ISHS Acta Horticulturae 554: World Congress on Soilless Culture: Agriculture in the Coming Millennium
IMPORTANCE AND CHARACTERIZATION OF THE BIOLOGICAL COMPONENT IN SLOW FILTERS |
| Authors: | T. Brand, W. Wohanka |
| Keywords: | Slow filtration, efficacy, bacteria, biofilm |
| Abstract:
In closed irrigation systems plant pathogens might be spread through circulating nutrient solution. Disinfecting nutrient solution before reuse can prevent this. Slow filtration is a feasible way to eliminate pathogens. The mode of action is a combination of different mechanisms. To determine the contribution of biological factors, the efficacy of sterilized slow filters were compared with biologically activated filters. Biologically activated slow filters were significantly more effective than sterilized filters against Xanthomonas cam-pestris pv. Pelargonii, 98.47 % compared to 68.79 % for sterilized nutrient solution and 80.39 % for sterilized NaCl-solution. There was no difference between biological acti-vated and sterilized filters against Fusarium oxysporum f.sp. cyclaminis using nutrient solution (88.78 % and 87.18 %, respectively). Highest efficacy against microconidia was achieved with NaCl-solution (98.76 %). Quantitative investigations bacteria populations in slow filters showed a typical vertical distribution. Highest densities between 107 and 108 CFU cm-3 were found in the top layer, decreasing rapidly within the first centimeters to 106 CFU cm-3 and remaining at this level in deeper layers. Qualitative studies of 635 isolates from different layers of slow filters were conducted by means of MicroStation™ System (BIOLOG) and FAME-analysis (MIS, Microbial ID). Only 7.7 % of the tested isolates could be identified congruently by both systems. Pseudomonads (Pseudomonas, Comamonas, Burkholderia, Xanthomonas) were detected as the most abundant group of bacteria to be identified. Studies of bacterial colonization of filter media sand and rockwool were conducted using scanning electron microscopy. Microcolonies were the typical form of colonization on sand. In contrast, in rockwool a biofilm between the fibers was found. | |
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