August 15, 2005
From: ProMED-mail <promed@promedmail.org>
Source: American Phytopathological Society, Plant Disease Notes [edited]

First demonstration of Koch's postulates for Lasiodiplodia theobromae fruit spot on eggplant
J. E. Woodward, D. B. Langston, Jr., J. H. Brock, R. C. Kemerait, Jr., and T. B. Brenneman, Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793; and G. H. Beard, University
of Georgia Cooperative Extension Service, Moultrie 31768. Plant Dis. 89:687, 2005; published on-line as DOI: 10.1094/PD-89-0687A. Accepted for publication 10 Mar 2005.

During October 2004, diseased eggplant fruit from a commercial farm in Colquitt County, Georgia, developed circular, tan, water-soaked lesions. Gray, septate mycelia quickly covered the fruit. Diseased fruit became shriveled, spongy, and mummified. Disease incidence in the field was approximately 1 percent.

_Lasiodiplodia theobromae_ (Pat.) Griffon & Maubl. (synonym _Botryodiplodia theobromae_ Pat.) (2) was isolated from the margins of lesions and cultured on acidified potato dextrose agar. The fungus produced grayish colonies
with aerial hyphae and black ostiolate pycnidia massed into stroma. Mature elliptical conidia (25.8 x 15.6 micrometers) were brown, had a single septation, and longitudinal striations. Isolates obtained from peanut and
pecan were included in the pathogenicity tests. Mature fruit cv. Nightshade were surface disinfested for 30 s in 70 percent ethanol, followed by 60 s in 0.5 percent sodium hypochlorite, rinsed twice in sterile distilled water, and allowed to dry.

Inoculations were made by placing an agar plug containing _L. theobromae_ mycelial side down on the surface of the fruit or wounding with a sterile toothpick containing mycelium of the fungus. Fruit similarly inoculated with agar plugs or sterile toothpicks served as controls. There were a total of 3 replicates. Fruit were placed in plastic containers lined with moistened paper towels. Containers were placed in a dew chamber and incubated (28 C, relative humidity >95 percent) for 3 days, and then evaluated.

Symptoms identical to those observed on naturally infected fruit developed on inoculated fruit. Controls remained disease free. _L. theobromae_ was reisolated from all symptomatic tissue, satisfying Koch's postulates. Disease damage on wounded fruit was twice that of nonwounded fruit. However, 7 of 9 inoculations with agar plugs containing _L. theobromae_ resulted in infection. Lesion lengths from wound inoculations were 9.8, 7.3, and 5.2 cm for isolates from peanut, pecan, and eggplant, respectively. Generally, _L. theobromae_ is considered a facultative wound pathogen or a secondary invader (3). However, this study suggests that direct infection can occur.

Although fruit spot has been reported previously on eggplant (1), to our knowledge, this is the 1st report verifying _L. theobromae_ as the causal agent.

References:

(1) S. A. Alfieri et al. Index of Plant Diseases in Florida. Fla. Dep. Agric. Consum. Serv. Bull. 11, 1984.

(2) H. L. Barnett and B. B. Hunter. Illustrated Guide of Imperfect Fungi. 4th ed. The American Phytopathological Society St. Paul, MN, 1998.

(3) P. M. Phipps and D. M. Porter. Plant Dis. 82:1205, 1998

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[Basically this piece confirms that _L. theobromae_ is a pathogen that causes fruit spot on eggplant (_Solanum melongena _). Other fungal pathogens infecting eggplant are a leaf and fruit spot caused by _Phoma_ sp., leaf spot caused by _Cercospora melongenae_ and fruit rot caused by _Rhizopus stolonifer_). - Mod.DH]