Long-term survival after cryopreservation of the endangered exceptional species Crotalaria avonensis

Cryopreservation has been shown to be a viable alternative method of long-term storage for exceptional species which cannot be seed banked. While its use is gaining in popularity worldwide for plant conservation, its novelty translates into a dearth of literature on the long-term (>5 year) survival of species in cryo-storage. This study presents an assessment of survival across three variations on the encapsulation vitrification method for 3–16 years of cryostorage for shoot tips of the federally endangered exceptional plant species, Crotalaria avonensis. In addition, the more recently-developed droplet vitrification method was compared to encapsulation vitrification for short-term survival. Overall, over 92 % of banked genotypes survived after long-term cryo-storage, and the droplet vitrification method appears to improve survival over the original encapsulation vitrification procedures. In addition, the long-term survival data validate the previously published guidance that a 40 % initial survival after liquid nitrogen exposure will lead to a 95 % chance of survival after long-term storage, with 39 % initial survival in C. avonensis leading to a 95 % probability of survival after long-term storage per genotype. Initial survival after short-term liquid nitrogen exposure appears to be an indicator of long-term survival in storage, which can give practitioners some indication of their banking success. This study contributes to the literature showing the potential and success of using cryopreservation as a long-term banking method for threatened and/or wild exceptional species.