Abstract
The dispersion of soilborne plant pathogens could be greater in closed soilless growing systems than in open ones. Theeffect 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 recirculatingnutrient 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.
Highlights
Closed soilless growing systems offer several advantages over those that use soil
The density of V. dahliae propagules in the drained solution storage tank of the three soilless growing systems revealed no effect of the system used in either the first or second crop cycles (Table 1)
The density of V. dahliae propagules in the drained solution storage tank and the filtered solution storage tank of the closed with slow sand filtration (CSSF) system did not differ significantly (Table 2)
Summary
Closed soilless growing systems offer several advantages over those that use soil. The use of the irrigation effluents in soilless growing systems may represent savings of up to 20% in water and fertilizers, in addition to avoiding subsoil contamination (Van Os et al, 2004). The surviving microflora collaborates with the disinfecting action in closed soilless growing systems with slow sand filtration (Van Os et al, 2004). A number of techniques have been developed for the disinfection of recirculating nutrient solutions These can be active, such as UV treatment (Runia, 1994a), heat treatment (Runia et al, 1997) and ozonification (Runia, 1994b), or passive, such as slow sand filtration (SSF) (Wohanka, 1995). Several studies have shown that SSF removes Pythium spp. and Phytophthora spp. propagules (Wohanka, 1995; Wohanka et al, 1999) In this regard, other authors have reported that the SSF and UV treatments are able to significantly reduce root rots caused by Phytophthora cryptogea (Garibaldi et al, 2003)
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