Co-culture of Yeast Antagonists of Fusarium Head Blight and their Effect on Disease Development in Wheat

Multistrain mixtures of biocontrol agents which can reduce plant disease to a greater extent than the individual strains of the mixture, commonly, are prepared by blending separately produced fermentation products. Co-cultivation of strains to equivalent biomass yields would provide mixture advantages without incurring the cost disadvantages of multiple fermentation and processing protocols. Fusariwn Head Blight (FHB) antagonists Cryptococcus flavescens OR 182.9 (NRRL Y-302l6), C. aureus OH 181.1 (NRRL Y-302l5) and C. aureus OR 181.1 (NRRL Y -30215), were grown in two- and three-strain co-cultures to assess the quality and efficacy of the fermentation end products produced. Final cell counts of component strains of all co-cultures produced were equivalent when plated on a medilllll that contained the trisaccharide melezitose as a sole carbon source and produced colonies of strain-distinguishable sizes. Co-cultures of C. flavescens OH 182.9 and C. aureus OH 71.4 significantly reduced FHB disease severity (32%, p = 0.05, Dunnett's t-test) when averaged across four greenhouse studies. In wheat field trials, biomass from co-cultures of these two strains reduced FHB incidence in some cases but rarely other FHB disease parameters (p = 0.05, Bonferoni mean separation). Relative Performance Index (RPI) analysis of the overall effect of treatments at both field sites revealed that treatment with the OH 71.4 and OH 182.9 co-culture significantly reduced FHB, as evidence by a higher RPI value than for the control, while the individual strains did not. The potential for obtaining superior efficacy and cost benefits with multi-strain cultures of biocontrol agents justifies additional research effort.