Prevention of root diseases in closed soiless growing systems by microbial optimization
1999
Postma, J. (DLO Research Inst. for Plant Protection, Wageningen (Netherlands)) | Os, E.A. van | Kritzman, G.
In soilless growing systems where nutrient solutions are recirculated, slow filtration is one of the methods to overcome problems with pathogen dissemination. This method eliminates pathogens, but does not destroy the entire natural microflora. The present study aims at a maximal elimination of pathogens and investigates the influence of the slow filtration method on the dynamics of the microflora. In a small scale filter system, pathogen elimination was influenced by the pH of the nutrient solution. The fungal pathogen Fusarium oxysporum was eliminated to a higher extent at pH 7 than at pH 5, whereas elimination of the bacterial pathogen Erwinia carotovora was better at pH 5 than at pH 7. In a greenhouse filter system, elimination of F. oxysporum was similar for the four different filter media used (i.e. fine sand, and three qualities of glasswool). The turbidity in the influent was higher than in the effluent. The other qualities of the nutrient solution were not influenced strongly by slow filtration. Different techniques to obtain quantitative and qualitative data about the microbial population, including diversity, have been compared. Bacterial numbers (i.e. plate counts) before and after slow filtration were roughly the same. Numbers of fungi, which were around the detection limit, probably decreased by the slow filtration. In general, numbers of specific groups of bacteria did not change significantly by slow filtration. However, a clear shift of the bacterial community in their ability to use several carbon sources was measured with BIOLOG. Also the molecular fingerprints (PCR-DGGE) of the bacterial populations before and after slow filtration were distinctly different. The type of filter medium did not influence the bacterial populations according to any of the methods described.
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