Fig. 4

Pathogenicity of Polydomus karssenii DSM 106825 towards nematode cysts and eggs. a Symptomatic cysts of Heterodera filipjevi obtained from in vitro pathogenicity tests, exhibiting black eggs infected by the fungus. b Highly melanised running hyphae of Polydomus karssenii growing in cyst mucilage within the cysts cavity. c–e Fungal-infected eggs of Heterodera filipjevi: c Naturally occurring egg from field collected cyst samples infested by Polydomus karssenii (image from Helaly et al. (2018a), d Infested egg obtained from a cyst infected by the fungus during incubation on the fungal colony during in vitro tests, e Early stage of fungal colonisation observed in slide culture studies. Note deformation of the body cavity of the developing juvenile. f–h Fungal infected eggs of Heterodera schachtii: f Fungal infected egg obtained from a symptomatic cyst incubated on the fungus during in vitro pathogenicity tests; g, h In vitro infection process of Polydomus karssenii in nematode eggs: direct penetration of the fungus through the egg shell (indicated by arrows) and growing inside the body cavity of the developing juvenile (g), Development of the fungus inside the nematode body forming thick-walled moniliform hyphal cells (h). Bars = 0.6 mm (a), 30 µm (b–d, f), 20 µm (e), 50 µm (g, h)