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Biofumigant Crops as Replacements for Methyl Bromide Soil Sterilisation in Sustainable Strawberry Production

Dates: 2006-2010
Funding: Defra LINK
Countries: UK
Scientific Collaborators: East Malling Research (EMR)
Henry Doubleday Research Association (HDRA)
Industrial Collaborators: East Malling Trust for Horticultural Research (EMT),
Hugh Lowe Farms Ltd (HLF), Hall Hunter Partnership (HHP), KG Growers Ltd (KG), Marks & Spencer PLC M&S), Farm Advisory Services Team Ltd (FAST), Horticultural Development Council (HDC), Plant Solutions Ltd (PSL), East Malling Ltd (EML), Berry World Ltd (BW)
NRI Project Leader: David Hall

BACKGROUND

strawbwilt© University of Greenwich

UK strawberry production has an ex-farm value of £118M and is expanding rapidly to meet rising consumer demand. Production is 95% soil-based and a lack of virgin land is a problem for both conventional and organic growers. The most important soil borne disease is caused by the fungus Verticillium dahliae, which is capable of causing significant crop and economic losses (right). Effective control of V. dahliae can only be achieved by soil sterilisation resulting in the widespread use of methyl bromide to sterilise soil used for strawberry production. Methyl bromide will be banned from use in 2008 and this poses a huge threat to productivity. Other chemical controls, such as chloropicrin and dazomet, are less effective and it is uncertain how much longer their use will be permitted or acceptable to the consumer. Steam sterilisation is being considered, but is currently uneconomic and energy inefficient for most soil types. In organic production systems soil sterilisation by chemicals or steam is not an option. Development of strawberry varieties with increased disease resistance could provide a long-term solution, but resistance tends to be pathogen and cultivar specific. 'Elsanta', a disease prone variety, is currently favoured by supermarkets for both conventional and organic sales and this is unlikely to change in the medium term. What is needed in the short to medium term is an alternative to chemical soil sterilisation that is reliable, has a high level of efficacy, is.environmentally benign, is acceptable to the consumer and can be incorporated into standard farming practice, including organic production. Biofumigation, based on the process of using plant-derived volatile chemicals to supress soil borne diseases, has such potential.

OBJECTIVES

Experiments will be designed to screen anti-pathogen effects of plant material from diverse plant families against V. dahliae using laboratory bioassays. The most promising will be taken forward into fully replicated field trials. Isothiocyanates or other agents that have an impact on the pathogenic fungi will be identified and loss of pathogen viability quantified against the specific molecules. The rate of release and persistence of chemicals from the most promising biofumigant crops will be measured. Molecular techniques will be used to profile species in amended and unamended soil to determine the impact of biofumigants on non-target beneficial microrganisms (i.e. those associated with improving soil fertility). The interaction between the resident microbial community and the effect of the biofumigant crop will be considered. The agronomy of the biofumigant crops in relation to strawberry production will be developed using fully factorially designed field experiments.

RESULTS

biofum1© University of Greenwich

Ten potential biofumigant crops were screened in laboratory trials for their effects on reducing soil populations of V. dahliae. These included several brassica species known to produce isothiocyanates (ITCs), sudan grass, onion, lavender and the soil amendment, BioFence. The brassicas showed a good effect, but the most effective was lavender. Chemicals given off by the plant residues were characterised. These included ITC's but also large quantities of several sulphides and monoterpenes from the lavender. Field trials are in progress to compare effects of Brassica juncea, Sinapis alba and BioFencein both conventional and organic plots (right).

 

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