Selection and characterization of a high-temperature resistant strain by hybridization recombination in Pyropia yezoensis

In this paper, a crossing-experiment of intraspecific hybridization in Pyropia yezoensis was done for breeding improved strains. The male parent was the red mutation strain (TM-18), which was characterized by red blade, fast growing, high contents of photosynthetic pigments and with resistance to high temperature, and the female parent was the green mutation strain (OMO-1), which was characterized by green blade, slow growing, low contents of photosynthetic pigments and poor resistance to high temperature. An improved strain (TW-9) was finally selected from the recombinant F₁ blades. TW-9 strain showed some different characters from the parental strains. The result showed that at normal temperature (18 °C) and high temperature (24 and 25 °C) for 13 days of post-culture, the survival rates of conchospores in TW-9 strain were 1.0, 1.1, and 1.1 times those of TM-18 strain, and were 1.1, 4.7, and 7.2 times those of OMO-1 strain, respectively. At 18 °C, the abnormal rates of conchospore germlings had no significant difference between different strains, but at 24 and 25 °C, as compared with TM-18 and OMO-1 strains, the abnormal rates of conchospore germlings in TW-9 strain reduced by 20.3% and 29.5%, and by 78.4% and 69.5%, respectively. When the conchospore germlings (40-day-old, at 18 °C) were cultured at 18, 24 and 25 °C for another 10 days, the absolute growth rates of TW-9 strain were 0.9, 1.5 and 0.8 times those of TM-18 strain, and were 1.4, 1.5 and 28 times those of OMO-1 strain, respectively. In addition, after being cultured at 24 °C for 25 days or at 25 °C for 10 days, OMO-1 strain blades decayed badly to complete disintegration. However, the blades of TM-18 and TW-9 strains were curl slightly when being cultured at 24 °C for 25 days, and TM-18 blades were decay badly to complete disintegration at 25 °C for 15 days, while TW-9 blades were only decay slightly at 25 °C for 30 days. After being cultured at 18 and 24 °C for another 15 days, the phycobiliprotein contents of TW-9 strain were 61.5 and 77.8 mg/g which was almost the same to the TM-18 strain, and were 1.4 and 1.4 times those of OMO-1 strain, respectively. After being cultured at 18 °C for 55 days, the blades thickness of TW-9 strain was 25.6 μm, which was reduced by 13.5% and 17.7% compared with those of TM-18 and OMO-1 strains, respectively. Besides, there was no significant difference in quantity of conchospores released between the three strains. These results indicated that TW-9 strain has similar characteristics to TM-18 strain, such as fast growing, high contents of photosynthetic pigments and great quantity of conchospores released, as well as thinner blade and better high-temperature resistance, and its color is close to the wild-type, which could meet the demands for productive cultivation. Therefore, TW-9 strain is expected to become a superior new strain of P. yezoensis.