Pleiotropic effects are one of the main concerns regarding genetically modified organisms (GMOs). This includes unintended side effects of the transgene or its genome insertion site on the regulation of other endogenous genes, which could potentially cause the accumulation of different secondary metabolites that may have not only an impact on diet as repeatedly worried by the public but also on the environment. Regarding amt. and possible environmental effects, flavonoids represent the most prominent group of secondary metabolites in wheat. Many flavonoids function as signalling or defense mols. We used a robust and reproducible anal. method to compare the flavonoid content of genetically modified (GM) wheat (Triticum aestivum L., Gramineae) expressing genes that confer increased fungal resistance with their non-GM siblings. The transgenes provide either a broad-spectrum fungal defense (chitinase/glucanase from barley) or bunt-specific resistance by a viral gene (KP4). Significant differences in flavonoid compn. were found between different wheat varieties whereas different lines of GM wheat with increased antifungal resistance showed only minor differences in their flavonoid compn. relative to their non-GM siblings. In a field test, no significant differences were detectable between infected and non-infected wheat of the same variety regardless of the presence of the transgene. Our results are in agreement with the hypothesis that the transgenes we used to increase wheat defense to fungal pathogens do not interfere with the flavonoid biosynthesis pathway. More significantly, the genetic background resulting from conventional breeding has a direct impact on the biol. compn. of flavonoids, and thus possibly on the environment. [on SciFinder (R)]