Contemplations and speculations on novel approaches in the control of fungal plant diseases

Plant disease control can, in principle, be achieved by direct and indirect methods. Novel approaches in direct plant disease control are illustrated by the group of ergosterol biosynthesis inhibitors. Consideration of their stereochemistry leads to speculations on a more rational design of chiral fungicides, with possibly optimised activity against a wider range of fungi. Studies on the mode of action of ergosterol biosynthesis inhibitors, and of the mechanism of resistance to them in fungi, suggest that these phenomena are not causally related. At least in laboratory mutants, resistance seems to be associated with altered membrane function, which may account for reduced fitness, and, in pathogens, for reduced virulence as well. The results of these studies strengthen the conclusion that knowledge of the modes of action and mechanisms of resistance, at the physiological, biochemical and molecular level, should provide a rationale on which to base the design of new systemic fungicides. As a matter of more immediate practical importance, the implications of the use of fungicide‐synergist combinations in plant disease control are briefly discussed. With respect to indirect plant disease control, novel approaches should be directed towards the activation of host resistance. However, prospects seem to be limited for the successful application of alternative chemicals that act on host resistance mechanisms by, for instance, inducing phytoalexin synthesis. Controlled activation of host resistance by localised sensitisation of resistance mechanisms may, however, become a promising new method of plant disease control in the future.