Leadbeater A. (2015): Recent developments and challenges in chemical disease control. Plant Protect. Sci., 51: 163-169.The use of chemical fungicides to control plant diseases is an integral component of crop management. Although fungicides have been used to good effect in agriculture since the 1940s, the introduction of new fungicides is an essential element to provide sustained control of major crop diseases. The need for new and innovative fungicides is driven, among other factors, by resistance management, regulatory hurdles, and increasing customer expectations. New fungicides can be discovered either within established mode of action groups, ideally with low resistance risk (robust modes of action), or in areas with completely novel modes of action. Compounds having a novel mode of action are of course of special interest, since they play a key role in resistance management strategies, but equally important are new fungicides with enhanced characteristics such as systemicity, curativity, and longevity of disease control. With the background of increasing registration hurdles, increasing costs, and increasing market needs, the current market position of major crop protection fungicides needs to be reviewed, along with the consideration of current and future market needs. An analysis of the situation regarding new fungicidal compounds in late development or recently introduced to the market suggests that considerable innovation continues to be delivered in the chemical fungicide area. New modes of action are quite rare in some segments (major new fungicides are mainly SDHIs), but seem to be more frequently discovered for the control of oomycetes. Potential reasons for this are discussed.
This chapter deals with the biochemical mode of action of quinone outside inhibitor (QoI) fungicides, which are respiration inhibitors; their fungicidal activity comes from their ability to inhibit mitochondrial respiration by binding at the so-called Qo site (the outer quinol-oxidation site or ubiquinol site) of the cytochrome bc1 enzyme complex (complex III), located in the inner mitochondrial membrane of fungi and other eukaryotes. It discusses the resistance risk to the QoIs; history of resistance to these fungicides; mutations associated with QoI resistance; and the monitoring for resistance to QoI fungicides. It is hoped that the experience of the QoI fungicides will help learning for the future novel classes of fungicides that will be introduced.
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