Combating Fungicide Resistant Crop Pathogens: Discovery of Metyltetraprole

Abstract

The call for chemical load reduction on farmland has become stronger in recent years. Nevertheless, conventional farming systems achieving high yields can contribute to conservation by preventing additional natural habitats from being converted to farmland; indeed limiting the expansion of farmland seems to be more beneficial for the environment when compared to low yielding “eco-friendly agriculture”. Conserved non-farmland can also serve as carbon storage areas limiting carbon emissions. However, it has also been shown that intensive farming with high yield potential can be associated with an elevated risk of pests and diseases. To minimize the risk of both chemical overloading and yield loss, utilization of highly effective crop protection products with improved safety would be an important action for the agricultural industry. Such pragmatic insights have motivated many researchers developing improved agrochemicals. In fact, the chemical input on farmland has decreased dramatically since the invention of modern synthetic agrochemicals when compared to non-selective toxic chemicals such as arsenic and organomercury, which were used during the early days of pesticide use. Since synthetic agrochemicals were first used, their amount has been gradually decreasing thanks to their improved efficiency per chemical unit. For example, sulfur for controlling powdery mildew required thousands of grams per hectare while benzimidazoles, one of the first synthetic systemic fungicides, only requires hundreds of grams per hectare to be effective. Moreover, recent compounds launched in the 21st century are generally applied at around 100 grams per hectare, showing further reduction in quantities of agrochemicals used. However, the use of such modern synthetic agrochemicals in agriculture is under increasing threat. One is an increasing restriction of the usage of chemicals. Another is the development of resistance to agrochemicals in agricultural pathogens, pests, and weeds owing to selection pressure by crop protection products. For example, the number of reported weed species that have acquired resistance to glyphosate is increasing each year, driving the introduction of new generation genetically modified (GMO) crops with traits of auxin herbicide tolerance. All of the biggest three fungicide classes used by farmers globally (DMIs demethylation inhibitors)-, QoIs – quinone outside inhibitors, and SDHIs – succinate dehydrogenase inhibitors) are now threatened by resistant populations of key crop pathogens, including Zymoseptoria tritici, the causal agent of septoria tritici blotch of wheat in Europe. These three groups of chemicals make up more than 70% of global fungicide use, with few alternative choices showing equivalent efficacy and spectrum (based on product area treated). Furthermore, the introduction of newer chemical classes is very limited, owing to the difficulty in achieving a combination of effectiveness as a fungicide, mammalian and environmental safety, and economic feasibility in terms of costs of production and development. Metyltetraprole is a new tool to combat current problematic fungicide-resistant populations of key pathogens. The aim is to deliver this innovative modern technology to many users who have difficulty in managing crop diseases, in order to contribute to global sustainability by maintaining the efficiency of food production in the existing farmlands.