Effect of carbon, nitrogen, and C:N ratio on growth, sporulation, and biocontrol efficacy of Talaromyces flavus

Five-day biomass production by the biocontrol fungus Talaromyces flavus was measured in a liquid basal medium, pH 5.5, containing each of 37 carbon (C) sources with a single nitrogen (N) source, and each of 42 N sources with a single C source. In general, production of biomass was greatest on complex sugars such as polysaccharides (32 g/liter of medium) and beta-glucosides (2.4 g/liter of medium), and was least on monosaccharides (1.3 g/liter of medium). Ascospore production at 6 weeks on solid basal medium with the same amount of these same 37 degrees C sources was greatest on oligosaccharides (2.9 x 10(8) spores per 5.5-cm-diameter petri dish), and least on polysaccharides and monosaccharides (1.6 and 1.4 x 10(8) spores per 5.5-cm-diameter petri dish, respectively). For C sources, there was no correlation between production of ascospores and hyphal dry weight. The various N sources yielded 0 to 10(9) ascospores per 5.5-cm-diameter petri dish and 10(-4) to 10(-5) g of hyphal dry weight per milliliter. In general, N sources that resulted in the greatest number of ascospores also yielded the greatest hyphal dry weights. For the two C and two N sources tested, the number of ascospores increased as the ratio of C to N increased from 5:1 to 30:1. This effect was most obvious as the C:N ratio increased from 5:1 to 15:1. At low C:N ratios (<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 ratios 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 that slightly increased ascospore production of T. flavus reduced efficacy of biocontrol of Verticillium wilt compared with ascospores produced on PDA.