Studies on Cryo-preservation of Registered Strains of Lentinula edodes

摘要

New strain needs to maintain desirable characteristics for long term when it was bred, but in lapse of time it degenerates into a bad condition. Therefore the influence of temperature on the viability and survival rates of Lentinula edodes strains were examined after cryopreservation. Also, liquid nitrogen preservation for L. edodes has been proved to be one of the most reliable method. However, a mechanical damage of strain is inevitable during cryopreservation of the fungus because the fungus is very sensitive to stress of cooling rate in the freezing process. So we tried to find out state change of L. edodes with a programmable freezer. L. edodes strains were preserved at -20 degrees C, -80 degrees C and -196 degrees C for 50 days. At -20 degrees C, its mycelial growth became extinct. When thawed, the growth of mycelia which were preserved at -80 degrees C was fastest. Attempts were made to investigate viability of L. edodes strains after freezing at -80 degrees C and -196 degrees C, respectively. As the result, more than 90% showed high survival rate of strains tested at -80 degrees C and -196 degrees C. Mycelial growth between apical and basal parts of colony after freezing preservation for 50 days was compared. At apical and basal parts, the survival rates showed 100% at -80 degrees C, but 98% and 94% at -196 degrees C, respectively. We confirmed that the ice crystal formation temperatures of L. edodes strains were -6.0 degrees C for Sanlim 1, -5.5 degrees C for the Sanlim 2, -4.0 degrees C for the Santim 3 and -15.5 degrees C for the Sanzo 302. These results indicated that L. edodes strains showed completely different responses to the ice crystal formation. We knew the fact that even the same species, especially L. edodes, they displayed completely different responses to the same freezing condition. Also, this has nothing to do with the connection between temperature type and freezing point. And a protocol was tried to minimize state change of L. edodes strains using programmable freezer when they are frozen, but it was not effective on them.