Non-viable antagonist cells are associated with reduced biocontrol performance by viable cells of the yeast Papiliotrema flavescens against Fusarium head blight of wheat.

Authors: Schisler, David; Yoshioka, Miho; Vaughan, Martha; Dunlap, Christopher

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/2/2017
Publication Date: 12/4/2017
Citation: Schisler, D.A., Yoshioka, M., Vaughan, M.M., Dunlap, C.A. 2017. Non-viable antagonist cells are associated with reduced biocontrol performance by viable cells of the yeast Papiliotrema flavescens against Fusarium head blight of wheat.. Meeting Abstract.

Interpretive Summary:

Technical Abstract: Microbially-based plant disease control products have achieved commercial market success, but the efficacy of such biocontrol products is sometimes deemed inconsistent. Improper processing of harvested microbial biomass or long-term storage can reduce the proportion of viable cells and necessitate the use of more biomass to achieve the desired concentration of viable cells in the final formulated biocontrol product. We hypothesized that non-viable cells, when in sufficient quantity within a formulation, could provide a nutritive benefit to plant pathogen propagules and therefore reduce the efficacy of a biocontrol product. To test this hypothesis we used Fusarium graminearum, an important causal agent of Fusarium head blight (FHB) of wheat, and the yeast Papiliotrema flavescens (formerly Cryptococcus flavescens) strain OH 182.9 3C, a proven antagonist of the FHB pathogen. In glasshouse experiments, wheat florets were injected with fixed amounts of F. graminearum conidia (~1 x 10E+4 conidia/ml), viable cells of P. flavescens (~1 x 10E+9 cfu/ml) and varying concentrations of non-viable P. flavescens cells including 0 as a control, ~1 x 10E+9/ml, and ~2 x 10E+9/ml. In the absence of non-viable cells, P. flavescens consistently reduced FHB severity by more than 50%. However, when co-inoculated with low or high levels of dead cells, viable cells of P. flavescens did not suppress disease. Instead, disease increased by >150% (P<0.05, FPLSD) compared to the treatment with only viable biocontrol cells. Interestingly, the wheat heads treated with viable and non-viable P. flavescens cells displayed greater disease severity than heads inoculated with only the F. graminearum pathogen. When F. graminearum was grown in a liquid basal salts medium without carbon or nitrogen but supplemented with increasing levels of non-viable cells of antagonist strain OH 182.9 3C, the amount of pathogen biomass increased (P<0.05) for each sequentially higher level of non-viable cell amendment tested. Scanning electron microscopy indicated that the presence of non-viable P. flavescens cells modified the ectotrophic growth of F. graminearum on wheat lemma tissue in situ. Results indicate that non-viable antagonist cells present in a viable biocontrol cell treatment can reduce the extent of disease control or even reverse the outcome that the biological control treatment would otherwise achieve.