Self-anastomosing ability and vegetative incompatibility of Tuber borchii isolates

In this work, different mycelial isolates of the ectomycorrhizal fungus Tuber borchii were analysed for their ability to form self-anastomoses, which were monitored by time-lapse live-cell imaging, providing a description of the anastomosis process. Self-fusions were evidenced in three out of five isolates, with frequencies ranging between 50 and 88% of hyphal contacts. Time-lapse video microscopy evidenced that during pre-contact events, hyphae were capable of growth re-orientation functional to hyphal contact: the time elapsed between hyphal growth re-direction and complete fusion ranged from 115 to 200 min. After anastomosis, protoplasmic flow occurred between fused hyphae and nuclei could be detected in fusion bridges. Vegetative incompatibility was also assessed by analysing macroscopic and microscopic hyphal interactions between paired T. borchii mycelia. Both plate-pairing tests and microscopic analyses showed vegetative compatibility only within the same isolate, whereas different degrees of incompatible responses were observed in inter-isolate pairings. The diversity of T. borchii strains revealed by cytomorphological approaches is consistent with their genetic diversity obtained by molecular methods.