Isolation and characterization of a heat-resistant strain with high yield of Pyropia yezoensis Ueda (Bangiales, Rhodophyta)

A heat-resistant Pyropia yezoensis strain YZ-4 was isolated from the regenerated blades of single somatic cells of the wild-type (WT) blades treated with 60Co-γ-irradiation. When cultured at 23 °C and 24 °C, the survival and division rates of the YZ-4 conchospores were significantly higher than those of WT (P < 0.01). After 16 days in culture the survival rates of YZ-4 conchospores were 71.2% and 60.8% at 23 °C and 24 °C, respectively, and the division rates of the surviving conchospores were 100% in both cases. Under the same culture conditions, the survival rates of WT conchospores were only 16.9% and 11.5%, and the division rate 99.8% and 81.8% respectively. The resistance of 50-day-aged F1 gametophytic blades of YZ-4 to the temperature rebound was also significantly higher than those of WT (P < 0.01). After 30 days in culture at 18 °C, 23 °C and 24 °C, the mean blade length increased by 8.5, 4.3 and 2.3 times in YZ-4 and was only 3, 0.6 and 0.4 times in WT, respectively. The mean blade weight increased 191.9, 85.4 and 66.2 times in YZ-4, but only 78.2, 7.8 and 4.6 times in WT. On the 15th day WT blades began to decay, but no decay was observed in YZ-4 blades even after 45 days in culture at 23 °C and 24 °C. The results obtained indicate that YZ-4 has a higher resistance to higher temperature insults than WT and it might be of value for commercial production of P. yezoensis.