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.

本研究旨在探究原生性捕食性真菌——卵寄生菌属的 Hyalorbilia oviparasitica（原称 Dactylella oviparasitica）及其相关菌种，是否与加利福尼亚地区曾种植过十字花科植物的土地中糖芥根结线虫（Heterodera schachtii）的抑制现象相关。通过在经高压蒸汽灭菌和未经灭菌的土壤样本中种植 H. schachtii 的宿主植物，感染 H. schachtii，并在经过两代线虫后计数雌性 H. schachtii 的数量，以确定这些土壤中生物性 H. schachtii 抑制作用的程度。通过将经高压蒸汽灭菌土壤中每克新鲜甘蓝根中的 H. schachtii 雌虫数量与未经灭菌土壤中的数量进行比值计算，得出抑制作用的量。此外，通过两种方式研究了 H. schachtii 抑制作用的量与 H. oviparasitica 及其相关真菌的种群密度之间的关系。分析结果表明，抑制线虫作用最强的四种土壤，其真菌种群密度也最高，且在所有测试土壤中，H. schachtii 抑制作用的水平与这些真菌之间存在显著的正相关关系。