Effects of short-wavelength ultraviolet ray irradiation on the early development and induction of pigmentation mutants of conchospore germlings in Pyropia haitanensis (Rhodophyta)

Ultraviolet mutagenesis is a safe and efficient method to induce mutations for breeding new germplasm of laver. In this study, high-frequency short-wave ultraviolet (UV-C) irradiation (lambda = 254 nm) with different doses (50, 100, 200, 300, 400 and 500 J m(-2)) was used to induce colour mutants during the germination of conchospores in Pyropia haitanensis. The early development of conchospore germination and the morphogenesis of tetrad germlings were observed, which revealed that low-dose irradiation (50 J m(-2)) promoted the germination and early development of conchospores, while irradiation doses above 100 J m(-2) inhibited the germination of conchospores and growth of tetrad germlings. In the dose range of 50-500 J m(-2), the survival rate and germination rate of conchospores gradually decreased, while the mutation rate of colour mutants increased first and then decreased with increasing doses. The highest mutation rate was observed with the dose of 300 J m(-2) or with irradiation time 72 s. These results indicated that the optimal UV-C irradiation dose was 300 J m(-2) for the mutagenesis of P. haitanensis conchospores. In addition, UV-C irradiation also had a significant effect on the early development of conchospores and phenotypes of pigmentation mutant arranged in tetrad germlings, which was mainly manifested in the large number of colour-sectored blades produced by irradiated conchospores and in the decrease in their aspect ratios. This study provides new insights in carrying out UV-C mutagenesis for the breeding of P. haitanensis.