The self-regulatory potential of agro-ecosystems: Using nematodes as indicators for legume disease suppressive soils

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The susceptibility of legumes to root-rot diseases has massively contributed to the decline of their production area in Europe since 1974. This affects the biological nitrogen fixation as well as the overall sustainability of agroecosystems. As pesticides are of limited use to control soil-borne diseases, in the long term the build-up and maintenance of disease suppressive soils is much more promising. For the development of sustainable agricultural systems, there is a need to identify means by which to increase disease suppressiveness on the long run. Furthermore, robust and easy-to-apply indicators for disease suppressiveness of soils need to be identified.In two long-term experiments of the University of Kassel (since 2010 and 2011), soil suppressiveness to root-rot pathogens of pea was increased already after four years of minimum tillage (<12 cm depth) combined with compost fertilization compared to plough tillage (25-30 cm) combined with mineral potassium and phosphorous fertilization. In addition, specific cover crops suppressed plant-parasitic nematodes. Furthermore, free-living nematodes, which play an important role in disease suppression, were increased by minimum tillage. However, little is known about the use of free-living nematode trophic groups as indicators for disease suppressiveness of soils. Five years after these initial results, the long-term experiments at the University of Kassel are an important resource to investigate the development and stability of disease suppressiveness of soils as well as the role of free-living nematodes in disease suppression. We hypothesize that1. Specific nematode functional groups are linked with disease suppressiveness of soils;2. Minimum tillage and compost enhance disease suppressiveness of soils3. Cover crops foster specific nematode functional groups and thus, soil disease suppressiveness.In work package 1 (WP1), free-living nematodes will be identified and quantified in four differently managed soils of the long-term experiments applying morphological and molecular (NGS/OTUs) methods. Species composition and abundance will be related to nutrient contents as well as microbial biomass and activity of the respective soils. In a greenhouse experiment (WP2), specific suppressiveness of the soils against the plant-parasitic nematode Pratylenchus penetrans will be tested on peas and linked with abundances of nematode functional groups that were identified in WP1. In WP3, soils will be tested for their general suppressiveness against soil-borne fungal pea pathogens while the effects of cover crops on nematode taxa associated with disease suppression (WP1-3) will be determined via qPCR in WP4. Interrelationships of soil management histories, physico-chemical soil properties, specific and general suppressiveness, and nematode functional groups will be analysed using multivariate statistical approaches in order to obtain new and easy-to-apply indicators for disease suppressive soils.