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The goal of this study was to evaluate the use of passive bioreactors to reduce water-borne plant pathogens (Pythium ultimumandFusarium oxysporum) and nutrient load (NO−3and SO2−4) in greenhouse effluent. Sterilized and unsterilized passive bioreactors filled with a reactive mixture of organic carbon material were used in three replicates. After a startup period of 2 (sterilized) or 5 (unsterilized) weeks, the bioreactor units received for 14 weeks a reconstituted commercial greenhouse effluent composed of 500 mg L−1SO2−4and 300 mg L−1NO−3and were inoculated three times withP. ultimumandF. oxysporum(106CFU mL−1). Efficacy in removing water-borne plant pathogens and nitrate reached 99.9% for both the sterilized and unsterilized bioreactors. However, efficacy in reducing the SO2−4load sharply decreased from 89% to 29% after 2 weeks of NO−3-supply treatment for the unsterilized bioreactors. Although SO2−4removal efficacy for the sterilized bioreactors did not recover after 4 weeks of NO−3-supply treatment, the unsterilized bioreactor nearly reached a similar level of SO2−4removal after 4 weeks of NO−3-supply treatment compared with affluent loaded only with SO2−4, where no competition for the carbohydrate source occurred between the denitrification process and sulfate-reducing bacteria activity. Performance differences between the sterilized and unsterilized bioreactors clearly show the predominant importance of sulfate-reducing bacteria. Consequently, when sulfate-reducing bacteria reach their optimal activity, passive bioreactors may constitute a cheap, low-maintenance method of treating greenhouse effluent to recycle wastewater and eliminate nutrient runoff, which has important environmental impacts. [ABSTRACT FROM AUTHOR]

The water content of the growing medium and its interaction with a biocontrol agent was studied in a closed soilless culture system in order to identify factors that could increase the efficiency and decrease the variability of biocontrol agents. Pumice was chosen as the growing medium because of its high water-holding capacity and in view of the high water content required for the growth of the root pathogen. The commercial biocontrol agent BinabT (active strains Trichoderma polysporum and T harzianum) was evaluated at 50% and 70% water content. Studies were carried out in a controlled environment, in a climate chamber, using tomato as the model plant and Pythium ultimtim as the model pathogen. Pathogen levels were affected by the water content of the medium and the biocontrol treatment, while the amount of biocontrol agent was not affected by the water content of the growing medium. The Trichoderma strains in Binab T were able to reduce the amount of pathogen and the incidence of disease at both water contents tested. The biocontrol activity of Binab T against P. ultimum, as indicated by the level of glucanase production, was affected by variations in the water content of the growing medium. The pathogen, the biocontrol agent, and the water content of the growing medium, all had an impact on the microbial communities resident in the system. [ABSTRACT FROM AUTHOR]

Despite more than 50 years of research and their great potential for sustainable pest management, pathogen suppressive soils remain poorly understood. We conducted a study on suppression of root rot disease symptoms associated with Pythium ultimum in untreated and heat-sterilized soil from ten southern Swedish farms with six different cropping and management regimes. Physical and chemical soil properties, soil nematodes belonging to different trophic guilds, and the predominant soil oomycetes were analyzed for their potential as indicators of soil suppressiveness. Six of the ten sampled soils were suppressive to P. ultimum disease symptoms. Suppressive or conducive properties of the soils from sites with permanent soil cover were related to the presence of live soil biota, while soils from sites with interrupted soil cover had suppressive or conducive effects unrelated to live soil biota. In soils with biologically conducive effects, soils had high or low cation nutrient content, while biologically suppressive soils had intermediate nutrient levels. No relationship was found between disease symptoms and the soil nematode trophic community or the predominant soil oomycetes. Permanent soil cover and a balanced nutrient supply were correlated with biologically suppressive effects on P. ultimum disease symptoms. [ABSTRACT FROM AUTHOR]

Abstract: Because of the lack of high-quality water and the potential pollution of groundwater by leached nutrients, recirculation of nutrient solutions for greenhouse production is now unavoidable. Although closed growing systems offer several advantages from an environmental standpoint, the risk of pathogen dissemination is a major concern for growers. Constructed wetlands represent an ecological and low-cost alternative method for treating agricultural wastewaters. The objective of this study was to evaluate the effectiveness of three types of constructed wetlands for removing the waterborne plant pathogens, such as Pythium ultimum and Fusarium oxysporum, that can be found in greenhouse wastewater. The experiment was conducted in a greenhouse using three types of horizontal subsurface-flow constructed wetlands in eight replicates. The wetlands were filled with pozzolana, planted with common cattail (Typha latifolia) and supplemented with sucrose or compost carbon sources or left without an external carbon source. The wetland units received reconstituted greenhouse wastewater and were inoculated five times consecutively with P. ultimum and F. oxysporum at 106 CFUmL−1. Physical, chemical and biological properties as well as environmental parameters were evaluated during 12 weeks to characterize conditions related to plant pathogen removal efficiency. Even though 99.62–99.99% efficiency for pathogen repression was observed for the constructed wetlands, the compost amendment to the wetland promoted the development of biofilm around the filter media and the production of cell-wall degrading enzymes. Depending on the source of carbon that was provided to promote microbial population growth and wetland activity, different possible modes of action for pathogen removal were predominant but resulted in very high efficiency, considering that the wetlands were inoculated with massive populations of plant pathogens that are not found at the commercial level. This study showed that constructed wetlands can constitute an efficient and safe alternative to treat and then reuse greenhouse wastewater. [Copyright &y& Elsevier]