Cryopreservation of entrapped monoxenically produced spores of an arbuscular mycorrhizal fungus

Abstract

A study was conducted to quantify the ability of entrapped, monoxenically produced spores of an arbuscular mycorrhizal fungus to germinate and reproduce the fungal life cycle after cryopreservation. No germination was obtained after incubation of entrapped spores in glycerol and mannitol and subsequent cryopreservation at -70 °C, regardless of the concentration of cryoprotectants and duration of incubation. Incubation for 1 d in 0.5 M sucrose, and for 1 and 2 d in 0.5 M trehalose, led to spore germination after cryopreservation at -70 °C. Lower cryopreservation temperatures were tested with entrapped spores incubated for 1 d in 0.5 M trehalose. The highest germination rate, estimated by the percentage of potentially infective beads (%PIB), was obtained at -100 °C. A %PIB of 95% (water agar medium) to 100% (Strullu-Romand medium) was obtained at this temperature. Thereafter, %PIB rapidly decreased at -140 and -180 °C. Heavy sporulation and high internal root colonization were obtained after re-association of the entrapped spores, incubated for 1 d in 0.5 M trehalose and subsequently cryopreserved at -100 °C, with transformed carrot roots. This demonstrates the ability of entrapped spores to reproduce the fungal life cycle following cold treatment.

Keywords: alginate beads; arbuscular mycorrhizal fungi; cryopreservation; entrapment; monoxenic culture; trehalose.