Downy Mildew and Late Blight Control (CP 184)

Integrated management strategies are fundamental to sustainable crop production. Diseases caused by aerial oomycetes typically exhibit rapid epidemics and have the potential to cause complete crop loss. Control options are limited, or under-utilised, and control currently relies heavily on the application of pesticides. An approach which combines several control options and optimises the use and impact of each is desirable. This project aims, through the provision of reviews and best practice grower guides, to consolidate current knowledge, ensuring that measures which could be taken up are quickly disseminated and potential barriers to uptake identified. The project builds on current knowledge of specific pathosystems (in particular downy mildew on onion, lettuce, spinach and basil) and develops and validates the tools required for a long term integrated approach to disease management.  

New tools for the genotypic analysis of Bremia lactucae populations, linked to phenotypic characteristics such as race and fungicide sensitivity, will allow an understanding of population diversity to directly inform resistance breeding and fungicide stewardship for the first time. This approach has previously been used very successfully for potato late blight. A funded project on onion downy mildew fulfils the remit for real-time disease risk monitoring and will be built upon with the incorporation of a B. lactucae diagnostic test. Knowledge gaps in the epidemiology of the diseases, including the importance of seed-borne inoculum in pathogen transmission, will be addressed and cultural control in a protected environment evaluated. All outcomes will be disseminated through a comprehensive KE programme. 

Project Headlines:

Integrated management is now essential for the effective management of downy mildews on horticultural crops.  This ambitious project brings together several lines of investigation including:

1) The development of new molecular tests to detect and quantify downy mildew pathogens in basil, spinach and column stock seed-lots;

2) Heat treatments were demonstrated to be effective at removing infections from contaminated seeds;

3) PMA-qPCR was ‘road-tested’ for testing seed for viable low-level downy mildew infections – whilst it works, it is very involved and only currently suitable as a very specialised laboratory method for detecting and quantifying low level infections;

4) Lettuce downy mildew race typing and fungicide resistance testing;

5) Updated information about the resistance of lettuce, spinach and column stock downy mildew populations to approved and widely used fungicides;

6) Reviews on the general biology and control of 14 horticulturally important downy mildews, the potential for using elicitors in integrated control and the current state of development of Decision Support Systems/Tools for the management of downy mildews maximise integrated management possibilities.

The project aims to improve integrated management of important horticultural diseases caused by aerial oomycetes. This will be achieved through the development of new tools, an improved knowledge of the epidemiology and control of key diseases and the consolidation of existing information. Knowledge exchange is central to the delivery of the aim.  

The core objectives of the project are:   

• Review and collate information on the pathogen biology and disease epidemiology of aerial oomycetes to inform the development of integrated management practices.  

• Review methods for the control of infectious propagules (oospores, zoospores, sporangia, conidia) in irrigation water, crop debris, soil and growing media, making a comparison of the advantages/disadvantages of various methods and inform growers on routes of infection.   

• Develop IPM programmes for aerial oomycetes using information from SCEPTREplus and with fungicide stewardship as a priority.   

• Develop a service using validated tests to monitor fungicide sensitivity in key aerial oomycetes.    

• Provide a comprehensive package of work on lettuce downy mildew Bremia lactucae to include development of markers with which to assess population diversity, association of race type, fungicide sensitivity and other phenotypic characteristics with genotype in anticipation of a service for provision of outbreak information to growers and to inform IPM and breeding activities.    

• Development/validation of in-field and/or laboratory diagnostics