Successful initiation of sorus formation and viable zoospores in Ecklonia radiata on isolated lateral fronds under hatchery conditions

The critical first step to achieve the successful cultivation of Ecklonia radiata is the on-demand production of viable zoospores to seed culture ropes. However, the availability of zoospores from fertile field sporophytes is restricted to a narrow seasonal window. Therefore, the objective of this study was to develop a method to artificially induce the formation of sori to obtain viable zoospores. Firstly, we developed a method for the formation of sori under hatchery conditions and maintained individuals in different size groups under short- (8 h L:16 h D) and standard (12 h L: 12 h D) daylength. After 4 weeks, mature sori were present in all treatments and successfully released viable zoospores, which formed gametophytes and sporophytes with transition rates of up to 100%. Secondly, sori formation under hatchery conditions was compared to the natural population to ensure that the formation was genuinely driven by hatchery conditions. Individuals of E. radiata were maintained as whole individuals and isolated lateral fronds under short- and standard daylength for 4 weeks and their reproductive state was compared to sporophytes collected from the field at the beginning and end of the trial. Sori were formed faster and in significantly higher quantities on isolated fronds than whole individuals and more than 70% of all isolated fronds developed sori after 4 weeks. Crucially, all artificially induced sori released viable zoospores, while none were released from naturally formed sori. The developed method can be used to enable the year-round production of high quality sporelings of E. radiata.

Automated summary

This study successfully obtained viable zoospores of E. radiata through the method of artificially induced sorus formation, enabling year-round production of high-quality sporelings.