4.1. Hyperparasites of plant-parasitic microfungi

Plant-parasitic microfungi are frequently colonized by hyperparasitic fungi that are able to penetrate the hyphae, the spores, and/or the reproductive structures of their fungal hosts (Gams et al., 2004; Lumsden, 1992; Zhan et al., 2014). Some of these parasites are specific to certain groups of plant pathogens and have garnered interest as biocontrol agents, such as Ampelomyces quisqualis(Dothideomycetes: Pleosporales) (Fig. 7), a naturally occurring hyperparasite of powdery mildews (Faticov et al., 2022; Huth et al., 2021). The most common plant-parasitic hosts include species of powdery mildews (Erysiphaceae), black mildews (Meliolales), tropical tarspot fungi (Phyllachorales), rusts (Pucciniales), and smuts (Ustilaginales and further orders) (Gams et al., 2004; Hawksworth, 1981). Information about hyperparasitic fungi on plant-parasitic microfungi is scattered through literature, and there is no detailed treatment of biotrophic plant pathogens and their hyperparasites, as most publications deal with individual groups of fungi (Bermúdez-Cova et al., 2022). Therefore, the following sections offer a summary of hyperparasites attacking these major groups of plant pathogens.