A COMPARATIVE STUDY OF THREE CRYOPRESERVATION PROTOCOLS FOR EFFECTIVE STORAGE OF IN VITRO-GROWN MINT (Mentha SPP.)

This study was designed to determine the response of diverse mint genotypes to three commonly used cryopreservation techniques. Four mints [Mentha x piperita nothosubsp. citrata (Ehrh.) Briq.; M. canadensis L.; M. australis R. Br, and M. cunninghamii Benth] were cryopreserved using three protocols: controlled rate cooling (CC), encapsulation dehydration (ED) and PVS2 vitrification (VIT). Regrowth of mint species following controlled rate cooling (93%) was significantly (P<0.0001) better than encapsulation dehydration (71%) and vitrification (73%). All four genotypes responded well to the controlled rate cooling protocol but there was some variability with the other two protocols. Genotype specific response to the individual protocols showed that there were significant differences in the recovery of Mentha x piperita nothosubsp. citrata and M. australis with CC> VIT> ED. There were also significant differences in the recovery of M. cunninghamii and M. canadensis, with CC and ED significantly better than VIT. Regrowth of the shoot tips of these mints ranged from 60 % to 95 % for all but one treatment. The overall results of this study compare favorably to other techniques. These improved results may be due to a combination of favorable growth conditions, cold acclimation and recovery medium. Controlled rate cooling was the most successful technique for the storage of these diverse mint genotypes; however recovery of shoot tips from VIT and ED was high and these techniques could also be used for cryogenic storage of mint germplasm