Fungal Community Analysis of Californian Soils Cropped to Brassica species and Heterodera schachtii Females Derived from those Soils

The goal of this study was to determine whether indigenous populations of the nematophagous fungus, Hyalorbilia oviparasitica (formerly Dactylella oviparasitica) and related fungi, were associated with suppression of the sugarbeet cyst nematode (Heterodera schachtii) in Californian soils previously cropped to Brassica species. Experiments to determine the amount of biological H. schachtii suppressiveness in these soils were performed by planting a H. schachtii host crop in autoclaved and unautoclaved portions of each soil, infesting them with H. schachtii, and then counting the number of H. schachtii females after two nematode generations. The amount of suppressiveness was calculated by dividing the number of H. schachtii females per gram of fresh cabbage roots from the autoclaved soils by those from the unautoclaved soils. The relationship between the amounts of H. schachtii suppressiveness and the population densities of H. oviparasitica and related fungi was examined in two ways. These analyses showed that the four soils with the highest amounts of nematode suppressiveness also had the highest population densities of these fungi, and that there was a strong positive correlation between the levels of H. schachtii suppressiveness and these fungi across all of the tested soils.