Hyalorbilia oviparasitica Clade Detected in Field Soils Cropped to Sugar Beets and Enriched in the Presence of Heterodera schachtii and a Host Crop

The nematophagous fungus, Hyalorbilia oviparasitica and relatives (Hyalorbilia spp.), are known to parasitize several endoparasitic nematodes. In this project, we hypothesized that indigenous populations of this fungus could be used to predict nematode suppression in agricultural field soils. We quantified Hyalorbilia spp. in soil samples from 44 different sugar beet fields in the Imperial Valley of California. Seven soils harboring Hyalorbilia spp. and two that tested negative for the fungi were examined for nematode suppressive activity. Untreated and autoclaved portions of each soil were planted with cabbage and infested with sugarbeet cyst nematode (Heterodera schachtii) juveniles. Females and cysts of H. schachtii were enumerated after 12 weeks. In the seven soils harboring Hyalorbilia spp., females and cysts in the untreated soils were reduced by 61-82% compared to the autoclaved controls. Soils with no detectable Hyalorbilia spp. exhibited no nematode suppression. Two novel Hyalorbilia strains, HsImV25 and HsImV27, were isolated from H. schachtii females reared in field soil using an enrichment and double-baiting cultivation technique. Both strains suppressed H. schachtii populations by more than 80% in soil-based assays, confirming Hyalorbilia spp. are the likely causal agents of the nematode suppression in these soils. This study demonstrated that indigenous populations of a hyperparasite (Hyalorbilia spp.) in agricultural field soils predicted suppressive activity against a soilborne plant pathogen (H. schachtii). To our knowledge, it is the first report to demonstrate this capability. We anticipate this research will provide a blueprint for other similar studies, thereby advancing the field of soilborne biological control.

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Detection of Nematophagous Fungi fromHeterodera schachtiiFemales Using a Baiting Experiment with Soils Cropped toBrassicaSpecies from California’s Central Coast

Chen

Koike

Logan

et al. 2021

PhytoFrontiers™

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Until the early 1990s, cyst nematodes were abundant pathogens in fields where hosts of Heterodera spp. were frequent members of crop rotations along California’s Central Coast. To mitigate damage caused by Heterodera schachtii and H. cruciferae, the soil fumigant 1,3-dichloropropene (1,3-D) was used by more than 43% of surveyed broccoli growers. Over the last few decades, use of 1,3-D and other nematicides has dramatically diminished, suggesting a decline in nematode disease pressure. The goal of this study was to examine the hypothesis that increased population densities of nematophagous fungi contribute to the low populations of Heterodera spp. in fields frequently cropped to their hosts. In 2016, soil samples were collected from 152 Brassica fields with a broad geographical distribution, from Santa Barbara County to Santa Cruz County. The average number of Heterodera cysts per 250 cm3 of soil ranged from 0.5 to 27.5, with 62% of the soils harboring no detectable cyst nematodes and only a few samples reaching a potentially damaging threshold level. A baiting experiment with H. schachtii and cabbage was performed in a greenhouse to detect nematophagous fungi associated with nematode females as their posterior end emerged and became exposed to the soil’s rhizosphere. An Illumina-based sequence analysis of these H. schachtii females identified several known nematophagous fungi, including members of the Hyalorbilia oviparasitica clade, Pochonia chlamydosporia, certain Fusarium spp., and others. These soils clearly harbor a diverse population of hyperparasitic fungi that could be biologically suppressing cyst nematodes below a damaging threshold. [Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

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Hyalorbilia oviparasitica Clade Detected in Field Soils Cropped to Sugar Beets and Enriched in the Presence of Heterodera schachtii and a Host Crop

Cited by 4 publications

References 30 publications

Networks of free-living nematodes and co-extracted fungi, associated with symptoms of apple replant disease

Networks of free-living nematodes and co-extracted fungi, associated with symptoms of apple replant disease

Indigenous Populations of a Biological Control Agent in Agricultural Field Soils Predicted Suppression of a Plant Pathogen

Detection of Nematophagous Fungi fromHeterodera schachtiiFemales Using a Baiting Experiment with Soils Cropped toBrassicaSpecies from California’s Central Coast

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