Book of Abstracts
11th IFOAM Scientific Conference
11-15 August 1996, Copenhagen, Denmark
1) University of Kassel, Division of Ecological Agriculture, Nordbahnhof: 1a, D-37213 Witzenhausen; 2) Hesse State Board for Regional Development and Agriculture, Kölnische Str. 48-50, D-34117 Kassel; 3) University of Göttingen, Institute for Plant Pathology, Grisebachstr. 6, D-37777 Göttingen
Investigations on suppressive effects against soil borne plant pathogens of yard waste- (YWC), biogenic waste- (BWC) and cattle manure compost (CMC) were aimed both to demonstrate the potential of these composts and describethe role of involved biological mechanisms. Composts were produced under standardized systems and subsequently evaluated for their suppressiveness towards Pythium ultimum Trow. and Phytophthora parasitica by bioassays applying several hosts (pea, cucumber,tomato) and growing media. Determination of the microbial activity (Hydrolysis of Fluoresceindiacetat (FDA)), microbial biomass (fumigation-extraction) and population density of P. ultimum (selectiveagar media (SA-PCNB)) were used to characterize composts. Treatment of P. ultimum inoculated sterilised sand and nonsterilised peatgrowing media with YWC and BWC resulted in a significantly increased fresh matter yield and a reduction of the disease incidence by 30-50% in allhost-pathogen systems. Cattle manure compost showed such results only occasionally. Comparisons of nonsterilised and sterilised composts (gamma-irradiation) on suppression of P. ultimum prove the extraordinary importance of biological mechanisms involved. Nevertheless microbial activity of YWC, BWC and CMC amended sterilised sand related to fresh matter yield of peas did not result in a correlation. Calculating the specific activity (rate of FDA-Hydrolysis per unit microbial biomass), however, we found a good relationship to fresh matter yield (r = 0.742**). Contrary to CMC, both YWC and BWC show a high level of specific microbial activity which is comparable to the high metabolic potential of the microorganisms in competition with pathogens for easily available carbon sources. This results in fungistatic effects towards P. ultimum demonstrated with YWC treated peat growing media (50 %v/v) compared to pure peat growing media.
In order to introduce suppressive composts into biological control systems further studies are needed particularly in the questions of compost production and -storage and the establishment of predictive methods for disease suppression.