ABSTRACT
Despite numerous preventative measures, the hairy roots syndrome is an increasing problem in greenhouse horticulture. A recent survey of 177 tomato, cucumber and eggplant growers in Flanders (Belgium) revealed an increase of this disease in the last two years, with about 26% of all the tomato crops showing the syndrome. In this study, we compared the physicochemical and microbial community characteristics of inorganic and organic growing media in relation to the presence of the causative agent of the hairy roots, the plant pathogen Agrobacterium rhizogenes. We aimed to identify how the microbial and environmental interactions influenced the development and spread of this disease in a soilless cultivation system. Multivariate statistical analysis performed to assess the characteristics of each growing media revealed key variables impacting the hosted microbial community. Thus, humidity, pH, potassium and conductivity were drivers of the differences among microbial community composition. High throughput sequencing analysis of the bacterial family abundance of the communities present in organic media indicated potential competitive interactions with A. rhizogenes. Based on our hypothesis that growing media hosted a particular microbiota with potential for modulating hairy roots, we determined how the environment in organic media is reshaped to avoid establishment of A. rhizogenes. Our methodology provides a comprehensive insight into the complex bacterial interactions in horticultural media, which may be potentially applied for the development of effective control strategies and decrease in economic losses.
