Strategies for integrated deployment of host resistance and fungicides to sustain effective crop protection.

Sustainable crop protection is of key importance to food security and to ensure that crops make efficient use of resources (land, nitrogen and water). Fungicides and resistant cultivars are the predominant control measures against most crop diseases. However, control imposes a selection pressure on pathogen populations, leading to the evolution of pathogen strains which are less sensitive to the fungicides used or which are able to overcome host resistance (virulent pathogen strains). For example, potato late blight, caused by Phytophthora infestans, is managed by fungicide spray programmes, complemented by partial host resistance in some potato cultivars. Recently the pathogen population has changed: a loss of field efficacy of fluazinam (a widely used fungicide) has been reported, and new virulences have evolved, resulting in downgrading of cultivar resistance ratings.

Integrated control, where two or more control measures are applied, is widely believed to be more sustainable than over-reliance on one control option. There is however surprisingly little mechanistic understanding of the effects on pathogen evolution of combining deployment of fungicides and crop resistance genes. The evolution of fungicide insensitivity and the evolution of virulence are studied in isolation, despite a strong rationale for their being interactions between the two processes. New virulent or resistant strains gain a competitive advantage over existing 'wild-type' strains because they are able to grow more rapidly than wild-type strains in the presence of the control measure that they are able to overcome. However, epidemics of a new virulent strain will still be slowed by fungicides, thus reducing its competitive advantage. Hence, fungicides may slow selection for virulence and, by a similar process, cultivar resistance may slow selection for fungicide insensitivity.

The following hypotheses will be tested:
H1: Deployment of crop resistance reduces selection for fungicide insensitivity.
H2: Deployment of fungicides reduces selection for virulence.
H3: How crop resistance genes and fungicides are integrated is a key determinant of the durability of control.

Outcomes: The project will use experimental and modelling approaches to quantify the durability of disease control strategies integrating fungicide treatments and cultivar resistance. The directly applied outcome of the project is a fungicide and cultivar resistance based strategy for potato blight to be implemented through the Potato Council and industry partners. The further outcomes are generic methods to develop, parameterise and validate models that can be used to quantify integrated sustainable disease control strategies for pathogen-crop systems.

This work is made possible by recent progress in two areas. Firstly, changes in virulence in a range of pathogen species have been shown to be related to well characterised mutations in 'effector genes'. Testing for these mutations allows the proportion of virulent strains to be quantified in field experiments. Treatments can then be compared to measure the extent to which they affect selection for new strains. Fungicide insensitive strains can be tracked by similar methods. Secondly, epidemiological models have been tested against experimental data and found to give good predictions of the effect of fungicide treatments on selection for insensitive strains. Similar models have been developed to represent virulence evolution and it is now feasible to couple these two types of model to study the effects of integrated control.

Field experiments will generate epidemiological data and pathogen samples. The samples will be tested to quantify changes in the frequency of virulent and insensitive strains, under different treatments, to test hypotheses 1 and 2. The resulting data will be used to test a coupled mathematical model, which will then be used to explore integrated disease management strategies under hypothesis 3.

An epidemiological model will be developed that integrates the action of fungicides and cultivar resistance against a plant disease, when the pathogen is concurrently evolving insensitivity to the fungicide and virulence to overcome cultivar resistance.

We have previously gathered experimental data sets to validate/test our models for fungicide resistance evolution. Such testing had not been reported previously. The proposed project will allow us to gather data to validate our cultivar resistance/virulence model. This will be the first test of such a model in the scientific literature. The collection of a sufficiently large and detailed data set is enabled by expertise at the James Hutton Institute on the molecular biology of effector genes. This enables the quantification of selection for virulence in pathogen samples from field experiments, using PCR type techniques to track inoculated virulent and avirulent strains.

A set of experiments, on the pathogen Phytophthora infestans (causal organism of potato late blight) will test the hypothesis that cultivar resistance reduces selection for fungicide resistance. A second set of experiments will test the hypothesis that fungicide treatment slows evolution of virulence against cultivar resistance. The tested model will then be used to explore the dynamics of the effect of fungicides on the evolution of virulence, and the effect of the use of cultivar resistance on the evolution of fungicide insensitivity. Epidemiological phenotypes for host resistance and fungicide action, which are effective at constraining evolution, will be identified. Finally we will explore the combined deployment of the two crop protection methods to develop disease control strategies that are durable. These strategies for the durable control of potato blight should help to inform industry, via knowledge transfer pathways described in the impact plan.

The research will develop strategies for the durable control of potato blight through integrated use of fungicides and cultivar resistance. New insights arising from the project will generate messages for industry and revised guidance. Messages are likely to include, for example: (i) the extent to which the current balance between genetic and chemical control is appropriate to maximise durability of control, (ii) the epidemiological phenotypes of host resistance (e.g. whether the resistance predominantly reduces foliar infection, sporulation or tuber infection) which are most effective at slowing selection for insensitivity, (iii) the effects of deploying cultivars each with different resistance genes, compared against pyramiding genes, and (iv) the evolutionary effect of altering fungicide dose, according to the host resistance of cultivars. These messages will be exploited through existing mechanisms of communication by the Potato Council, the industry partners, and the Fungicide Resistance Action Group (FRAG). Messages will be presented to the wider stakeholder group through roadshows and demonstrations/posters at grower events, and at a European scale through the EuroBlight network (www.euroblight.net). These approaches to ensure impact have been used successfully by the project group in previous and on-going work.

Identification of outputs: The work in Objective 4 will lead to the outputs relevant to potato growers, agronomists, the crop protection industry and plant breeders. Starting in year 2 we will organise meetings of the investigators and project partners aimed at forming practical messages. At least three such meetings will be organised during the project. During these meetings we will also initiate the various activities for the 'application and exploitation' of outputs as described below.

Application and exploitation of the outputs: Established routes to impact which have proved to be effective will be exploited in the project.

- The proposers will present their work at roadshows and grower events such as Potatoes in Practice, the East of England Potato Day, the Potato Council Winter Fora, the ADAS/Syngenta Potato Conference, the Bayer CropScience Potato Meeting and the SAC Blight Event. These events, together with wider horticultural events, will be used to present findings to all relevant sectors of industry.
- Key messages can be conveyed to growers and the industry in the Scottish Agricultural College's (SAC) Crop Protection Report.

- The Potato Council (PC) will help interpret research findings into messages and guidance which is appropriate for crop consultants and individual growers. PC will also disseminate project findings through their KT initiatives; for example by Growers Advice Sheets.

- FRAG representatives will be invited to the meetings aimed at developing advice on durable control of potato blight. The PC/FRAG publication "Potato late blight: Guidelines for managing fungicide resistance" should be updated.

- EuroBlight : The proposers contribute to the EuroBlight Network to disseminate findings from their research on potato blight. EuroBlight organises a pan-European 3-day workshop every 18 months. Results will be presented and discussed at the workshops in October 2014 and May 2016. Workshop presentations are written up for the proceedings and made freely available via the EuroBlight website.

- The industry partners will use their existing routes to disseminate information from the project to their stakeholders. The project team will offer to disseminate findings at demonstration sites of the industry partners. The project will offer new approaches to disease management that aim to extend the life of fungicide active ingredients and the durability of cultivar resistance.

The combination of these routes to application and exploitation guarantees an efficient route to direct impact of project findings into farming, crop protection and plant breeding industries.