Managing concurrent evolution of resistance to fungicides (PhD)

Evolution of resistance to fungicides threatens the control of plant pathogens.

Resistance management tactics, such as the application of fungicides with different modes of action (MoA) in mixture or alternation, can slow selection for resistance.

However, it is unclear which strategies work against resistance evolving concurrently to two or more MoA.

In this project, mathematical epidemiological models of polycyclic fungal foliar diseases were used to investigate potential resistance management tactics.

Use of integrated pest management (IPM) can reduce the fungicide intensity required for disease control, but resistance management benefits of cultural control methods are rarely quantified.

A model was developed to estimate the resistance management benefits of a phytosanitary cultural control measure – the ‘soybean-free period’ – used in Brazil to delay infection of soybean crops by Phakopsora pachyrhizi (Asian soybean rust).

The interactions associated with the use of fungicide mixtures and varying dose, application rates and timings were considered.

Mixing two MoAs may require splitting the total dose of each MoA across more applications, increasing exposure time.

Using a model of Zymoseptoria tritici (septoria tritici blotch), it was shown that dose splitting of a solo MoA increases selection, but the effect varies with fungicide properties and the type and magnitude of resistance.

Alternation with ‘splitting and mixing’ as tactics against concurrent evolution of resistance to two MoA was then compared, modelling a sexually reproducing Z. tritici population.

The best strategy varied with fungicide and resistant strain properties.

Incomplete cross-resistance between active substances with the same MoA could potentially be utilised for resistance management. 

A novel modelling approach was used to investigate the resistance management benefits of within-MoA mixtures with incomplete cross-resistance.

Resistance management benefits were greatest when the level of cross-resistance between active substances was low or negative; the rate of selection was also dependent on the variation in the fitness of pathogen strains against individual mixture components.

Student: Isabel Corkley (Rothamsted Research and University of Reading).

Supervisors: Dr Alice Milne (Rothamsted Research) and Dr Alexey Mikaberidze (University of Reading).