(2010) showed that in vitro adaptation of F. graminearum NIV chemotype to sublethal dose of tebuconazole resulted in recovering isolates producing higher levels of NIV. In the present study, RT-qPCR results did not always parallel the trichothecene accumulation. Three different explanations of this discrepancy are possible. Firstly, the commonly observed low toxin production of F. graminearum in axenic cultures
(Gardiner et al., 2009) results in a lack of considerable differences between the treated samples and N.T.C. This was especially evident in the samples of 15ADON chemotype treated with propiconazole. Notably, in these samples, an increase in the amount of tri transcripts was lower than in tebuconazole-treated samples Sirolimus purchase where a higher level of toxins was quantitated. It is tempting to speculate that relatively low tri transcript level in propiconazole-treated samples was the result of selleck chemical less effective induction of H2O2 in the fungus. Ponts et al. (2007) demonstrated that treatment of 15ADON chemotype of F. graminearum with H2O2 resulted in up to 11- and 19-fold increase in tri4 and tri5 transcript levels, respectively. Our results showed that most of the propiconazole-treated samples resulted in a lower tri transcript levels as observed by Ponts et al. (2007), which probably affected low toxin accumulation. Secondly, trichothecene accumulation by azole stress could result from an unknown, additional Sunitinib modulation mechanism
which is independent from transcriptional regulation. This hypothesis was suggested by Ponts et al. (2009) who demonstrated differential antioxidant defense responses within F. graminearum strains to H2O2. Thirdly, the discrepancies
could also result from variation between the fungal cultures studied. Both RT-qPCR and toxicological analysis were performed on different fungal cultures that might differ at transcriptional levels. We found that despite theoretically identical conditions, the results from two biological replications differed in some cases in the level of tri transcript (data not shown). Such variation could result from partial nutrient deficiency that is exhausted rapidly on agar media (Schmidt-Heydt et al., 2008). Notably, intraculture differences have been observed by Ochiai et al. (2007) who demonstrated differential tri5 transcript levels in fungal hyphae. Moreover, a recent study by Audenaert et al. (2012) demonstrated the increased sensitivity of a tri5 knockout mutant compared to its wild-type parent strain, which indicated that biosynthesis of trichothecenes might also have a physiological meaning. In an in planta experiment, we analyzed whether treatment of inoculated wheat heads with sublethal azole concentrations could increase fungal DNA and toxin levels in the grain. The presence of azoles in wheat heads was confirmed within 24 h of the first fungicide spraying. The concentrations of azoles differed and values ranged from nondetectable to 1.04 and 6.