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Ecology and Epidemiology

Isolation and Localization of the Antibiotic Gliotoxin Produced by Gliocladium virens from Alginate Prill in Soil and Soilless Media. R. D. Lumsden, Biocontrol of Plant Diseases Laboratory, Plant Sciences Institute, U.S. Department of Agriculture, Agricultural Research Service, Beltsville, MD 20705-2350; J. C. Locke(2), S. T. Adkins(3), J. F. Walter(4), and C. J. Ridout(5). (2)(3)Florist and Nursery Crops Laboratory, Plant Sciences Institute, U.S. Department of Agriculture, Agricultural Research Service, Beltsville, MD 20705-2350; (4)W. R. Grace & Co.-Conn., Columbia, MD 21044; (5)Biocontrol of Plant Diseases Laboratory, Plant Sciences Institute, U.S. Department of Agriculture, Agricultural Research Service, Beltsville, MD 20705-2350; (3)Current address: Department of Plant Pathology, University of Wisconsin, Madison, WI. Phytopathology 82:230-235. Accepted for publication 2 October 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992. DOI: 10.1094/Phyto-82-230.

Gliocladium virens produced detectable levels of gliotoxin when grown with an alginate-wheat bran food base delivery system in peat moss-vermiculite soilless medium (PV medium). The fungus also effectively controlled damping-off of zinnia seedlings caused by Pythium ultimum and Rhizoctonia solani in this same system. Gliotoxin was not detectable, and biocontrol effectiveness was greatly reduced when the fungus was grown in a medium containing bark ash (charcoal). Aqueous extracts obtained from PV medium amended with G. virens when drenched onto planted flats were as effective for control of damping-off of zinnias as the intact G. virens-amended PV medium. Gliotoxin was detected in PV medium (0.42 g/cm3), composted mineral soil (0.36 g/cm3), clay soil (0.20 g/cm3), and sandy soil (0.02 g/cm3), all with natural microbiota but amended with 0.1% alginate prill containing G. virens (w/v). At a rate of 0.4% amendment, the amount of gliotoxin detected was quadrupled when compared to the 0.1% rate. Damping-off caused by P. ultimum was significantly suppressed by prill of G. virens in PV medium, composted mineral soil, and clay soil, but not in sandy soil. Gliotoxin was detected 45 cm away from the point source of G. virens growing from a single bran-alginate prill in PV medium and appeared to be associated with the mycelium of the advancing margins of the colony. In a concentrated mixture of soilless mix and nonsterile G. virens prill (1:1, v/v), gliotoxin was detected at high levels (up to 0.65 mg/g of prill) after 1 day of incubation but not at zero time. The amount of gliotoxin diminished with time but was still detectable after 18 days of incubation (<0.1 mg/g of prill). Gliotoxin was detectable over a wide range of incubation temperatures (1530 C) in PV medium amended with prill of G. virens. After 3 days of incubation, detectable amounts were present at 15 C, but maximum production occurred at 30 C. These results show that gliotoxin can be detected in soils and soilless media and is correlated with disease suppressive activity toward P. ultimum and R. solani in nonsterile growing media. Factors such as time and temperature, and possibly organic matter, nutrient status, and other chemical and physical factors affect the ability and capacity of G. virens to produce gliotoxin.