Abstract:In order to develop a new variety of Pyropia with thin blade, which is suitable for cultivation in the aquaculture areas with high temperature along the coast of South China, the blades of the wild-type strain(PC-WT) of Pyropia chauhanii were irradiated with 60Co-γ rays and cultured at a high temperature(30℃) for 25 days, and then the improved strain of PC-M was obtained. Subsequently, PC-M was compared with PC-WT for high-temperature resistance, growth, contents of major photosynthetic pigments, the releasing ability of monospores and conchospores. The results showed that the rates of survival, division and rhizoid germination of conchospores were not significantly different between PC-M and PC-WT at 18 and 23℃, but the survival rates were 250.7% and 305.4% higher, the division rates were 42.4% and 67.1% higher, the rhizoid germination rates were 86.6% and 175.3% higher in the former than those in the latter at 27 and 29℃, respectively. The F1 gametophytic blades of PC-M and PC-WT were cultured at 23℃ for 30 days and then cultured at 18, 23, 27 and 29℃ for another 10 days, in the group of 18, 23 and 27℃, the absolute growth rates of PC-M blades were 5.1, 5.3 and 7.5 times those of PC-WT, and the specific growth rates were 1.3, 1.3 and 1.8 times those of PC-WT, respectively. The apical and middle parts of PC-WT blades were disintegrated because of releasing a large number of monospores after being cultured for 15 days at 27℃ and 10 days at 29℃, and only the basal parts of the blades remained intact. On the other hand, PC-M blades grew rapidly with normal color and shape without releasing monospores, just slightly curled after being cultured for 30 days. In addition, the contents of three major photosynthetic pigments(chl. a, PE and PC) and the conchospore numbers in PC-M at a suitable temperature(23℃) were 39.4%, 209.8%, 94.8% and 36.7% higher than those of PC-WT, respectively. Meanwhile, the thickness of blades of PC-M was 31.6% thinner than that of PC-WT. The above results indicated that PC-M has thinner blade, higher contents of the major photosynthetic pigments, faster growth speed, higher-temperature resistance, larger number of conchospore release and no monospore release as compared with PC-WT. It is therefore potential to be developed into a new variety suitable for cultivation along the coast of South China.