Cold storage of adult thalli for archeospore-based seed-rearing in Neopyropia yezoensis aquaculture

Red seaweed Neopyropia yezoensis ranks among the most economically significant marine crops. When under wound stress, the gametophytic thalli of N. yezoensis release large amounts of asexual archeospores which will develop into individual thalli afterwards. Thalli direct seeding system based on archeospores, being able to circumvent the complicated conchocelis cultivation, was therefore a promising seeding strategy in nori aquaculture industry. Usually, thalli harvesting is in March and seed-rearing, however, is in September. Preservation of adult thalli for 5–6 months is required for producing archeospores. In this study, we optimized the cold storage procedures for N. yezoensis adult thalli to achieve efficient archeospore production for practical application in nori aquaculture. We found dehydrated thalli exhibited significant higher cellular viability than those immersed in cryoprotects after 4 months of cold storage. Then we investigated the effects of water loss rates, sucrose pretreatment, cold acclimation and thawing temperature on both cell viabilities and archeospore production. Besides, immediate cutting thalli into small fragments after thawing achieved better efficiency of spore production than days of recovery culturing. We finally implemented the optimized protocol to store 30 g of adult thalli for 4 months and released archeospores at a commercial seeding facility. These archeospores attached to a seedling net (2.0 m × 9.0 m) at a density of 24–30 spores on each millimeter of rope and successfully germinated into morphologically intact seedlings after marine culture. The establishment of this technology will be helpful in promoting the application of archeospore-based thalli direct seeding system in nori aquaculture. • Optimized the protocol of long-term cold storage for Pyropia adult thalli. • Efficient archeospore production was achieved after 4–6 months of cold storage. • Practical application of the cold storage protocol at commercial seed-rearing facility.