa in the macroconidia. About 271 isolates were identified as Fsc race 1, 12 isolates were identified as Fsc race 2 and 8 isolates were not pathogenic.

Race 1 is widely distributed in watermelon production areas in Tunisia and race 2 has a lower incidence, but it is present in the north, the middle and southern Tunisian watermelon cropping areas. Additionally, a study to
compare the virulence of 122 isolates of Fsc race 1 showed different degrees of virulence among them.

This is the 1st report of Fsc races 1 and 2 in Tunisia.

--
ProMED-mail <promed@promedmail.org>

[Fsc causes necrotic lesions affecting the stem near the ground, eventually resulting in girdling of the stem. Plants become wilted and die rapidly during mid-season. The decay at the base of the stem is soft and mushy.
Fruit lesions begin as small corky cracks that develop into sunken necrotic lesions. Internal tissue near the site of infection becomes off-color and corky. Fruit decay results in a firm, dry rot. A PCR-based technique has been devised to determine genome variability between Fsc isolates of Fsc isolates races 1 and 2. Fusarium crown and foot rot occurs sporadically in most areas, and disease severity is dependent on soil moisture and inoculum
density.

Because the fungus survives in the soil for only 2-3 years, a 4-year rotation is usually adequate for disease control. Planting fungicide-treated seed is also effective in reducing the incidence of disease initiated from infected seed. Additional measures would include use of resistant or tolerant cultivars if available and cleaning of farm machinery and tools so as to prevent soil-borne spread of the pathogen. A PCR-based technique has been devised to determine genome variability between Fsc isolates of races 1 and 2.

Links:
<http://www.apsnet.org/online/feature/pumpkin/fuscrown.html>
<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1807830&dopt=Abstract>
<http://aggie-horticulture.tamu.edu/cucurbit/fruit/15.2.html>
- Mod.DH]