Prediction of fungicidal resistance

Management of fungicide resistance requires some means of predicting the quantitative response of the target fungus population to various management alternatives. 

The dominant role of selection in the evolution of fungicide resistance within a fungal pathogen population is readily apparent (2). Thus, any use of the at risk" fungicide will influence evolution of the population. And, appropriately, consideration of selection has dominated our thinking. Predictions concerning the influence of selection on plant pathogen populations have been made with the aid of mathematical models Q, 4, 5, 6, 2). 

The alternation of fungicides with different biochemical action seems to be the most practical strategy for suppressing the buildup of fungicide-resistant Penicillium on citrus fruits. Selection pressure for multiplication of a resistant biotype can be completely eliminated from the treatment cycle until the resistant biotype is suppressed by more fit wild biotypes in the population. For complete coverage applications, such as postharvest treatments, the model of Kable and Jeffrey (44) predicts that resistance will build up more slowly when two fungicides are alternated rather than mixed. 

BRENT ETAL. Predicting Evolution of Fungicide Resistance... 

Table IV. Predicted relative effects of various management strategies on fungicide resistance and disease suppression using PhyCophthora infesCans Solanum tuberosum and protectant and systemic fungicides via simulation analysis Data are from Milgroom and Fry (1)...

A knowledge of the potential for genetic variation in fungicide sensitivity in pathogen populations is central to prediction of resistance. Potential variation may be revealed by several methods in the laboratory and field, including mutagenesis, recombination and selection experiments, and monitoring. Benefits and drawbacks of these methods are considered. 

When we introduce new fungicides, it is necessaiy to evaluate how quickly resistant strains can appear and increase with the use of fungicides. It is generally useful to elucidate the mode of action of newly developed products when predicting the inherent risk for resistance development, as most fungicides that have encountered resistance so far were site-specific inhibitors such as benzimidazoles, Qols and MBI-Ds. 

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