The have been a number of cases in the UK, USA and Europe in which outbreak of human disease has been attributed to consumption of vegetable or salad produce contaminated with bacteria such as E.coli O157:H7 and Salmonella. This has resulted in the need to understand factors which allow pathogenic bacteria to colonise and survive on fresh vegetables and salads, so that effective methods can be developed to ensure the safety of fresh produce.
The above ground parts of plants provide a home to diverse microorganisms including bacteria, fungi and protozoa, with the habitat termed the phyllosphere. Bacteria can be located on the leaf surface, but may also reside within the leaf itself, where they cannot be removed by disinfectants which are used to clean fresh produce prior to packaging. The microorganisms inhabiting the phyllosphere originate from nearby vegetation, the soil and the atmosphere, but microbes can also enter the phyllosphere following harvest in the field and during processing. The number and types of bacteria in the phyllosphere can be determined by a wide range of environmental variables, including rainfall, temperature and solar radiation. However, plant characteristics also play an important role indetermining the specific types of bacteria that can grow and survive in the phyllosphere, which can vary according to plant species and the age and position of leaves on the plant.
While much work has been conducted to understand how bacteria colonise leaves, and the localisation and survival of bacteria on the leaf surface, much less is known of the characteristics of the plant itself which allow bacteria to grow and survive in the phyllosphere. However, tools at Warwick HRI are available which for the first time would allow plant genes controlling the number, types and localisation of bacteria colonising the phyllosphere to be determined. The current project has two main aims. The first is to review the literature to determine current understanding of the relationship between plant genotype and phyllosphere bacterial populations, focussing particularly on the behaviour of human pathogens, and methodologies which are available to extend understanding of this topic. The second aim is to provide "proof of concept" that plant genotype controls phyllosphere bacteria, by determining the number and types of bacteria able to colonise 24 different lettuce types.
Following this work we would be in a position to know whether further work should be conducted to identify genetic loci controlling phyllosphere microbial populations. Ultimately the work will allow plant breeders to generate plant lines in which the phyllosphere bacterial community could be managed to reduce the risk of human pathogen survival in fresh produce, or to support bacterial populations beneficial to human health.