In vitro mycorrhization of pear (Pyrus communis)

The Mycelium Donor Plant system (MDP) was adapted to study the time course of the colonization of Pyrus communis by Rhizophagus irregularis under in vitro conditions. Isolated germinated spores did not colonize pear roots. Inoculum composed of R. irregularis spores/mycelium associated with chicory root fragments was used to inoculate Medicago truncatula which became thereafter the MDP of pear plantlets. Typical intraradical structures (hyphae, arbuscules, spores/vesicles) and appressoria were observed in the pear roots. During acclimatization, the pear plants formed a densely branched root system. R. irregularis colonization not only altered the root architecture but also changed the nutrient composition of the acclimatized pear plantlets

Extraradical mycelium network of arbuscular mycorrhizal fungi allows fast colonization of seedlings under in vitro conditions

Actively growing extraradical hyphae extending from mycorrhizal plants are an important source of inoculum in soils which has seldom been considered in vitro to inoculate young plantlets. Seedlings of Medicago truncatula were grown in vitro in the extraradical mycelium network extending from mycorrhizal plants. After 3, 6, 9, 12, and 15 days of contact with the mycelium, half of the seedlings were harvested and analyzed for root colonization. The other half was carefully transplanted in vitro on a suitable growth medium and mycelium growth and spore production were evaluated for 4 weeks. Seedlings were readily colonized after 3 days of contact with the mycelium. Starting from 6 days of contact, the newly colonized seedlings were able to reproduce the fungal life cycle, with the production of thousands of spores within 4 weeks. The fast mycorrhization process developed here opens the door to a broad range of in vitro studies for which either homogenous highly colonized seedlings or mass-produced in vitro inoculum is necessary