Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/8/2005
Publication Date: 7/7/2005
Citation: Zhang, S., Schisler, D.A., Boehm, M.J., Slininger, P.J. 2005. Carbon-to-nitrogen ratio and carbon loading of production media influence freeze-drying survival and biocontrol efficacy of Cryptococcus nodaensis OH 182.9. Phytopathology 95:626-632. Interpretive Summary: Fusarium head blight (FHB), caused by the fungus Gibberella zeae, is a devastating disease of wheat worldwide. A yeast we discovered named Cryptococcus nodaensis OH 182.9 effectively reduces this disease in greenhouse and field tests. Changing the amount and type of nutrients used to grow OH 182.9 could increase how well this yeast controls FHB and how easily this yeast can be dried for producing an effective biocontrol product. We conducted experiments to test the effect of changing nutritional factors, such as carbon-to-nitrogen (C/N) ratio and the carbon concentration of liquid production media, on viability of OH 182.9 after freeze-drying, and on biocontrol efficacy of fresh biomass in greenhouse tests. Survival of freeze-dried cells was greatest for cells grown for 48 h in C/N 30:1 medium. Cells harvested at 48 h generally survived freeze-drying better and were better at reducing FHB than those harvested at 72 h. The biomass produced at 48 h at the intermediate C/N ratios (9:1, 11:1, and 15:1) reduced symptoms of FHB as much as 83%. None of the treatments with cells harvested at 72 h consistently reduced FHB severity. With the results of this research, we can now improve the quality of OH 182.9 and have taken an important step towards achieving a commercial product for USDA-ARS customers to use in reducing FHB.
Technical Abstract: Fusarium head blight, caused by Gibberella zeae, is a devastating disease of wheat worldwide. Cryptococcus nodaensis OH 182.9 is an effective biocontrol agent for this disease. Development of a dried product of OH 182.9 would have potential advantages of ease of handling, favorable economics and acceptance by end users. OH 182.9 was grown for 48 and 72 h in semi-defined complete liquid medium (SDCL) with carbon-to-nitrogen (C/N) ratios of 6.5:1, 9:1, 11:1, 15:1, 30:1, and in SDCL C/N 30:1 media with varied carbon loadings of 7, 14, 21, and 28 g/L. Total biomass production and cell survival for 15 days after freeze-drying were evaluated. Biomass production of OH 182.9 was similar for all cultivation time by medium C/N or carbon loading combinations. In general, cells harvested at 48 h survived freeze-drying better than those harvested at 72 h. Survival of freeze-dried cells was greatest for cells grown for 48 h in C/N 30:1 medium. Cells produced in C/N 6.5:1 medium generally exhibited the poorest survival. For the C/N 30:1 media, cells from 7 g/L carbon loading medium harvested after 48 h had best survival after freeze-drying. The difference in freeze-dried cell populations between superior and inferior treatments was more than 3 log units 15 days after freeze-drying. The biomass of OH 182.9 produced in SDCL with varied C/N ratios and in SDCL C/N 30:1 media with differing carbon loadings was tested for biocontrol efficacy against FHB in greenhouse studies. The biomass harvested from SDCL C/N 9:1, 11:1, and 15:1 media after 48 h significantly reduced symptoms of FHB. None of the treatments with cells harvested at 72 h consistently reduced FHB severity (P less than or equal to 0.05). Cells grown in SDCL C/N 30:1 media with 7 and 14 g/L carbon loading reduced FHB disease severity. Cells harvested from SDCL C/N 9:1, 11:1, and 30:1 with 14 g/L carbon increased the 100-kernel weight compared to the disease control. Data from this research demonstrate the potential of improving OH 182.9 product quality via management of the nutritional environment of the production medium.