July 10, 2003
Source: American Phytopathological Society, DISEASE NOTES [edited]

Buckeye Rot of Tomato Caused by _Phytophthora capsici_ in Michoacan, Mexico

S. P. Fernandez-Pavia and G. Rodriguez-Alvarado, Instituto de Investigaciones Agropecuarias y Forestales, Universidad Michoacana de San Nicolas de Hidalgo, Morelia, Michoacan 58240, Mexico; and J. M. Sanchez-Yanez, Instituto de Investigaciones Quimico-Biologicas, Universidad Michoacana de San Nicolas de Hidalgo, Morelia, Michoacan 58030, Mexico. Plant Dis. 87:872, 2003; published on-line as D-2003-0506-01N, 2003. Accepted for publication 23 Apr 2003.

The state of Michoacan is one of the main fresh pepper (_Capsicum annuum_ L.) and tomato (_Lycopersicon esculentum_ Mill.) producers in Mexico. During the last 5 years, pepper-producing areas in the state have become unproductive due to root-rotting pathogens, mainly _Phytophthora capsici_ Leonian. Growers trying to overcome losses have increased tomato production in areas previously used for pepper production.

Field-grown tomato plants with diseased green tomato fruits were observed in Tacambaro, Michoacan, during August 2002. Initially, brown-to-black lesions developed on fruits in contact with soil, followed by infection of the upper fruits in the raceme. Lesions enlarged and dark zonate "buckeye" bands were formed in the affected area. Disease fruit turned mushy. Symptoms observed were similar to those for buckeye rot of tomato (1).

Disease fruit were surface disinfested with 70 percent ethanol, cut into 0.5-cm slices, and incubated in a moist chamber to induce mycelial colonization. Isolation from mycelial tufts growing through the tomato
slice was performed 3 days later, and mycelia was transferred to PARP selective medium (corn meal agar (CMA) plus ampicillin, pimaricin, rifampcin, and pentachloronitrobenzene). _P.capsici_ was consistently
isolated from diseased tomato fruits.

Oomycete identification was based on sporangial and gametangial characteristics of cultures grown on CMA (1). Sporangia microscopically observed were spherical, broadly ellipsoid, or obovoid with 1 papilla
(occasionally 2 papillae), and deciduous with a long pedicel. Chlamydospores were not present (2). The isolates were heterothallic, and oogonia with amphigynous antheridia were observed in pairings with A1 and A2 isolates of _P. capsici_. 3 isolates were A1 and 2 isolates were A2.

To confirm pathogenicity, 2 experiments were performed using 20 healthy unwounded green tomatoes. 1 isolate of each mating type was tested. Isolates were grown for 5 days on CMA, and fruits were inoculated by placing _P. capsici_ in contact with the fruit. Inoculated fruits were kept in a moist chamber at room temperature (17 to 20 deg C). Initial symptoms in the form of brown-to-black lesions appeared 24 h after inoculation.

1 week after inoculation, symptoms were similar to those observed in field-grown plants, and _P. capsici_ was recovered from the margins of the diseased tissue. All inoculated fruits rotted.

To our knowledge, this is the first report of _P. capsici_ causing buckeye rot on tomato in Michoacan and of the presence of both mating types in the area.

References:
(1) D.C. Erwin and O.O. Ribeiro. _Phytophthora_ Diseases Worldwide. The American Phytopathological Society. St. Paul, MN.
(2) M. Aragaki and J.Y. Uchida. Mycologia 93:137, 2001.

[In addition to _P. capsici_, 2 other _Phytophthora_ species (_P. parisitica_ and _P. drechsleri_) have been implicated in causing buckeye rot. Other crops affected by these species include beans, corn, eggplant, melons, onions, pepper, potato, pumpkin, rhubarb, squash, and turnip. Disease development is favored by warm, wet weather. Management of the disease depends on use of phytosanitary measures, preventing tomato fruits from contacting soil, crop rotation, and application of chemical fungicides. Apparently there are no tomato cultivars that are resistant to _P. capsici_. - Mod.DH]