Factors affecting appressorium development in the vesicular–arbuscular mycorrhizal fungus <i>Glomus mosseae</i> (Nicol. &amp; Gerd.) Gerd. &amp; Trappe

SUMMARY Investigations on the luck of appressorium formation in the roots of the non‐host plant Lupinus albus L. showed that root exudates do not inhibit mycelial growth of the vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. &amp; Gerd.) Gerd. &amp; Trappe, but that they hinder hyphal attachment and fungal recognition of roots. Exudates do not stimulate hyphal proliferation in the rhizosphere. G. mosseae hyphae were able to recognize and attach to excised root of both lupin and host plants, forming swellings resembling apressoria. No growth of G. mosseae hyphae was observed around simulated roots consisting of nylon, silk, polyamide and glass threads, whereas appressoria were formed on heterologous hyphae of VAM fungal species. The hypothesis that a purely thigmotropic stimulate could trigger hyphal attachment and the further differentiation of appressoria was excluded.