Novel means for variety breeding and sporeling production in the brown seaweed Undaria pinnatifida (Phaeophyceae): Crossing female gametophytes from parthenosporophytes with male gametophyte clones

The unialgal haploid gametophyte clones are frequently used for variety breeding and sporeling production in the brown seaweed Undaria pinnatifida because a single crossing of a pair of the selected male and female gametophyte clones can generate sporophytic offspring with identical genotype and phenotype. As the seeds to be sprayed on the collectors, the detachment rate of the filamentous gametophytes is high in comparison to the seeded spores. In this investigation, we report the use of parthenogenesis to achieve the same goal in variety selection and sporeling production but with higher efficiency. The selected female unialgal gametophyte clone (Code: 06‐8‐1F) was induced to produce parthenosporophytes. These sporophytes were grown up in a controlled system and used to release zoospores. All zoospores generated into female gametophytes. These female gametophytes were allowed to go through parthenogenesis for the second year to confirm the applicability of this means. In the third year, the zoospores released from the parthenosporophytes were seeded on collectors over summer in female gametophyte form. In the early autumn, a selected male unialgal gametophyte clone (code: 5#F1‐2‐5M) was used to cross the seeded female gametophytes on the collectors. When the sporelings reached a mean length of 780 μm, they were transplanted to open sea on longlines for growing up. At harvest, the average length, width and wet weight of the adult sporophytes were 211 cm, 48.8 cm and 373 g, respectively. The sporophytic blades were uniformly smooth without wrinkles on both sides of the midrib, indicating top quality of the products. Amplified fragment length polymorphism analyses confirmed the identical genotypes of sporophytic offspring. These results suggested that this novel variety breeding and sporeling production method could serve as an efficient alternative to the traditional breeding technique for U. pinnatifida and possibly other commercial kelps that have identical life cycles.