1e:T4aa,Nonpathogenic Fusarium oxysporum Fo47b10 combined with Pseudomonas putida WCS358 efficiently suppressed fusarium wilt of carnations grown in soilless culture. This suppression was significantly higher than that obtained by inoculation of either antagonistic microorganism alone. The increased suppression obtained by Fo47b10 combined with WCS358 only occurred when Fo47b10 was introduced at a density high enough (at least 10 times higher than that of the pathogen) to be efficient on its own. P. putida WCS358 had no effect on disease severity when inoculated on its own but significantly improved the control achieved with nonpathogenic F. oxysporum Fo47b10. In contrast, a siderophore-negative mutant of WCS358 had no effect on disease severity even in the presence of Fo47b10. Since the densities of both bacterial strains at the root level were similar, the difference between the wild-type WCS358 and the siderophore-negative mutant with regard to the control of fusarium wilt was related to the production of pseudobactin 358. The production of pseudobactin 358 appeared to be responsible for the increased suppression by Fo47b10 combined with WCS358 relative to that with Fo47b10 alone.1f:T50d,Metz fine sandy loam soil from the Salinas Valley in California was suppressive to the Fusarium spp. which induce wilts of flax and carnation. Suppressiveness to Fusarium oxysporum f. sp. dianthi was transferred to conducive soil when the Metz fine sandy loam was added in small amounts to steamed greenhouse soil. Aerated steam treatment of the suppressive soil at 54 C for 30 min eliminated the suppressive effect. Lowering of pH values of the Metz fine sandy loam from 8.0 to 6.0 in unit increments eliminated the suppressive effect. Bacteria were isolated from mycelial mats of F. oxysporum f. sp. lini buried in the suppressive soil and conducive soils. Two isolates from suppressive soil introduced into conducive soil at 10⁵ cells per gram of soil significantly reduced disease incidence of Fusarium wilt of flax. The more effective of these isolates inducing suppressiveness was a Pseudomonas sp. Viability of this organism was drastically reduced when soil was treated with aerated steam at 54 C. These results suggest that suppressiveness in the Metz fine sandy loam is biological in origin and that control of Fusarium wilt diseases may be accomplished through introduction of appropriate species of bacteria into conducive soil.20:T65b,

	Year	Citations

References