azoxystrobin and deoxynivalenol

Deoxynivalenol (DON) is a potent mycotoxin and virulence factor produced by Fusarium graminearum. We examined the expression of the core DON biosynthetic gene Tri5 during wheat head infection of susceptible and resistant cultivars and susceptible cultivars treated with strobilurin fungicides (e.g., azoxystrobin). DON was quantified to correlate expression with toxin accumulation. The highest Tri5 expression relative to housekeeping genes occurred at the infection front. As infection progressed, earliest-infected kernels showed diminished relative Tri5 expression but Tri5 expression never ceased during the 21 days observed. Azoxystrobin treatment showed no significant effect on either relative Tri5 expression or DON quantity. The resistant cultivar 'Alsen' showed minimal spread of the fungus, with no fungus detected by day 21. DON was not detected in significant quantities in Alsen in the later stages sampled. In Wheaten, DON levels were negligible at 8 days postinoculation (dpi), with detectable DON at later-sampled time points. Tri5 was detected even in fully senesced kernels 21 dpi. Our data demonstrate the presence of Tri5 transcripts in a susceptible cultivar over a much longer time period than has been previously documented. This suggests the ability of the fungus to rapidly resume toxin biosynthesis in dried infected grain should conducive environmental conditions be present, and provides a possible mechanism for high DON levels in asymptomatic grain.

Topics: Antifungal Agents; DNA, Fungal; Edible Grain; Food Contamination; Fungal Proteins; Fusarium; Gene Expression Regulation, Fungal; Methacrylates; Mycotoxins; Oligonucleotide Array Sequence Analysis; Plant Diseases; Plant Immunity; Pyrimidines; RNA, Fungal; RNA, Messenger; Strobilurins; Time Factors; Trichothecenes; Triticum; Virulence Factors

Fusarium head blight is a very important disease of small grain cereals with F. graminearum as one of the most important causal agents. It not only causes reduction in yield and quality but from a human and animal healthcare point of view, it produces mycotoxins such as deoxynivalenol (DON) which can accumulate to toxic levels. Little is known about external triggers influencing DON production.. In the present work, a combined in vivo/in vitro approach was used to test the effect of sub lethal fungicide treatments on DON production. Using a dilution series of prothioconazole, azoxystrobin and prothioconazole + fluoxastrobin, we demonstrated that sub lethal doses of prothioconazole coincide with an increase in DON production 48 h after fungicide treatment. In an artificial infection trial using wheat plants, the in vitro results of increased DON levels upon sub lethal prothioconazole application were confirmed illustrating the significance of these results from a practical point of view. In addition, further in vitro experiments revealed a timely hyperinduction of H2O2 production as fast as 4 h after amending cultures with prothioconazole. When applying H2O2 directly to germinating conidia, a similar induction of DON-production by F. graminearum was observed. The effect of sub lethal prothioconazole concentrations on DON production completely disappeared when applying catalase together with the fungicide.. These cumulative results suggest that H2O2 induced by sub lethal doses of the triazole fungicide prothioconazole acts as a trigger of DON biosynthesis. In a broader framework, this work clearly shows that DON production by the plant pathogen F. graminearum is the result of the interaction of fungal genomics and external environmental triggers.

Topics: Biomass; Catalase; Fungicides, Industrial; Fusarium; Hydrogen Peroxide; Methacrylates; Oxidative Stress; Oximes; Pyrimidines; Spores, Fungal; Statistics, Nonparametric; Strobilurins; Triazoles; Trichothecenes; Triticum