Nature of Suppression of Fusarium Wilt of Radish in a Container Medium Amended with Composted Hardwood Bark. M. I. Trillas-Gay, Former Graduate Student, Department of Plant Pathology, Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. H. A. J. Hoitink, Professor, and L. V. Madden, Associate Professor, Department of Plant Pathology, Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. Plant Dis. 70:1023-1027. Accepted for publication 11 June 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-1023.

The suppressive effect of a container medium amended with composted hardwood bark (CHB) to Fusarium oxysporum f. sp. conglutinans race 2 (F. o. f. sp. conglutinans) was biotic in nature. Heating destroyed the suppressive effect. Population development of F. o. f. sp. conglutinans was suppressed in the unheated but not in the heated CHB medium. A combination antagonist treatment consisting of strains of Trichoderma hamatum and an isolate of Flavobacterium balustinum consistently restored the suppressive effect in heated media. Neither antagonist type added singly was consistently effective. The CHB medium was suppressive over a wide pH range (5.4–7.4). Ammonium nitrate nitrogen did not have a significant effect on disease severity, but calcium nitrate and ammonium sulfate nitrogen did.