December 18, 2004
Source: American Phytopathological Society, Plant Disease Notes [edited]

First report of Pythium tracheiphilum causing wilt and leaf blight on lettuce (Lactuca sativa) in Spain
A. J. Gonzalez, Laboratorio de Fitopatologia, SERIDA, Carretera de Oviedo s/n, 33300 Villaviciosa, Asturias. Spain; J. C. Tello, Departamento de Produccion Vegetal. Universidad de Almeria, 04120 Almeria, Spain; and M. L
Herrero, The Norwegian Crop Research Institute, Plant Protection Centre, N-1432 As, Norway. Plant Dis. 88:1382, 2004; published on-line as D-2004-1005-02N, 2004. Accepted for publication 17 Sep 2004.

Since 2002, a disease on lettuce plants (cv. Estibaliz) was observed in the field and in greenhouses in the Principality of Asturias in northern Spain. The disease was estimated to cause losses of 20 percent in field-grown
crops during the summer.

Plants with aboveground symptoms of wilt and necrosis and darkening of vessels and necrosis in the tap root were collected. On potato dextrose agar (PDA), a fungus was recovered and identified as _Pythium tracheiphilum_ according to the following characters: terminal or intercalary, globose or subglobose sporangia; zoospores formed in water; chlamydospores present in old cultures; smooth, globose, terminal, and intercalary oogonia; and smooth, globose oospores (2).

For pathogenicity tests, 2 isolates were each inoculated on 9 seedlings (3 true leaves) and 9 plants (6 to 8 true leaves) of lettuce (Batavia type) grown in peat. Inoculum was prepared by suspending mycelium of the isolate
collected from 2 PDA plates in 100 ml of distilled water with 10 ml poured around each plant. Control plants received distilled water only. Plants were maintained at 21 deg C and 80 percent relative humidity with a 12-h
photoperiod.

Symptoms were observed after 4 or 7 days for seedlings and plants, respectively. Within 20 days, 33 percent of the seedlings and plants died, and all surviving plants showed symptoms. Symptoms did not occur on the control plants. _P. tracheiphilum_ was reisolated from inoculated plants but not from the control plants.

This fungus has been described previously as a lettuce pathogen in France and Italy (1) but to our knowledge, this is the 1st report of _P. tracheiphilum_ infecting lettuce in Spain.

References:

(1) C. M. Messiaen et al. Enfermedades de las hortalizas, Mundi-prensa, Madrid. 1995.
(2) A. J. van der Plaats-Niterink. Stud Mycol. 21:1, 1981

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[Disease management of _P. tracheiphilum_ includes crop rotation (3 years)
and good drainage. In contained nursery operations, avoid contamination of
the nutrient solution with soil. Avoid allowing dirty hands or tools to
come in contact with the plants or nutrient solution. Ultraviolet
sanitizing units for water are effective in destroying _Pythium_ spp. and
are available for installation into hydroponic operations. However, these
systems are of little value if the disease-causing organism is present in
the nutrient troughs and substrate.

Links:
<http://myweb.cableone.net/tfcox/diseases.htm#Wilts>
<http://www.ismpminet.org/resources/common/names/lettuce.asp>
<http://www.umassvegetable.org/soil_crop_pest_mgt/disease_mgt/mgt_hyrdo_grown/> 
- Mod.DH]