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Disease Control and Pest Management

Protection of Carnation Against Fusarium Stem Rot by Fungi. Ralph Baker, Professor, Botany and Plant Pathology Department, Colorado State University, Fort Collins, CO 80523; Penelope Hanchey(2), and Susan D. Dottarar(3). (2)(3)Associate Professor, and Research Assistant, respectively, Botany and Plant Pathology Department, Colorado State University, Fort Collins, CO 80523. Phytopathology 68:1495-1501. Accepted for publication 17 May 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1495.

Many species of fungi protected wounded carnation stem tissue from ingress by Fusarium roseum ‘Avenaceum’ when inoculation with the pathogen was made 24 hr after wounding. A nonpathogenic isolate of F. roseum ‘Gibbosum’ was used as the biocontrol agent in subsequent experiments to obtain more information on the protection phenomenon and to investigate the mechanism of biological control. Nine cultivars were protected by the biocontrol agent. Wounded carnation tissue without the agent gradually became resistant during 96 hr of incubation; however, application of F. roseum ‘Gibbosum’ to the infection court hastened this reaction so that comparable resistance was achieved in 24 hr of incubation. Among the potential mechanisms of biological control in this system, those involving antagonism (antibiosis, competition, and exploitation) and hastening of morphologically identifiable host responses were eliminated systematically. Conidia of the pathogen did not germinate in the infection court when the biocontrol agent was present, but germination of the pathogen was profuse when the agent was absent. Washed agar disks were incubated for 24 hr in infection courts infested with the biocontrol agent. When these disks were removed, they contained a substance(s) inhibitory to germination of pathogen conidia. Metal salts (HgCl2 and CuCl2) and an autoclaved mycelial preparation of the biocontrol agent also protected carnation tissue. These treatments have been effective in inducing the phytoalexin response in other plants.