Formation and growth of free-living conchosporangia of Porphyra yezoensis: effects of photoperiod, temperature and light intensity

Abstract

Porphyra are important economic seaweeds in Asia. New Porphyra breeding technology with free-living conchocelis was being developed to attempt to supplement or replace the primary method. It is crucial to regulate the entire course of conchocelis development exactly for new Porphyra breeding technology. In this research, laboratory culture studies were undertaken on the effects of external factors (photoperiod, temperature and light intensity) on free-living conchosporangia formation and growth in the Porphyra yezoensis HB line. The results showed that photoperiod, temperature and light intensity were very important factors affecting the formation and growth of free-living conchosporangia in P. yezoensis. Conchosporangial formation was found at all photoperiods; however, the ratio of conchosporangia to vegetative conchocelis increased with a decrease in the photoperiods. At 57 μmol photons m⁻² s⁻¹, the optimal light intensity with the highest conchosporangia formation rate was observed, and when the light intensity was 86 μmol photons m⁻² s⁻¹ or below 42 μmol photons m⁻² s⁻¹, the conchosporangia formation was inhibited. The optimum temperature for conchosporangia formation was 25 °C, and the free-living conchosporangia formation rate decreased with the decreased temperatures. Growth experiments showed that a temperature of 25 °C, a light intensity of 86 μmol photons m⁻² s⁻¹ and a photoperiod of 12 L:12 D were optimum for promoting the growth of conchosporangia. The present results contribute to the understanding of the factors that control the growth and development of free-living conchosporangia, laying an important foundation for controlling the development of free-living conchocelis and breeding with free-living conchosporangia.