Cryopreservation of in vitro-produced Rhizophagus species has minor effects on their morphology, physiology, and genetic stability

Cryogenic storage is considered to be the most convenient method to maintain phenotypic and genetic stability of organisms. A cryopreservation technique based on encapsulation-drying of in vitro-produced arbuscular mycorrhizal fungi has been developed at the Glomeromycota In Vitro Collection. In this study, we investigated fungal morphology (i.e., number and size of spores, number of branched absorbing structures (BAS), hyphal length, and number of anastomosis per hyphal length), activity of acid phosphatase and alkaline phosphatase in extraradical hyphae, and variation in amplified fragment length polymorphism (AFLP) profiles of in vitro-produced isolates of five Rhizophagus species maintained by cryopreservation for 6 months at -130 A degrees C and compared to the same isolates preserved at 27 A degrees C. Isolates were stable after 6 months cryopreservation. Comparing isolates, the number of BAS increased significantly in one isolate, and hyphal length decreased significantly in another isolate. No other morphological variable was impacted by the mode of preservation. Phosphatase activities in extraradical hyphae and AFLP profiles were not influenced by cryopreservation. These findings indicate that cryopreservation at -130 A degrees C of encapsulated-dried and in vitro-produced Rhizophagus isolates (i.e., Rhizophagus irregularis, Rhizophagus fasciculatus, Rhizophagus diaphanous, and two undefined isolates) is a suitable alternative for their long-term preservation.