spp. isolated from soils collected from Kabete, Department of Crop Science, University of Nairobi isolates were screened for antibiosis against Fusarium oxysporum
f. sp. dianthi in vitro
. The culture filtrate of isolate 21, one of the antagonistic isolates was tested for activity and found to suppress growth of F. oxysporum
f.sp dianthi in vitro
. The culture filtrate was used to treat pathogen inoculated carnation cuttings and it reduced stem discolouration by 62.2% which was comparable to reduction by benlate that reduced stem discolouration by 78.3%. Different concentration levels of the culture filtrate (concentrated filtrate, normal filtrate, half strength filtrate and quarter strength filtrate) all effectively reduced discolouration of the carnation stems by 93.3, 73.1, 68.5 and 63.4%, respectively. Phytotoxicity that led to chlorosis and partial wilting during the first week of treatment was detected in the antibiotic treated plants especially when applied to young and tender cuttings. The chlorosis and partial wilting were significantly reduced when older and well established cuttings were used and when the culture filtrate was diluted to half or quarter strength.