April 18, 2005
Source: American Phytopathological Society, Plant Disease Notes [edited]

First report of gray mold in tomato caused by Botrytis cinerea in Baja California, Mexico
RJ Holguin-Pena, FG Arcos, Centro de Investigaciones Biologicas del Noroeste, Mar Bermejo No. 195, Col. Playa Palo de Santa Rita. AP 128, La Paz, BCS 23090, Mexico. Plant Dis 2005; 89: 528, published online as DOI: 10.1094/PD-89-0528B. Accepted for publication 1 Feb 2005.

San Quintin Valley, a 60 mile long coastal plain (30 deg 30 min N, 116 degW) in the Baja California Peninsula, is one of the major fresh tomato (_Lycopersicon esculentum_ Mill.) production areas in Mexico with more than
8000 ha.

In the past 10 years, the valley's tomato production has declined because of gray mold and stem canker diseases. Flower rot, reddish brown margins on the leaves and stems, and fruit with a gray mold were observed on field-grown tomato plants (Roma type cv. Tequila) in the autumn of 2003. Severity ranging from 55 to 60 per cent was observed at harvest.

Infected tissues were sampled and disinfested by immersion in 1 per cent NaOCl for 1 min, rinsed in sterile water, and placed on malt extract agar at 22 deg C. Fungal conidia were then transferred to 2 per cent potato dextrose agar (PDA). The resulting fungal colonies were definitively identified as _Botrytis cinerea_ Pers.:Fr.

The colonies of _B. cinerea_ were first hyaline and white and became dark gray after 96 h. Mycelia were septate with dark branched conidiophores. Conidia were unicellular, ellipsoid, and ranged from 5 to 8 -- 8 to 14 micrometers. Profuse black sclerotia developed in 7 day old cultures. Infection site analyses in diseased flowers at different stages during the bloom were done with scanning electron microscopy. Fungal hyphae were located predominantly on the receptacle areas, whereas conidia were located in the ovaries as described previously (1).

The identity of _B. cinerea_ was confirmed by a restriction digest with ApoI of the 413-kb polymerase chain reaction amplification product obtained with BA2f/BA1r primers (2) and random amplified polymorphic DNA banding patterns (3).

Pathogenicity tests were done by spray inoculation of 1 ml aqueous conidial suspension (1 million CFU/ml) on 20 healthy plants during the blossom stage. An equal number of plants sprayed with sterile water was used as the
control. Plants were incubated at 20 ± 2 deg C for 5 days.

The fungus was reisolated from diseased flowers and peduncles after surface disinfestation (2.5 per cent NaOCl) and plating on PDA. No symptoms were observed in the noninoculated controls.

To our knowledge, this is the 1st report of _B. cinerea_ causing gray mold disease on tomato in Baja California.

References:
1. O Viret, et al. Phytopathology 2004; 94: 850.
2. K Nielsen, et al. Plant Dis 2002; 86: 682.
3. S Rigotti, et al. FEMS Microbiol Lett 2002; 209: 169.

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[I was surprised to note that Botrytis blight or gray mold [GM] has not been reported prior to this post, given its wide host range. GM is a fungus disease infecting many herbaceous annual and perennial crops. GM can be
particularly damaging under continuous rainy, drizzly weather conditions for several days. The host range of GM is extensive (asparagus, bean, beet, crucifers, cucurbits, eggplant, grape, lettuce, onion, pepper, potato,
tomato, turnip, and others). If cool, overcast conditions predominate, the disease progresses and a fuzzy grey mold develops. If conditions are warm and sunny, only ghost spots remain without any further disease progression. Cool, wet weather exacerbates disease expression. Fungicides can be used to prevent the spread of infection.

Links:
<http://plantclinic.cornell.edu/FactSheets/botrytis/botrytis_blight.htm>
<http://www.ipm.ucdavis.edu/PMG/r584100311.html>
<http://www.visionkbc.co.kr/study/rd5.htm>
<http://www.hort.uconn.edu/ipm/greenhs/htms/ghtmdp.htm>
<http://ipcm.wisc.edu/news/misc/tomfrtdis.htm> - Mod.DH]