Direct cryopreservation of winter-acclimated buds of Dracocephalum austriacum (Lamiaceae) from field material

This study develops protocols for the micropropagation and cryopreservation of Dracocephalum austriacum (Lamiaceae). It is a perennial herbaceous plant that overwinters with ground-level sprouts and is classified as critically endangered in Europe. In vitro cultures were initiated from seeds on growth-regulator-free Murashige & Skoog (MS) medium after nicking the seed coat. Propagation via shoot culture was achieved on ½ MS medium with 1 µM benzyl adenine (BAP). Rooting on various indole-3-butyric acid (IBA)-media was not reliable, but the rooting success was 80% after 10 weeks on medium with 1 µM BAP. Two starting materials underwent cryopreservation: (1) shoot tips from cold-acclimated in vitro plantlets and (2) axillary buds from winter shoots from field plants. For the cryopreservation of in vitro shoots, plant vitrification solution (PVS)3 and incubation over ice yielded the best results (~ 34% regeneration success). However, regeneration using winter acclimated buds were 100, 76 and 30% for collections in December, February and March, respectively, using the same protocol. Moreover, the ploidy levels of cryopreserved plantlets were estimated using flow cytometry. The use of winter-acclimated field material of temperate herbaceous plants or subshrubs has high potential as explant source for cryopreservation and calls for exploring this technique for other species.