Increased soil suppressiveness to Fusarium wilt of flax after addition of municipal solid waste compost

The suppressiveness of a loamy soil amended with municipal solid waste compost to Fusarium wilt of flax (caused by Fusarium oxysporum f. sp. lini) was studied. The soil was moderately conducive to the disease, with an estimated half life time (HLT) of the flax population of 41 days. Heat-treatment made the soil highly conducive (HLT of 28 days). Compost addition increased the suppressiveness of the control soil, proportionally to the application rate (10, 20 and 30%). Heat-treated compost was as effective as control compost in inducing the suppressiveness in the control soil (HLT of 103 and 97 days, respectively). Heat-treated soil amended with control compost and control soil amended with heat-treated compost were incubated before infestation with the pathogen, in order to allow the microflora of the control component to colonize the heat-treated component. Incubation had no marked effect on the suppressiveness of the mixtures. Both microflora of soil and compost were involved in the suppressiveness and mainly acted through nutrient and space competition towards the population of the pathogen.