Critical Moisture Content Windows Differ for the Cryopreservation of Pomelo (Citrus grandis) Seeds and Embryonic Axes

Cryopreservation was attempted using a partial dehydration and freezing protocol on pomelo (Citrus grandis) seeds of ten cultivars and embryonic axes of one cultivar collected from Xishuangbanna. Although seeds of all ten cultivars could be dehydrated safely to 10% moisture content, further dehydration impaired seed viability with critical moisture contents ranging from 9% to 7%. Complete seedling regenerated from seeds frozen in a moisture window between 5-9%, and maximum seedling recovery varied between 22-86%. Cryopreservation of Jiajieyou cv. embryonic axes had a moisture window between 3-20%, much wider compared to whole seed cryopreservation, and maximum post-thaw emergence of 93% was achieved at 13% moisture content. Emergence differed only slightly from survival when whole seeds were cryopreserved, but for the embryonic axis cryopreservation at low moisture contents resulted in much lower emergence than survival. Possible causes of intraspecific variation in cryotolerance in pomelo seeds is discussed.