CP 191 Bacterial Pathogens of UK Crops

Summary: There are more than one hundred known bacterial plant pathogens that affect or could potentially affect UK crops. Despite much previous research, diseases caused by bacterial pathogens continue to cause economic losses to growers, particularly in field vegetables, hardy nursery stock and protected ornamentals. The options for control with plant protection products have always been limited, and it is likely that this will continue.

For the majority of bacterial plant diseases the primary source of infection is likely to be the seed or propagation material. The use of clean starting material provides the best prospects long-term sustainable control of bacterial pathogens in horticultural crops, the exclusion of the pathogen through the use of clean starting material avoids the need for secondary interventions with e.g. plant protection products etc.

This is a collaborative project between PHS, STC, WCC and growers and will primarily focus on developing best practice for the deployment of such a strategy. For a number of high priority model bacterial pathogens the prevalence of the pathogen in starting material will be determined, the benefits of clean starting material will be demonstrated, and epidemiological data obtained to set health standards for starting material. We will also examine the feasibility of novel methods to produce high-health planting material as a second-line defence, and examine the potential for resistance deployment where we think this may be feasible.

The primary aim of the project is to improve the management/control of high priority bacterial diseases of horticultural crops primarily through the use of starting material with appropriate health standards based on sound epidemiological data and by best-practice recommendations to achieve those standards.

The project and core objectives are structured around several of the high-priority host-pathogen combinations, in each case developing and applying the approaches that are most likely to lead to practical improvement in disease control for growers within the shortest timescale.

The selected host-pathogen combinations also serve as model crops and we believe will serve as examples of approaches that can be extended across a broader range of crops. An over-riding theme of this proposal is to obtain the data that can be used to set or define health standards for starting material that can support a 'clean-start' approach to disease control.

Core objectives:

Demonstrating best practice for Brassicas and Xanthomonas campestris pv. campestris (Xcc)

• Case study at a farm with recent and on-going issues to determine the role of different potential infection sources
• Produce and demonstrate the value of high-health seeds and transplants

 Resistance and epidemiology of spear rot

• Determine availability of resistance in current commercial varieties
• Determine the role/importance of seed-borne and transplant-borne inoculum on disease levels in the harvested crop
• Determine rate of pathogen spread during plant raising

 Herbs and Pseudomonas bacterial blight

• Determine the prevalence of the bacterial blight pathogens Pseudomonas syringae apii and coriandricola in coriander and parsley seed

 Cherry laurel and shot-hole

• Case studies on two holdings to determine the prevalence of the pathogen on stock plants and/ bought-in plant material
• Investigate the potential value of micro-propagated stock plants to provide high-health propagation material
• Determine the rate of pathogen spread under different growing conditions

Ivy and Xanthomonas leaf spot

• Case study to determine the prevalence of the Xanthomonas hortorum hederae on bought in plant material
• Determine the rate of pathogen spread under different growing conditions.

 Geraniums/Xanthomonas

• Case studies to determine the prevalence of Xanthomonas hortorum pelargonii on geranium propagation material, and other PO/herbaceous subjects.
• Determine the rate of spread during propagation

 Novel production systems

 Knowledge exchange

• Develop a general cost of control/intervention vs. loss model to demonstrate the benefit (or otherwise) of control interventions (e.g. seed testing, etc.) and potential losses