Effect of soilless growing systems on the spread of Verticillium dahliae and the severity of the Verticillium wilt in strawberry

The dispersion of soilborne plant pathogens could be greater in closed soilless growing systems than in open ones. The effect of three soilless growing systems (open, closed and closed with slow sand filtration) on the dispersion of Verticillium dahliae propagules and the severity of the disease in strawberry (Fragaria × ananassa Duch.) has been analysed. V. dahliae dispersion in a closed system with slow sand filtration was studied by measuring propagules in the recirculating nutrient solution and in the growth medium. The growth medium used was coconut fiber. V. dahliae propagules were not removed by slow sand filtration. In the first crop cycle, an increase in the severity of Verticillium wilt was detected in the closed soilless growing system with slow sand filtration in comparison with the other two systems. This increase may be due to the non-elimination of V. dahliae propagules by filtration and to the lower microbial biomass in the filtered solution storage tank than in the drained solution storage tank. The decline in microbial biomass by filtration may improve the viability of the dispersed conidia, thus increasing the severity of the disease. This decline in microbial biomass by filtration may be compensated in the second crop cycle by the root debris from the first crop cycle. This debris may have provided nutrient sources to the microbes and increased the associated microbial biomass. Additional key words: microbial biomass, slow sand filtration.