<p>  </p> <p>Plant-parasitic nematodes are amongst the most important pathogens impacting crops. Potatoes and soybean are vital crops for rural livelihoods and essential for food security, but their cyst nematode parasites remain a significant constraint globally. <em>Globodera</em> and <em>Heterodera </em>species are amongst the most damaging and internationally recognized quarantine pests of these crops, causing up to 80% yield loss. Their second stage juveniles (J2s) penetrate the host plant root tips and establish a residence close to the vascular bundle from where they extract nutrients as they complete their life cycle. Restrictions of control chemicals have led to an urgent need for alternative control strategies for cyst nematodes. Biological control is a promising alternative control measure, and fungi possess many characteristics that could make them great biological control agents of cyst nematodes. Most nematode populations are thought to be regulated by their natural enemy community. It is unclear which fungi are best adapted as natural enemies of these parasites and how they might do this. This project aimed to (a) characterize and compare the mycobiome diversity of cyst nematode species; (b) isolate and characterize fungi associated with potato and soybean cyst nematodes (c) screen isolated fungi for their efficacy as biocontrol agents against cyst nematodes; and (d) describe any isolated fungi identified as new and having potential for cyst nematode antagonism. Cyst populations were collected from different regions and screened for fungi using culture-based methods. For our next-generation sequence data analysis, we found differences in fungal community assemblages between center of origin of the potato cyst nematode (Peru; South America) and the regions where these nematodes were introduced such as Europe and North America.  There was no significant difference in fungal community assemblages of cysts collected between the years 2019 and 2020. We characterized fungi associated with the cyst nematodes and found that the most frequently isolated genera were <em>Fusarium, Penicillium, Cylindrocarpon, Phoma, Aspergillus </em>and<em> Verticillium</em>. Filtrates from <em>Trichoderma</em> sp. 2, <em>Alternaria alternata, </em>and <em>Fusarium acaciae-mearnsii </em>were toxic on SCN eggs while <em>Purpureucillium lilacinum, Fusarium proliferatum</em> and <em>Aureobasidium</em> <em>ellingtonae </em>sp. nov. were toxic on PCN eggs and juveniles. A new species of <em>Aureobasidium</em> isolated from the potato cyst nematode (<em>Globodera ellingtonae</em>) for the first time, and having biocontrol potentials against this nematode, was also identified, and described. </p>