Suppression of plant pathogens by organic extracts a review

This paper reviews the environmental and economic pressures which are leading towards the development of more 'sustainable' system of crop production. Such systems demand a holistic approach whereby inputs affect several aspects of the overall matrix. Adding organic extracts from seaweed to soils results in enhanced suppressivity, increased activity by species of micro-organism which are potent agents for biological control and may trigger the generalised or specific resistance processes within the plant. Results used as illustrations here show that organic extracts will encourage the growth of benign organisms (such as Pseudomonas putida), their capacities to form substances (such as siderophores) which reduce the metabolic efficiency of pathogenic organisms and extra-cellular enzymes (such as amylase, cellulase and glucanase) which in turn provide energy sources for the beneficial bacteria. This illustrates that more rational and scientific approaches based on research offers means to manipulate the host-pathogen complexes in favour of both crop productivity and environmental health.