The use of water extracts from composted organic waste to suppress crop diseases has particular potential in developing countries and small-holder agriculture where resources are limited. These extracts can be produced by low-cost, non-aerated methods to prepare “non-aerated compost tea” and previous studies have shown that application can lead to reduction of a wide range of foliar and soil borne diseases in horticultural crops.
The bacteria Ralstonia solanacearum is a major pathogen of potato in many regions of the world and there are few successful control methods. Glasshouse trials were conducted in Ethiopia to examine if non-aerated compost teas could reduce disease and what influence various factors had on the degree of efficacy. These included production factors (i.e. compost type and resulting microbiological and physico-chemical properties), application factors (timing of application, concentration) and the addition of adjuvants. In this experiment, compost teas made from agricultural waste compost were more effective to reduce disease severity than those made from solid municipal waste or vermicompost tea. Moreover, application of NCT at the same time that potato tubers were planted and inoculated with pathogenic R. solanacearum led to greater disease reduction than when applied 7 days before or after introducing the pathogen inoculum. The most effective treatment resulted in a 2.5-fold reduction in disease compared to the non-treated controls, based on the “area under the disease progress curve” parameter. In a second glasshouse trial, the addition of myrrh gum led to the greater reduction of disease severity than compost tea alone.
Next-generation sequencing of 16S and ITS genes for bacterial and fungal communities in compost tea, and physico-chemical characteristics will be presented which provide a basis to explore differences in disease suppression efficacy.