Components of soil suppressiveness against Heterodera schachtii

Heterodera schachtii populations were introduced into nematode-suppressive and conducive field plots and were monitored for 2550 degree-days (DD). At 1200 DD, H. schachtii population densities significantly increased in conducive versus suppressive plots, up to 14-fold at termination of the trial. In greenhouse experiments with the same soil, H. schachtii female population densities were similar in suppressive and conducive soil in the first nematode generation, but remained low in the suppressive soil compared to significant increase in conducive soil in the second generation. At termination of the experiment, ca. one third of the cysts, but no females from suppressive soil were infested with fungi, whereas fungal-infested females and cysts were rarely found in conducive soil. The most common fungi isolated from infested cysts were Fusarium oxysporum, Fusarium sp. nov., and Dactylella oviparasitica. Paecilomyces lilacinus and some non-identified fungi occurred less frequently. Suppressiveness was transferred at a rate of one cyst from suppressive soil amended to 110 g of H. schachtii-infested conducive soil. Heat treatment of suppressive soil for 30 min at 55°C eliminated H. schachtii suppressiveness and reduced F. oxysporum populations to the detection level.