Effect of management strategies and rotation on plant-pathogen suppression by soil microbial communities

Enhancement of disease suppressive properties of soils limits disease development and is, as a result, essential for sustainable agriculture. Moreover, it can be a profitable strategy for farmers to manage diseases with lowered levels or without pesticides. Agricultural soils differ in their suppressiveness towards soil-borne plant pathogens, which can be attributed to soil type, organic matter content, as well as by management practices such as crop rotation, tillage and fertilization. The objective of the current research is to devise management strategies supporting disease suppression based on the response of pathogen-suppressing soil microbial communities. A field trial is being conducted to test experimentally the effect of crop rotation and management treatments on crop health and yield, as well as the suppressive response of the soil and its physical, chemical and biological properties. An experimental site with an on-station field trial with a winter-wheat rotation in the North of France has been selected. Soil samples are taken twice in the cropping seasons of winter wheat in 2012 and 2013. Soil suppressiveness is tested in bioassays with three different soil-borne pathogens in winter wheat under controlled environmental conditions. Biological targets which are assumed to provide complementary information on soil quality and diseases suppressive capacity of soil have been selected: 1) fungal and bacterial diversity and community structure, being important quality parameters of soil life; 2) arbuscular mycorrhizal fungi (AMF), obligatory mutualistic symbionts that supply plants with inorganic nutrients and protect them against diverse abiotic and biotic stresses; 3) Lysobacter spp., a recently described antagonist that correlates with soil suppressiveness in Dutch soils; 4) community structure of nematodes, expressed as maturity index, proposed as indicator for soil quality. A preliminary consideration of the results so far shows a variable response to crop sequence and management for bacterial and fungal, AMF, and nematode communities. Some limited changes in disease suppression were detected. Lysobacter spp. is present in the selected field, but is not influenced by the soil treatments. Correlation between the treatments and the different measurements will be performed when all samples have been analysed (i.e. mid 2013