Isolation and characterization of an improved strain of Porphyra chauhanii (Bangiales, Rhodophyta) with high-temperature resistance

Abstract

The blades of the wild-type strain of Porphyra chauhanii (PC-WT) were irradiated with ⁶⁰Co-γ rays and cultured at high temperature (30 °C) for 25 days. The surviving somatic cells of the irradiated blades were isolated enzymatically and were regenerated into whole blades and screened at high temperature. Vigorously growing blades at high temperature were selected and individually proliferated. A genetically homozygous and free-living conchocelis strain of TR-5 was obtained through parthenogenesis. Subsequently, TR-5 was compared with PC-WT for high-temperature resistance, growth, contents of major photosynthetic pigments, and the releasing ability of monospores and conchospores. The results showed that the survival percentage, division, and rhizoid germination of conchospores were not significantly different between TR-5 and PC-WT at 18 and 23 °C; but the survival percentages were 261.2 and 329.3 % higher, the division percentages were 42.8 and 72.6 % higher, and the rhizoid germination percentages were 94.3 and 199.5 % higher in the former than in the latter at 27 and 29 °C, respectively. When F₁ gametophytic blades of TR-5 and PC-WT were firstly cultured at 23 °C for 30 days, and then cultured at 18, 23, and 27 °C for another 10 days, the absolute growth rates of TR-5 blades were 4.4, 4.3, and 10.4 times those of PC-WT and the relative growth rates were 1.1, 1.1, and 2.0 times those of PC-WT, respectively. The apical and middle parts of PC-WT blades were disintegrated due to the release of a large number of monospores after culturing for 15 days at 27 °C or 10 days at 29 °C, and only the basal parts of the blades remained intact. On the other hand, TR-5 blades grew rapidly with normal color and shape without releasing monospores and were slightly curled, even after being cultured for an additional 30 days. In addition, the contents of three major photosynthetic pigments (chlorophyll a (Chl. a), phycoerythrin (PE), and phycocyanin (PC)) and the conchospore numbers in TR-5 at a suitable temperature (23 °C) were 66.7, 244.2, 115.7, and 92.0 % higher than those of PC-WT, respectively. Meanwhile, the blades of TR-5 were 23.2 % thinner than those of PC-WT. The results indicated that TR-5 has thinner blade, higher contents of the major photosynthetic pigments, faster growth speed, higher temperature resistance, has larger number of conchospores released, and no monospore release as compared with PC-WT. It therefore has potential to be developed into a new variety suitable for cultivation in the aquaculture areas with high temperature in the coast of South China.