Intraspecific crossing of Saccharina japonica using distantly related unialgal gametophytes benefits kelp farming by improving blade quality and productivity at Sanggou Bay, China

Abstract

When cultivating the kelp, Saccharina japonica, in China, one of the causes leading to degeneration in blade quality and productivity has been thought to be inbreeding caused by the use of limited numbers of sorus-bearing individuals that are continuously used over generations to produce large numbers of offspring. One of the effective solutions is to use intraspecific hybrid vigor to produce new cultivars or to recreate the original agronomic features of the older cultivars. This study produced a sporophytic B013 (cultivar code) by crossing a pair of distantly related unialgal male and female gametophyte clones. The male was isolated from an individual collected from a farmed population at Rongcheng, China, while the female came from a Korean wild individual sporophyte. In comparison with four controls, the B013 sporophytic offspring demonstrated excellent blade quality (entirely dark green in the dried product), high alginate (29.7-32.9 %) and iodine (0.29-0.31 mg g(-1)) contents in the dried product, the lowest fresh weight/sun-dried weight (FW/DW) ratio and the smallest coefficients of variation for total length (7.4 %), width (6.9 %), and biomass output (14.6 %). In addition, this cultivar remained in a vegetative state from June to August, greatly reducing the biomass loss during the hot summer season. In comparison with seeding zoospores for seedling production, seeding a selected pair of unialgal gametophytes had apparent advantages in effectively preventing inbreeding depression, which gave rise to a uniformed product and provided new cultivars for large-scale farming.