Seed and embryogenic callus cryopreservation of Thai rice (Oryza sativa L.) 'Hom Mali Daeng'

Thai rice landraces are a valuable heritage that must be conserved. A suitable protocol for seed and callus cryopreservation of Hom Mali Daeng rice was investigated. Seed cryopreservation experiments were divided into three groups as room temperature storage, gradient freezing by storage at 0 °C for 30 min, -20 °C for 30 min before soaking in liquid nitrogen, and direct immersion in liquid nitrogen. All groups were stored for 1, 3 and 5 months before germination and planting. The highest germination percentage was recorded in the control group after 3 months of storage, while highest growth performance was found in the direct freezing protocol after 5 months of storage. The vitrification technique was used for callus cryopreservation. Calli were exposed to plant vitrification solutions PVS2 and PVS3 for 0, 20, 40 and 60 min before immersion in liquid nitrogen for 24 h. After thawing and regrowth, cryopreserved calli were cultured on MS medium with 1 mg/L 1-naphthaleneacetic acid and 3 mg/L 6-benzylaminopurine for 6 weeks. Results revealed that cryopreserved calli from PVS3 for 0 min treatment (immediately immersed in PVS3 before transfer into liquid nitrogen) and PVS2 for 40 min provided high survival percentages at 100% and 75%, respectively. The vitrification system used in this report demonstrated an alternate cryopreservation approach for Hom Mali Daeng rice seed and callus, which can be subsequently adapted to other rice varieties.