PREVENTION OF ROOT DISEASES IN CLOSED SOILLESS GROWING SYSTEMS BY MICROBIAL OPTIMISATION AND SLOW SAND FILTRATION

Closed hydroponic systems are good alternatives for soil grown crops using methyl bromide in protected cultivation.
Root-infecting pathogens may be dispersed over the nursery by the circulating nutrient solution, which was reason to disinfect the nutrient solution.
The natural microflora in the nutrient solution will be destroyed by sterilisation and possibly loosing its suppressiveness against certain pathogens, while the use of slow filtration does not destroy the microflora.
In the present study it is the aim characterise the microflora and to investigate if a shift occurs after passing a slow sand filter.

Four sand filters were placed in four independent closed growing systems growing cucumber.
First influent and effluent of the sand filter were analysed, in later trials also the nutrient solution in stone wool slabs were analysed for microorganisms with plate counts, BIOLOG and DGGE.

Characterisation of the microflora with plate counts showed that numbers of total aerobic bacteria were similar or slightly lower after slow sand filtration.
Fluorescent pseudomonads, filamentous actinomycetes and fungi gave large differences between influent and effluent of the slow sand filters.
This is an indication for a shift in the natural microflora.
Also with BIOLOG and DGGE, such a shift in the microbial population was detected.

International Symposium on Chemical and Non-Chemical Soil and Substrate Disinfectation

E.A. van Os, J. Postma

growing media, hydroponics, disinfection, methyl bromide, cucumber, Pythium aphanidermatum, plate counts, BIOLOG, DGGE

https://doi.org/10.17660/ActaHortic.2000.532.10