How to Detect and Measure Fungicide Resistance

Abstract

In recent years the effectiveness of control by fungicides is threatened by the phenomenon of fungicide resistance. The latter is defined as the stable, inheritable adjustment of a fungal cell or a fungal population to a fungicide, resulting in a less than normal sensitivity to that fungicide. The term fungicide resistance is used for strains of a sensitive species which have become, usually by mutation, significantly less sensitive to a fungicide. Application of the fungicide will select for the resistant strains, and thus favour their multiplication. When the major part of the pathogen population has become resistant, failure of disease control may occur (Delp and Dekker 1985). Problems caused by fungicide resistance have increased over the last 2 decades, since selective fungicides were introduced, many of which act systemically in the plant. These fungicides act at specific sites in the fungal metabolism. In contrast to these specific-site inhibitors, there have hardly been any resistance problems with conventional fungicides, such as copper compounds and dithiocarbamates. The latter interfere with many enzyme systems in the fungal metabolism and are calles multisite inhibitors. The relation between specific-site inhibitors and mutation towards resistance is briefly discussed in Section 3.1. For more detailed information about the genetic and biochemical basis of resistance, see Georgopoulos (1977) and Dekker (1985).