Cross Response of Slow Filters to Dual Pathogen Inoculation in Closed Hydroponic Growing Systems

The efficacy of slow filters for horticultural purposes is suggested to be the result of multiple factors. Physical and biological properties of the filter column and the nutrient solution are likely to influence on filter performance. It has previously been shown that enzyme activity on the filter skin is a main parameter which will explain roughly 50% of filter efficacy. Since enzyme activity is enhanced by the addition of fungal cell walls to the filter skin, presence of a fungal root pathogen might affect enzyme activity and filter efficacy. In this study, slow filters integrated into closed NFT systems with a tomato crop were inoculated with mycelia from Pythium aphanidermatum. Enzyme activity, microbial colonisation, polysaccharide content and DNA content of the filter skin as well as microbial flora and total organic carbon in the nutrient solution were monitored. Tests of filter efficacy against Fusarium oxysporum f.sp. cyclaminis showed no significant influence on filter efficacy by the addition of P. aphanidermatum. Enzyme activities in the filter skin were not affected by the addition of P. aphanidermatum. A negative correlation was found between biofilm polysaccharide content and activity of xylanase activity on the filter skin. Filter efficacy was high (>99.9%) throughout the study. No damage to the crop as effect of pathogenic fungi was seen. We concluded that abundance of an oomycete pathogen in a closed hydroponic system does not affect filter efficacy, and that the filter skin microflora function, but not composition, is affected by this pathogen.