Hyphae of waxcap fungi colonise plant roots

• Our hypothesis: waxcaps follow a biotrophic mode.
• In our study we sought molecular and histological evidence for this hypothesis.
• We detected DNA material and waxcap hyphae in forb roots.
• Conclusion: Hygrocybe s.l. is an endophytic fungus, at least temporarily.

The trophic strategy of the globally distributed waxcaps (Hygrophoraceae) is uncertain. Some clues point to a biotrophic mode, particularly the 13C and 15N (stable isotopes) signatures. The observation of dense basal hyphae of Hygrocybe fruit bodies being tightly attached to live fine roots may be indicative of a plant-derived nutritional habit. To further scrutinize this fungus–plant association, stipe base samples and attached plant fragments were examined histologically. Waxcap hyphae were found growing inside live fine roots of associated vegetation. Amplification and sequencing of waxcap DNA from living root tissues using species-specific PCR primers also confirmed their presence in live plant roots. We therefore conclude that this group of fungi has a biotrophic lifestyle with plants.