The soybean cyst nematode (SCN; Heterodera glycines) is the most economically consequential pathogen of soybeans worldwide. Although biological control of SCN was proposed decades ago, only a few products are available on the market. Mining for new fungal biological control organisms and evaluating their potential to enhance integrated management of SCN is crucial. In this study, we evaluated 20 candidate biological control organisms in vivo that were selected out of a culturable mycobiome of over 5000 isolates based on their performance in in vitro assays. Of these isolates, labelled A through T, we identified three isolates, one Ilyonectria sp. (D), and two Purpureocillium sp. isolates (E and T), that significantly reduced SCN reproduction on a susceptible soybean variety (Sturdy) inoculated with both high and low levels of SCN eggs, compared to an untreated control, in a growth chamber cone-tainer assay. In a greenhouse pot assay, Purpureocillium isolates E and T also controlled nematode reproduction better than an untreated control and performed on par with the commercial fungal biological control agent, MeloCon (R) WG, which was applied at 41-fold higher concentration. In a second greenhouse assay, with higher nematode numbers, only isolate E performed as well as MeloCon (R) WG. This research identified promising candidate biological control agents of SCN that are as or more effective than existing products at much lower spore inoculation levels.

Fungal biological control of soybean cyst nematodes (SCN) is an important component of integrated pest management for soybean. However, very few fungal biological control agents are available in the market. In this study, we have screened fungi previously isolated from SCN cysts over 3 years from a long-term crop rotation field experiment for their ability to antagonize SCN using (i) parasitism, (ii) egg hatch inhibition, and (iii) J2 mortality. We evaluated egg parasitism using an in-vitro egg parasitism bioassays and scored parasitism using the egg parasitic index (EPI) and fluorescent microscopy. The ability of these fungi to produce metabolites causing egg hatch inhibition and J2 mortality was assessed in bioassays using filter-sterilized culture filtrates. We identified 10 high-performing isolates each for egg parasitism and toxicity toward SCN eggs and J2s and repeated the tests after storage for 1 year of cryopreservation at −80°C to validate the durability of biocontrol potential of the chosen 20 isolates. Although the parasitic ability changed slightly for the majority of strains after cryopreservation, they still scored 5/10 on EPI scales. There were no differences in the ability of fungi to produce antinemic metabolites after cryopreservation. [Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

The cyst of the soya bean cyst nematode (SCN; Heterodera glycines), an economically important pathogen of soya beans worldwide, represents a unique microhabitat in soil. The fungi inhabiting cysts may include natural antagonists of the SCN as well as saprotrophs and other opportunists. This study aimed to characterise the entire culturable mycobiome of SCN cysts obtained from a long-term soya bean-corn rotation experiment using ITS fungal barcoding. Fusarium was consistently the most frequently isolated taxon across all sampling time points and crop sequences, followed by Ilyonectria. Among fourteen genera frequently isolated from SCN cysts, five fell within the single family Nectriaceae (Sordariomycetes) and five within the order Pleosporales (Dothideomycetes), suggesting independent evolutionary origins and shared adaptations in these groups towards colonisation of SCN cysts. Six genera (Pochonia, Clonostachys, Fusarium, Neonectria, Alternaria, and Leptosphaeria) varied significantly by crop sequence in at least one year.