Breeding and trial cultivation of Dongfang No. 3, a hybrid of Laminaria gametophyte clones with a more than intraspecific but less than interspecific relationship

Dongfang No. 3, a Laminaria hybrid, was bred by hybridizing a female gametophyte clone isolated from Line 7 of L. japonica with a male one isolated from Line LZZ which was developed through hybridizing female gametophyte clones of L. lonngissima and male gametophyte clones of L. japonica followed by continuous self-crossing and tolerances of strong irradiance and high seawater temperature targeted selection. The parental gametophyte clones of Dongfang No. 3 have a more than intraspecific but less than interspecific relationship. The seedlings of the hybrid were raised with the techniques of gametophyte clone asexual reproduction and hybridization and cultivated on trial. The dark brown hybrid has a wide, uniform, ripple-less and very tough blade and a very robust holdfast. A deep vertical groove and a half-round joint between stripe and blade distinguished also the hybrid from the varieties of L. japonica. The hybrid is tolerant of strong irradiance and high seawater temperature and resistant to the tissue rottenness of blade tip and edge. The hybrid matured later than the varieties of L. japonica widely used currently. The trial cultivation of this Laminaria hybrid has reached >406 ha in total. It increased the yield by 60.5% and 54.8% in average on that of Benniu (Control I) and Zaohoucheng (Control II), respectively, and by 62.4% and 75.8% on that of Line LZZ and Line 7, respectively, as were observed in Weihai, Shandong Province, China, in 3 continuous years, and by 57.0% and 32.1% in average on that of Control I and II, respectively, across 10 sites on the coast of north China in 2 continuous years. The breeding and application of Laminaria hybrids have paved an avenue of the direct use of heterosis, the easy integration of elite agronomical traits and fast renewing of Laminaria varieties.