In this crossing-experiment,the male parental strain (HR-6) ofPyropia haitanensis was characterized by faster growth speed in early growing stage,higher contents of photosynthetic pigments,but early maturity and shorter growth period in gametophytic blades phase,and low production of conchospores in conchocelis phase.The female parental strain (HR-5) of Pyropia haitanensis was characterized by lower growth speed in early growing stage,higher contents of photosynthetic pigments,later maturity and longer growth period in gametophytic blades phase,and high production of conchospores in conchocelis phase.From the F₁ color-sectored blades produced by the heterozygous conchocelies,an improved strain (WD-7) with better comprehensive properties than the parental strains was isolated.During the early growth period (30-45 days) of the blades,the absolute growth rate of the male and female parental strains was 6.68 and 3.63 cm/d,respectively,while that of WD-7 strain was 6.67 cm/d; During the middle growing stage (46-60 days) of the blades,the absolute growth rate of the male and female parental strains was 5.15 and 7.27 cm/d,respectively,while that of WD-7 strain was 11.54 cm/d.The male parental strain matured earlier,and most of the 35-day-old blades matured.While the WD-7 strain matured later which was similar to the female parental strain,a large number of blades matured after being cultured for 55 days.The mean thickness of the 35-day-old blades of WD-7strain was 29.87 μm,increasing by 10% and 16% in contrast with that of the male and the female parental strains,respectively.The total number of conchospores released from WD-7 strain was 183.42×10⁴,which was 1.17-fold and 0.57-fold of that of its male and female parental strains,respectively.The above results confirmed that WD-7 strain inherited the excellent characteristics of faster growing speed in early growing stage from the male parental strain,meanwhile inherited the excellent characteristic of late maturity,long growth period,faster growth speed in the middle growing stage and high production of conchospores from the female parental strain,and may offer an alternative for the Pyropia industry.