Effects of mesophilic and thermophilic composts on suppression of Fusariumroot and stem rot of greenhouse cucumber

Three composts were tested for their ability to suppress root and stem rot caused by the soil borne fungal pathogen Fusarium oxysporum f. sp. radicis- cucumerinum (FORC) on cucumber. Two of the composts were prepared from sepa rated dairy solids either by windrow (WDS) or vermicomposting (VMC) while t he third, obtained from International Bio-Recovery (IBR), was prepared from vegetable refuse using aerobic digestion. Three sets of potting mixes were prepared by mixing the composts with sawdust at varying ratios, and seeded with cucumber cv. Corona. After 14 days of growth in the greenhouse, inocu lum of FORC (20 mL of 5 x 10(6) micro-conidia per mL) was applied to each p ot at three different times (14, 21, and 35 days). In unamended inoculated pots, the pathogen caused stunted growth and reduced flowers. Amendment of WDS in the potting mix suppressed these symptoms, while VMC and IBR had no effect. All three composts reduced the FORC colony forming units (cfu) at t he end of the experiment (10 weeks). There was a large increase of fluoresc ent bacteria near the vicinity of roots particularly in WDS amended potting mixes. When water extracts of the composts were plated onto acidified pota to dextrose agar (APDA), only IBR contained a potent thermostable inhibitor to FORC. This inhibitor was removed by activated charcoal but was not part itioned into petroleum ether at acid, basic, or neutral pH. Inhibition of F ORC by IBR was not due to electrical conductivity or trace elements in the compost. Contrasting effectiveness of the WDS and VMC made from the same wa ste suggests that composting method can influence the disease suppression p roperties of the finished compost.