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Prevention of root diseases in closed soilless growing systems by microbial optimisation, a replacement for methyl bromide

Contract nr: FAIR-CT98-4309
Project nr: 4309
Project type: SC
Starting date: 01/03/1999
Duration: 48 months
Total cost: 1,787,128 EUR
EC Contribution: 1,205,368 EUR
Scientific Officer: Richard HARDWICK
Research topic: Plant health

Closed soilless growing systems have significant advantages: conservation of scarce water resources, no leaching of nutrients and pesticides and improved quality of products. Disadvantages of the system are rapid dispersal of soil-borne pathogens by the recirculating nutrient solution and accumulation of potential phytotoxic metabolites. Active disinfection with high-tech equipment suppresses or destroys the natural microflora. Recent research has demonstrated a natural suppressiveness by the resident microflora against colonisation by pathogens. Equally, passive disinfection with slow (sand) filtration has shown that the resident microflora is not destroyed, while elimination of some of the most harmful pathogens can be achieved. A combination of optimising the natural suppression and passive disinfection will lead to a sustainable technologically-simple system, which is also inexpensive and robust.

The objective of the project is to develop a sustainable system for the prevention of root diseases in closed soilless growing systems in greenhouses, by microbial optimisation. The sustainable system may replace the soil-grown system, in which the soil fumigant methyl bromide is used in Southern Europe and the run-to-waste soilless system in Northern Europe.

To achieve this sustainable system, the following steps have to be taken: diseased conditions and in relation to active and passive disinfection methods; healthy and diseased conditions and, again, in relation to the disinfection method techniques need to be elucidated to improve the efficacy of the method. These three steps provide the basic information on the sustainable concept of disease suppression in closed systems. The results will be used in the next step: to enhance the microbial suppression of two root pathogens (Phytophthora cryptogea, Pythium aphanidermatum) by stimulation and management of the natural presence of the resident microflora. The final step will be to inform commercial growers and suppliers of the results by demonstration of the sustainable system via open days, a workshop and publication in technical and scientific journals. The research will be carried out on major crops in protected cultivation (tomato, cucumber and gerbera). The final outcome will be a sustainable soilless system which can be adopted in Northern and Southern Europe, whereby water resources are managed effectively, pesticide use is minimised and replaced by nonchemical treatments, and the environment is protected in the long-term.

Current situation/results:
In the first year, experiments in cucumber, tomato and gerbera have been executed to optimise and standardise detection techniques of microflora, present in the nutrient solution, and of metabolites, released by plant roots or microorganisms. Additionally, slow filtration experiments have been taken place to optimise the layout of the filter. Now it can be said that for slow filtration there is no preferential filter medium. All the media tested (fine filter sand, "local" sand, glasswool, two types of rockwool and polyurethane foam) showed no significant differences after inoculation with the fungus Fusarium oxysporum and the bacteria Xanthomonas campestris. A similar result was obtained for the filtration rate (100 and 300 l.m-2.h-1). Choice of the filter medium should be made on other bases, such as investment, transport and handling. These experiments were executed in cucumber and gerbera. In the same crops, samples were taken to find which groups of microflora were present during cropping and which detection method (plate count, fatty acid, BIOLOG, DGGE) is most suitable to detect them. Equally, samples were taken from a tomato crop. Samples were also taken to detect the lowest possible concentration. With plate counts, a certain limit exists, but with PCR and nested-PCR a lower detection limit can be achieved. The method was optimised for Pythium aphanidermatum and Phytophthora cryptogea. A dipstick technique was being optimised to detect the latter pathogens, but variable results were obtained. Metabolites were tested in low and high concentrations on tomato seedlings. In general it could be said that low concentrations improved growth, while high concentrations were toxic.
Preparations were made for testing microbial suppression of Pythium aphanidermatum and Phytophthora cryptogea while the recirculating nutrient solution is treated with passive disinfection (slow filtration at which the natural microflora keeps alive), active disinfection (UV radiation, the solution is sterilised) and a reference without any treatment. These tests will be executed again in cucumber, tomato and gerbera.


Erik Arthur VAN OS
Institute of Agricultural and Environmental Engineering (IMAG)
Mansholtlaan 10-12
NL-6700 AA Wageningen
Tel.: +31 317 47 63 16
Fax: +31 317 42 56 70


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    Sveriges Lantbruksuniversitet
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    Universita' degli Studi di Torino
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