Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/1997
Publication Date: N/A
Citation: Interpretive Summary: The naturally-occurring, beneficial fungus Talaromyces flavus controls the plant pathogenic fungus Verticillium dahliae that causes a wilt disease in more than 250 species of plants worldwide. For T. flavus to be produced in the quantities needed for agricultural production systems, the nutritional requirements of T. flavus must be known. This work was undertaken to determine what carbon and nitrogen sources give maximum production of the desired spore type of T. flavus. Further, we wished to determine if the spores produced with these carbon and nitrogen sources are as efficacious as those produced with standard potato dextrose agar. Each of 37 carbon and 42 nitrogen sources were substituted for the carbon and nitrogen sources in a defined growth medium, Biomass after 5 days in liquid culture and sporulation after 6 weeks on agar were determined. IN general, spore and biomass production were greatest on complex sugars and least on simple sugars, although carbon sources that resulted in the greatest biomass were not necessarily those that gave the most spores. In contrast, the nitrogen sources that resulted in the greatest biomass also produced the most spores. The ratio of carbon to nitrogen also affected biomass and spore production. Spores produced on potato dextrose agar were significantly better at protecting eggplants from Verticillium wilt than spores produced on high or low-yielding carbon or nitrogen sources. This work indicates that conditions favoring maximum production of spores or biomass reduce the efficiency of biocontrol. This information will be used by scientists developing mass production methods for biocontrol fungi.
Technical Abstract: Biomass production in 5 days and sporulation in 6 wk by the biocontrol fungus Talaromyces flavus were measured in a medium containing each of 37 carbon (C) and 42 nitrogen (N) sources. Production of biomass was greatest on complex sugars such as polysaccharides, beta-glucosides, and was least on monosaccharides. Ascospore production was greatest on oligosaccharides, ,and least on polysaccharides and monosaccharides. There was no correlatio between production of ascospores and hyphal dry weight, and this relationship varied greatly among C sources. Eleven and 28 of the N sources tested, resulted in ascospore numbers and biomass, respectively, greater than the treatment without a N source. In general, N sources that resulted in the greatest number of ascospores also yielded the greatest hyphal dry weights. The ratio of C to N also affected growth parameters. As the ratio of C to N increased from 5:1 to 30:1, the number of ascospores sincreased. At low C:N ratios (less than 15:1), treatments with hypoxanthine as a N source resulted in significantly greater production of biomass than treatments with ammonium tartrate; no difference was observed at C:N ratio greater than or equal to 15:1. Incidence of Verticillium wilt was 50% lower for eggplants drenched with ascospores grown on potato dextrose agar (PDA) compared with eggplants either nondrenched or drenched with ascospores grown on media with hypoxanthine plus lactose or maltose. Thus, C and N sources which increaesd biomass amd ascospores production of T. flavus reduced efficacy of biocontrol of Verticillium wilt compared to T. flavus produced on PDA.