Excised embryonic axes from seeds of three taxa, namely, Citrus suhuiensis cv. limau madu, Citrumelo (Citrus paradisi x Poncirus trifoliate) and Fortunella polyandra, were desiccated in a laminar airflow, over silica gel, and ultra-rapidly. Desiccation sensitivity (WC50) was estimated for each taxon using the quantal response model. High desiccation tolerance (WC50 = 0.11 g water per g dry mass. g/gdw) was observed for limau madu embryonic axes desiccated in a laminar airflow and ultra-rapidly (WC50 =0.10 g/gdw). Desiccation tolerance was substantially lower (WC50 = 0.19 g/gdw) for silica gel dehydration. Similarly, high desiccation tolerance (WC50 = 0.15 g/gdw) was associated with F. polyandra embryonic axes when desiccated in a laminar airflow, while a lower desiccation tolerance (WC50 = 0.17 g/gdw) was observed with silica gel dehydration. Ultra-rapid desiccation led to the highest desiccation tolerance (WC50 = 0.14 g/gdw). The dehydration rate, however, had no influence on desiccation tolerance (WC50 ~ 0.14 g/gdw) for Citrumelo embryonic axes. After each desiccation period, embryonic axes were directly immersed in liquid nitrogen (LN) followed by rapid rewarming. Normal seedling recovery of 80 to 83% for excised embryonic axes of limau madu was observed for laminar airflow and ultra-rapid dehydration, but for silica gel dehydration, 57% recovery was obtained. Similarly, for Citrumelo, high recoveries of 100% and 97% were obtained from axes desiccated in a laminar airflow and using ultra-rapid dehydration, respectively, whereas a lower value was associated with silica gel dehydration (80%). For F. polyandra, 50% recovery was obtained both for laminar airflow and ultra-rapid dehydration, while much lower recovery (43%) was associated with silica gel dehydration. Regardless of the drying method employed, axis survival percentages following exposure to LN were commensurate with the desiccation sensitivity pattern.
To further understand the survival characteristics of desiccation-sensitive excised embryonic axes of Fortunella polyandra to desiccation and cryopreservation it is necessary to study the impact of drying rates on both the ultrastructure and electrolyte leakage.