SPREAD OF PHYTOPHTHORA CACTORUM AND VERTICILLIUM DAHLIAE BY SLOW SAND FILTRATION TREATMENT OF THE RECIRCULATING NUTRIENT SOLUTION ON CLOSED SOILLESS GROWING SYSTEMS IN STRAWBERRY

The microflora present in the nutrient solution of a closed soilless growing system (CSGS) is important for the suppression of root pathogens. In this experiment, the slow sand filtration (SSF) treatment was used on strawberry (Fragaria × ananassa Duch.) plants grown in CSGS to assess its efficacy for reducing the dispersion of Phytophthora cactorum and Verticillium dahliae propagules. A randomized complete block design with three replicates was performed. Each replicate consisted of a 6 meter hanging cultivation line with 65 strawberry plants (var. Camarosa) per line cultivated with CSGS by SSF independent. Two growth media were used: composted cork thin waste mixed with rice hulls (1:1 v:v) ratio (CCR) and peat substrate (P). P. cactorum and V. dahliae dispersion in CSGS was studied by the detection of propagules in recirculating nutrient solution and in growth media. P. cactorum propagules were measured by a plant baiting technique. V. dahliae propagules were measured by filtration of recirculating nutrient solution. The density of Verticillium dahliae propagules from growth media samples was estimated by the wet-sieving technique and plate counts on semi-selective media. Based on community level physiological profiles, different community structures were evident between growth media evaluated Eco-microplates (Biolog Inc.; Hayward, Calif.) were used to determine differences in physiological abilities of the microbial communities from different growth media and the similarities between these communities and the pathogen. The number of P. cactorum propagules in the disinfected solution was eliminated by SSF. The number of V. dahliae microsclerotia of growth media recovered by the wet sieving technique was higher in the inoculated than in the non inoculated zone of the line. The similar catabolic potential of CCR microbial communities and Verticillium dahliae, suggests a high competition for C-sources.