Biological control of Fusarium wilt of carnation with a nonpathogenic isolate of Fusarium oxysporum

The nonpathogenic isolate 618-12 of Fusarium oxysporum, wild type as well as a benomyl-resistant mutant, suppressed Fusarium wilt (F. o. f.sp. dianthi) in a susceptible cultivar of carnation by 80%. Two other nonpathogenic isolates had a similar effect. Suppression by isolate 618-12 occurred only when antagonist and pathogen were both added to the soil but not if they were introduced at a different location (one in the stem, the other in the soil). Thus systemic induced resistance could not be demonstrated. In treatments where isolate 618-12 and the pathogen were both introduced into the soil, fewer plants showed symptoms, disease severity was less, and colonization by the pathogen was less extensive than after inoculation with the pathogen alone. After soil inoculation, the nonpathogenic isolate 618-12 was recovered from the stem, sometimes at a height of 60 cm. Key words: colonization, carnation stem, soil.