Resistance development, fungicide

From the particularities above outlined, we know which chemicals can be utilized with minimal probabilities of resistance development. Among these compositions are the subject fungicides of this paper - the sulfenimides. 

Recent experience with fungicide resistance underlines the need for the early development and implementation of effective, realistic, and enforceable anti-resistance strategies. These strategies should be developed by the agrochemical industry in collaboration with extramural partners. This partnership should also address the manifold problems that remain to be solved to protect the powerful and highly needed modern fungicides from becoming obsolete due to broad resistance development. 

In the case of pyrimidines and benzimidazoles. the first groups of fungicides against which resistance occurred quickly after market introduction, to our knowledge the risk of resistance development was not evaluated, nor was the phenomenon expected to show up. In... 

The rarer that resistant mutants are in the initial population, the longer that resistance will take to develop. Poor fitness may prevent the development of resistance, but fungicide selection pressures are sometimes extremely strong, especially in enclosed environments such as packing-sheds and glass-houses, so that relative unfitness of resistant forms will only slow down the evolution of resistance substantially if the fungicide is not used continuously. 

VIII. Discover and Develop Fungicides with New Modes of Action. The discovery of new fungicide target sites is required to compensate for the loss of products due to de-registration and resistance. 

If it were possible to develop two pesticides such that increased resistance to one of them led to increased susceptibility to the other, resistance development would at least be delayed. There is one example of this principle. The systemic fungicide diethofencarb is particularly effective against Botrytis spp., which are resistant against benzimidazole. Benzimidazoles like car-bendazim and thiophanate bind to a site on the tubulin protein and inhibit mitosis. Resistant Botrytis has a tubulin that does not bind benzimidazoles, but may bind diethofencarb better. 

The nearly identical mode of action of benzimidazoles, evidenced by the similarity of their fungitoxic range of action and of their structure, is also supported by the development of cross-resistance. Resistance developed rather rapidly to systemic fungicides has also been observed for benzimidazole derivatives. 

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