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Reduction of Fusarium Wilt of Carnation with Suppressive Soils and Antagonistic Bacteria. G. Y. Yuen, Former Research Assistant, Department of Plant Pathology, University of California, Berkeley 94720. M. N. Schroth, Professor, and A. H. McCain, Extension Plant Pathologist, Department of Plant Pathology, University of California, Berkeley 94720. Plant Dis. 69:1071-1075. Accepted for publication 17 May 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-1071.

Severity of Fusarium wilt caused by Fusarium oxysporum f. sp. dianthi in greenhouse-grown carnations was reduced 1866% for 90 days when two wilt-suppressive soils were incorporated into an infested wilt-conducive soil mix at a rate of 1% (v/v). Preplant treatment of carnation cuttings by dipping roots in a slurry of suppressive soil resulted in 68 and 35% reductions in disease severity at 50 and 90 days, respectively. Application of an unsterile filtrate of a suppressive soil slurry was comparable in reducing disease severity to the incorporation of suppressive soil into conducive soil at rates of 1 and 10%. Ten soils from the Salinas Valley, when applied to rooted cuttings as slurries, reduced wilt severity by amounts ranging from about 25% to more than 75% at 5 mo. Alcaligenes sp. MFA1 and Pseudomonas putida C88, both isolated from the roots of carnations grown in a suppressive soil, significantly reduced wilt severity by 40 and 30%, respectively, for about 75 days in repeated experiments. Bacillus subtilis A13 and Pseudomonas sp. B10, strains previously tested for plant growth promotion in greenhouse and field trials, gave similar levels of disease control. Treatments with specific bacteria, however, were not as effective in reducing Fusarium wilt as treatments with suppressive soil slurries for intervals of 120 days. Survival of strain MFA1 on the root system of carnation was influenced by the texture and pH of the soil in which the plant was grown. The root population densities of MFA1 detected over a 5-mo period were lower in sand and loamy sand soils with low pH than in sandy loam and clay loam soils with near-neutral pH. In evaluations of suppressive soil and specific bacteria for control of Fusarium wilt of carnations grown in commercial greenhouse beds, only the suppressive soil significantly reduced disease incidence.

Keyword(s): biological control, Dianthus caryophyllus, root colonization.