The significance of microbial diversity in agricultural soil for suppressiveness of plant diseases and nutrient retention
2000 - 2004
OBJECTIVES: This project aims to assess the importance of belowground bio-diversity as affected by agricultural practices, including crop type, for two life support functions in soil, i.e. nutrient retention and plant disease suppressiveness. APPROACH: It is hypothesized that a higher level of above ground bio-diversity will lead to a higher level of belowground diversity of microorganisms. Furthermore, the relationship between microbial diversity and the key functions of disease suppressiveness and nutrient retention are examined. Microbial communities, as well as disease suppressiveness and nutrient retention parameters, are examined from a long-term ecological research site in Wageningen, in which different crop management strategies are used. A permanent grassland system will be compared to a monoculture of maize and a crop rotation of maize. These field experiments are combined with soil/plant microcosm studies. PLANNING 2003: · Sampling bulk soil from the field (in May 2003) from 6 different treatments. The soil samples will be used for performing two microcosm experiments for soil suppressiveness with potato plants (cv. Desiree) and R. solani AG3. We will apply both culture dependant and culture independent methods to compare microbial diversity between different treatments. Special attention will be given to two bacterial groups- Pseudomonas and Bacillus. We will study antibiotic producing Pseudomonas population by applying three different sets of primers for detection phenazine, 2-4 diacetyl-phloroglucinol and pyronitrin. Furthermore we will apply a quantitative PCR (TAQMAN) for quantitative measurement of antibiotic production. · In September 2003 we will perform the last sampling from the field. Potato plants will be present in the plots under rotation. Assessment of the microbial diversity in the soils samples under different treatments will be performed. Diversity will be assessed by conventional plating techniques using media for total culturable bacteria, fluorescent Pseudomonas, Bacillus, Actinomycetes and total fungi. Diversity will also be assessed using molecular approaches, such as PCR-DGGE of extracted total DNA using universal and group specific primers. Additionally the soil suppressiveness against the soil-borne pathogen R. solani AG3 will be measured.