Effects of developmental age on cryopreservation and cold storage of seeds of <i>Arundina graminifolia</i> , a classic Dai medicinal orchid

BACKGROUND: Arundina graminifolia is a traditional medicinal plant of the Dai people in China. To enhance its ex situ conservation greater knowledge is needed on the species’ seed storage behavior, particularly the effects of developmental age, moisture content and temperature and storage time on seed survival (germination). OBJECTIVE: To investigate whether A . graminifolia seeds can be preserved using conventional seed banking and/or cryopreservation in relation to seed developmental age and lipid thermal fingerprinting. MATERIALS AND METHODS: Naturally pollinated and artificially pollinated capsules at three maturity stages were collected (i.e., six seed lots), equilibrated to 15%-75% relative humidity (RH), and stored at 4°C, −20°C and in liquid nitrogen (LN). Seed quality, including after 3 and 6 months of storage, were evaluated using asymbiotic germination. Seed water and lipid thermal properties were determined by differential scanning calorimetry. RESULTS: Seed maturity state was confirmed by the moisture content decrease of fresh seeds as well as the lipid transition enthalpy increase (from c. 10 to 20 J g -1 DW) and melting peak temperatures of dry seeds. Immature seeds (either as green capsules [GC] or 60 days after pollination [DAP60]) had some level of desiccation sensitivity (up to germination halving) and significant losses of germination during storage. Mature seeds (from capsules just before dehiscence [JBD], fully dehisced [FD], DAP90 and DAP120]) retained high germination levels under the vast majority of RH x Temperature x Time combinations. DSC analysis of the enthalpy of transitions during cooling and warming revealed that seeds equilibrated to ≤ 75% RH were below the unfrozen moisture content. CONCLUSION: Mature seeds of A . graminifolia seem to have orthodox seed storage behaviour, and both cold storage and cryopreservation appear feasible for the long-term ex situ conservation of this species.