December 8, 2004
Source: American Phytopathological Society, Plant Disease Notes [edited]

Detection of Fusarium oxysporum f. sp. melonis Race 1 in soil in Colima State, Mexico
M. de Cara, E. J. Fernandez, R. Blanco, and J. C. Tello Marquina, Universidad de Almeria, Departamento de Produccion Vegetal. La Canada de San Urbano s/n. 04120 Almeria, Spain; and F. J. Estrada and S. Montoya,
Universidad Autonoma de Sinaloa, Facultad de Agronomia, Culiacan, Sinaloa, Mexico. Plant Dis. 88:1383, 2004; published on-line as D-2004-0922-02N, 2004. Accepted for publication 6 Sep 2004.

During the winters of 2002 and 2003, a wilt occurred in melons cultivated on 1500 ha in Colima State, Mexico. Yield losses reached 25 percent of final production, despite soil disinfestation with 60 percent methyl bromide and 40 percent chloropicrin. On the basis of the observation of plants with necrotic xylem, yellowing, and wilting of leaves, this disease was identified provisionally as Fusarium wilt.

During February 2003, 4 soil samples from affected fields were plated onto a Fusarium-selective medium (1), which resulted in the detection of 2260 ± 357, 179 ± 76, 668 ± 357, and 1391 ± 256 CFU/g of _F. oxysporum_ (3). 31 randomly chosen isolates were used to inoculate differential cultivars of melon as described by Risser et al. (4). The cultivars were Amarillo Canario (susceptible to all races), Diana (resistant to races 0 and 2), Tango (resistant to races 0 and 1), and Vulcano (resistant to races 0, 1, and 2) (2).

10 plants of each cultivar, grown on sterilized vermiculite, were inoculated at the 1st true-leaf stage by drenching with 200 ml of a conidial suspension (100 000 CFU/ml) of each isolate. Noninoculated plants of each cultivar served as controls. Plants were maintained in a growth chamber with a 16-h photoperiod (18 × 1000 lux) and temperatures at 23 to 25 deg C.

Yellowing, wilt, and vascular discoloration symptoms developed on cvs. Amarillo Canario and Diana following inoculation with each of the 31 isolates, while noninoculated plants remained symptomless. _F. oxysporum_
was consistently reisolated on potato dextrose agar from the affected plants. On the basis of the combination of affected cultivars, all isolates were identified as _F. oxysporum_ f. sp. _melonis_ race 1.

To our knowledge, this is the 1st report of _F. oxysporum_ f. sp. _melonis_ race 1 in Colima State, Mexico.

References:

(1) H. Komada. Rev. Plant Prot. Res. 8:114, 1975.
(2) J. Marrn Rodriquez. Portagrano 2004. Vadmecum de Variedades Horticolas. Agrobook, Spain. 2004.
(3) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University Press, University Park, 1983.
(4) G. Risser et al. Phytopathology 66:1105, 1976.

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ProMED-mail
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[_F. oxysporum_ f. sp. _melonis_ (Fom) causes a severe disease of melon (muskmelon and canteloupe) in many parts of the world. There are 4 races, 0, 1, 2 and 1,2. Disease management is predicated on the use of resistant
cultivars, which in turn depends on fungal populations in the soil and the races present. Movement of farm equipment from Fom-infested fields to clean fields is to be avoided because chlamydospores remain viable for years. In addition Fom can be spread on tools, feet and in surface water contaminated with infested soil. Deposition of compost on clean fields is to be avoided since it contains Fom. Crop rotation can be helpful in lowering the amount of Fusarium in the soil, as part of an integrated management program using resistant varieties. It is important to rotate to unsusceptible plant species, such as grasses or cereals.

I am puzzled by the emphasis on race 1. What is the effect of this race on melon compared to races 0, 2 and 1,2? Perhaps our readers can enlighten me on this point.

Links:
<http://www.avrdc.org/LC/cucurbits/fusarium.html>
<http://www.dpi.qld.gov.au/horticulture/11645.html>
<http://www.agr.unipi.it/sipav/jpp/journals/meet1999.htm>
<http://www.blackwell-synergy.com/links/doi/10.1046/j.1365-3059.2003.00806.x/abs/> 
- Mod.DH]