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Plant pathogen populations in wild and agricultural hosts and interactions with plant genotype - IF0188

Description
The fungus Sclerotinia sclerotiorum causes Sclerotinia disease on more than 400 plant species including both important crops and wild plants. In the UK, the incidence of Sclerotinia disease is increasing in crops (in 2008 the highest ever levels of Sclerotinia were recorded in oilseed rape (Brassica napus)). The trend for increasing Sclerotinia disease in oilseed rape is likely to continue because of the large area grown combined with shorter crop rotations and inoculum build-up in the soil as other crops such as lettuce and carrot become infected more frequently. Control of the disease relies on fungicides which target the airborne spores of S. sclerotiorum but timing of applications is difficult.

Moreover, reliance on fungicides is under threat because of the proposed changes to EU Directive 91/414 and there are also negative environmental and social impacts from the continued use of fungicides. Therefore, durable resistance to Sclerotinia is very desirable but at present there is no strong resistance to S. sclerotiorum in any cultivar of oilseed rape or of any of the other major crops affected. The first part of this project will screen brassica diversity sets, either already developed or currently being developed at WHRI as part of the Defra-funded Oilseed Rape Genetic Improvement Network (OREGIN) and the proposed Leafy Vegetable Genetic Improvement Network (VeGIN), for resistance to S. sclerotiorum. A key part of this work will be to identify appropriate S. sclerotiorum isolates for the screening as they vary in their aggressiveness.

Genetically characterised isolates from both wild and crop hosts will be studied so that representatives from commonly found genotypes with good potential to infect plants can be selected for the screening of brassica types. This approach will also establish whether S. sclerotiorum isolates representing genotypes from different wild and crop hosts are equally aggressive in causing disease on brassica plants and hence whether those isolates harboured by wild plants are a potential threat to nearby susceptible crops.

It is intended that information relating to the aggressiveness of S. sclerotiorum genotypes and any evidence for Sclerotinia resistance provided by this project would be used in the future as the foundation for industry funding through LINK / HGCA / HDC to:
i) introgress appropriate traits into commercial brassica cultivars and ii) establish effective screening protocols. This part of the project is relevant to Defra’s sustainable farming policy of ‘reducing the negative environmental footprint of agriculture as well as sustaining and enhancing the environment and biodiversity associated with farmland’ as the potential benefits of identifying host resistance to S. sclerotiorum include
ii) reducing waste associated with plant material rejected because of disease,
iii) maximising the efficiency of nitrogen inputs by reducing the number of infected plants, hence decreasing the risk of residues leaching into soil and water and
iv) reducing pesticide inputs and the potential impact on non-target organisms and the environment as well as the energy inputs and carbon costs associated with application.

The second part of this project will link with the first by investigating the extent to which S. sclerotiorum pathogen genotypes are shared between wild and crop hosts. In general the role of wild hosts in influencing the epidemiology and impact of plant diseases has largely been ignored despite the fact that they often harbour the same pathogens and are frequently intimately associated with agricultural ecosystems. Wild hosts can provide a means of survival between crops and be important sources of inoculum or pathogen vectors for crop plants. In addition, wild hosts may harbour sources of pathogen variation which can affect the dynamics of plant disease epidemics. For instance, genotypes from wild plants may respond differently to environmental factors or have increased aggressiveness on different crop species, varieties or other hosts. At the same time, pathogens from cultivated hosts may also have an impact on wild plant communities.

This means there is potential in many pathosystems for two-way gene flow and interaction across the agricultural / natural ecosystem interface. Such effects can have significant consequences for the occurrence of epidemics in both ecosystems as well as for pathogen evolution, wild plant diversity and disease management including the deployment of new crop varieties. As well as using S. sclerotiorum for wild and crop plant studies, a complementary pathosystem involving two virus complexes which infect wild and cultivated umbellifers will also be investigated. In both cases, genotype frequency and diversity in wild and crop hosts will be determined. Additionally in the virus pathosystem, the interactions of the viral complexes with the aphid vector involved will also be investigated. This information may then inform future disease management strategies for cropped areas where there are significant plant pathogen populations in natural plant communities nearby. This part of the project therefore fits within the Defra research theme of ‘Sustainable Farming Systems and Biodiversity’ as it aims to understand plant pathogen diversity and gene-flow in agroecosystems as a whole.

The specific objectives of the project are to: 1) determine the relative aggressiveness of S. sclerotiorum isolates from wild and crop hosts, 2) exploit S. sclerotiorum genotypes with defined aggressiveness to screen brassica diversity sets for resistance, 3) collect S. sclerotiorum and virus isolates from crop plants and wild hosts, 4) genotype the S. sclerotiorum and virus isolates using appropriate molecular techniques and 5) determine the frequency with which an aphid vector entering carrot crops is carrying viral-complex components.
Objective
7. (b) Objectives

The first part of this project will screen brassica diversity sets for resistance to the fungus Sclerotinia sclerotiorum, a major pathogen of oilseed rape (Brassica napus) and other crops worldwide. To ensure that appropriate pathogen isolates are used for the screening, genetically characterised isolates from both wild and crop hosts will initially be assessed for their aggressiveness so that representatives from commonly found genotypes with good potential to infect plants can be selected. This approach will also determine whether S. sclerotiorum isolates from wild plants pose a threat to susceptible crops. This links to the second part of the project where studies will establish to what extent S. sclerotiorum genotypes are shared between different wild and crop hosts by examining genotype frequency and diversity in both natural and agricultural ecosystems. Similar studies on wild and crop plants will also be done for a second contrasting pathosystem, a pair of virus complexes which affect umbellifers. In this latter pathosystem, the interactions of the viral complexes with the aphid vector involved will also be investigated.

The specific objectives of the project are to:

1) Determine the relative aggressiveness of S. sclerotiorum isolates from wild and crop hosts.
2) Exploit S. sclerotiorum genotypes with defined aggressiveness to screen brassica diversity sets for resistance.
3) Collect S. sclerotiorum and virus isolates from crop plants and wild hosts.
4) Genotype S. sclerotiorum and virus isolates using appropriate molecular techniques.
5) Determine the frequency with which an aphid vector entering carrot crops is carrying viral-complex components.
Project Documents
• EVID4 - Final project report : IF0188 Finalreport   (772k)
• ROAME Document : IF01   (165k)
Time-Scale and Cost
From: 2009

To: 2013

Cost: £594,000
Contractor / Funded Organisations
Warwick - HRI
Keywords
Brassicas              
Control              
Integrated Farming Systems              
Monitoring              
Pathogens              
Sustainable Farming and Food Science              
Sustainable Farming Systems