Evaluation of an improved strain of Porphyra yezoensis Ueda (Bangiales, Rhodophyta) with high-temperature tolerance

The red algae Porphyra yezoensis has high commercial and nutritional value; however, its cultivation and product quality are jeopardized by global warming. Screening of high-temperature-tolerant strains would greatly reduce cultivation risks and benefit the Porphyra industry. Single somatic cells isolated enzymatically from the wild-type (WT) blades irradiated by ⁶⁰Co-?? rays were screened at 25°C; one strain, T-17, displayed significant high-temperature resistance. Further culture studies showed that conchospore germlings of T-17 showed 76.2% survival at 23°C and 65.7% survival at 24°C, while the WT conchospore germlings survived at significantly lower percentages of 16.9% and 11.5%, respectively, over a period of 16 days. Furthermore, T-17 conchospore germlings divided at higher percentages of 100% at both 23 and 24°C compared to the WT conchospores with 99.8% and 81.8%, respectively. When the 50-day-old F₁ gametophytic blades were transferred from the optimal temperature of 18°C to high temperatures of 23 and 24°C, the T-17 blades sustained growth over a 45-day period without rot, and their mean lengths increased by 20 and 4.2 times, respectively. The mean lengths of WT blades only increased by a factor of 0.6 and 0.4 times and were severely decayed after being cultured for 15 days at high temperatures. The mean wet weights of T-17 blades increased by 418.9 and 195.3 times, but only 7.8 and 4.6 times in WT at 23 and 24°C, respectively. These results indicate that T-17 is superior to WT in growth and high-temperature tolerance, which may offer a new cultivar for the nori industry as a high-temperature-resistant strain to counteract the effects of global warming.