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 incWTing the cost disadvantages of multiple fermentation and processing protocols. Fusariwn Head Blight (FHB) antagonists Cryp/ococcusflovescens OR 182.9 (NRRL Y-302l6), C. oureusOR 71.4 (NRRL Y-302l3) and C. aureus OR 181.1 (NRRL Y -30215), were gro\Vll in twoand three-strain co-cultures to assess the quality and efficacy of the fermentation end products produced. Final cell COlllltS 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, DUllllett'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.