What is fungicide resistance?
Fungicide resistance is “the stable, inheritable adjustment by a fungus to a fungicide, resulting in a less than normal sensitivity to that fungicide” (Dekker, 1995). In other words, fungicides don’t work as well, or at all, on populations of fungi that have become less sensitive to them. Since fungicide resistance develops on a genetic level, off-spring of such fungi are also resistant.
Fungicides usually act by inhibiting important processes in fungi such as cell division (benzimidazoles), sterol formation (DMI fungicides), or other general metabolic activities in fungi (dicarboximides, chlorothalonil, quintozene, dithiocarbamates). Within populations of fungi, there may be particular individuals that are mutants and can tolerate a larger dose of the fungicide than their normal relatives. In these mutants, some process is altered so that the fungicide either does not penetrate to the site of action within the organism, or the site of action is altered so that the fungicide cannot fully exert its effect. An individual that is resistant to a particular fungicide generally will show resistance to another fungicide that has the same mode of action. For example, benomyl (Tersan 1991) and thiophanate-methyl (Easout) have the same mode of action, and organisms resistant to one will show cross-resistance to the other one. Another major group of fungicides which shows cross-r
