Tri5 gene expression analysis during postharvest storage of wheat grain from field plots treated with a triazole and a strobilurin fungicide

Authors: BOLANOS-CARRIEL, CARLOS - University Of Nebraska; WEGULO, STEPHEN - University Of Nebraska; BAENZIGER, STEPHEN - University Of Nebraska; ESKRIDGE, KENT - University Of Nebraska; Funnell-Harris, Deanna; MCMASTER, NIKKI - Virginia Tech; SCHMALE III, DAVID - Virginia Tech; HALLEN-ADAMS, HEATHER - University Of Nebraska

Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2019
Publication Date: 1/20/2020
Citation: Bolanos-Carriel, C., Wegulo, S.N., Baenziger, S.P., Eskridge, K.M., Funnell-Harris, D.L., Mcmaster, N., Schmale III, D.G., Hallen-Adams, H.E. 2020. Tri5 gene expression analysis during postharvest storage of wheat grain from field plots treated with a triazole and a strobilurin fungicide. Canadian Journal of Plant Pathology. 42(4):547-559. https://doi.org/10.1080/07060661.2019.1700169.
DOI: https://doi.org/10.1080/07060661.2019.1700169

Interpretive Summary: Fusarium head blight (FHB) and the resulting toxin deoxynivalenol (DON) have a huge impact on wheat producers and industries worldwide. In the United States, FHB is mainly caused by the fungus Fusarium graminearum. This research used a PCR technique to evaluate the expression level of a gene, called Tri5, that the fungus expresses during DON production. Expression of this gene was monitored in stored wheat grain grown under different management systems. The grain was grown on hard-red winter wheat cultivars that were either susceptible or moderately resistant to FHB. Field plots of each cultivar were either treated or untreated with fungicides with two different chemistries: a triazole and a strobilurin. Infected wheat collected from field plots were put in storage and periodically sampled, then toxin gene expression was determined. Grain from the susceptible cultivar had higher levels of Tri5 gene expression than grain from the moderately-resistant cultivar. However, the amount of DON in grain was not always associated with Tri5 expression; therefore, expression of Tri5 levels cannot be used to predict DON levels. Tri5 gene expression was similar in strobilurin-treated compared to untreated wheat grain. However, Tri5 expression was lower in grain from the susceptible cultivar treated with triazole fungicide, even after 120 days in storage, than in untreated grain from the susceptible cultivar. Overall, Tri5 expression levels increased during storage of high-moisture grain showing that these toxin-producing fungi may survive and continue producing toxin in wheat kernels for several months after harvest.

Technical Abstract: Fusarium head blight (FHB) and the associated mycotoxin deoxynivalenol (DON) negatively impact the wheat industry worldwide. In the United States, FHB is mainly caused by Fusarium graminearum sensu stricto. The purpose of this study was to evaluate, under storage conditions, the expression of the DON biosynthetic gene trichodiene synthase (Tri5) of F. graminearum in grain of hard-red winter wheat cultivars Overley (FHB-susceptible) and Overland (moderately resistant to FHB) from field plots treated or untreated with the triazole fungicide Prosaro and the strobilurin fungicide Headline. Infected grain was stored and periodically sampled to determine gene expression using qRT-PCR. The F. graminearum housekeeping gene GAPDH was consistently detected, indicative of metabolically active fungi, and Tri5 detection was significantly higher in cv. Overley compared to cv. Overland. Tri5 gene expression and DON concentrations showed little to no correlation; consequently, Tri5 expression levels did not accurately predict DON concentrations. Headline did not significantly reduce Tri5 gene expression compared with untreated wheat. In the Prosaro treatment, a significant reduction in the relative expression of Tri5 was detected after 120 days, as well as a downregulation of Tri5 from 60 to 120 days of storage in cv. Overley. In grain from Headline-treated plots of both cultivars, the expression of Tri5 increased from 0 to 30 days after tempering. Genetic expression of Tri5 that is necessary for the production of DON can increase during storage of high-moisture grain. Fusarium fungi can persist in wheat kernels for several months post-harvest and may actively produce toxin during this period.