Characterization and field detection of Cryptococcus flavescens strains, biocontrol agents against Fusarium head blight of wheat
X. RONG (1), P. A. Paul (1), D. A. Schisler (2), B. B. McSpadden Gardener (1). (1) Ohio State University, OARDC, Wooster, OH, U.S.A.; (2) Crop Bioprotection Research, USDA-ARS, Peoria, IL, U.S.A.
<i>Cryptococcus flavescens</i> strain OH182.9_3C (3C) previously exhibited remarkable biological control efficacy against Fusarium Head Blight (FHB), a globally important disease of wheat. Multilocus sequence typing was performed on 3C and 11 other <i>Cryptococcus flavescens</i> strains using loci within the genes of β-tubulin, Chitin Synthase 1, Elongation Factor 1, Heat Shock Protein 70 kDa and Internal transcribed Spacer regions. Two genotypes, 3C type (5 strains) and non-3C type (7 strains), were revealed by all the four protein-encoding genes with high bootstrap support. Phenotypic assays using Biolog showed all the strains of non-3C type as one distinct group and slow assimilation of several carbon sources by two strains of 3C type. 3C-type strains showed higher biocontrol efficacy than non-3C type in a green-house bioassay against FHB. To assess the environmental risk of 3C as a biopesticide, a quantitative PCR (qPCR) assay of SYBR® Green chemistry targeting a Heat Shock Protein 70 kDa gene was developed and applied to monitor the population dynamics of 3C-like <i>C. flavescens</i> in wheat fields and on harvested grains. qPCR results demonstrated that 3C was able to colonize inoculated wheat heads in field at the magnitude of 10<sup>4.5</sup> to 10<sup>6.5</sup> target gene copies per gram wheat, which was comparable to the inoculation rates. 3C population dispersed from inoculated areas to non-inoculated areas in a stochastic fashion during the growing season.
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