| Porphyra. yezoensis is the unique species in the western North Pacific, naturally distributing in the north of East Sea of Zhejiang Province of China, coast of Yellow Sea and Bo Sea, and the coast of the Korean Peninsula and Japan Islands. Porphyra is one of the cultivated seaweed of the most economic value in China. Traditional breeding technology is still the principle method. After 30 years of artificial breeding, a serious degradation of quality has happened in strains of P. yezoensis. As there is not any consummate standard available for the assurance and evaluation of the economic traits (e.g. thallus length, thallus width and thallus thickness and other quantitative traits) of Porphyra, suitable theory is absent in the breeding work, which makes a big disadvantage. The present work has determined the economic traits and evaluated the genetic parameters of the sporophyte (conchocelis) and gametophyte (thallus) of P. yezoensis by several aspects. The major results are as follows:1. Full range of the growth and economic traits of gametophyte of five strains of P. yezoensis and one strain of P. tenera have been recorded. The results show that:In the same culture conditions, varied strains of shell conchocelis have different maturity and the ability to release conchospores. Compared with wild strains, the cultivated strains of P. yezoensi incline to release in a short time range in higher temperature as a result of the designed selection and acclimatization for a long time. But P. tenera shows a different result. It is released in lower temperature than P. yezoensis. The conchospore of all strains need 1-2 days to accommodate. The difference in ratio of length to width is relevant with strains so that the ratio could be used as an important element in the assessment of germ plasm. The wet weight of unit area (WW), dry weight of unit area (DW) and ratio of WW to DW are all relevant with strains but the environment of sea area. The dry weight of unit area could be a reflection of the thickness of algae. The ratio of length-to-width, dry weight of unit area and ratio of WW to DW are negative correlated. Photosynthetic efficiency could be affected by strains and natural condition. Significant deviation does not exist in the amount of photosynthetic pigment among varied strains. The amount of photosynthetic pigment among varied strains is very stable.2. Half-sib like matings of sporophyte of P. yezoensis was built according to the life history and the characteristics of reproductive mode of P. yezoensis. The genetic parameter of the growth and the morphological traits of the half-sib family have been estimated by the analysis of variance. The results show that, generalize heritabilities of the growth rate, photosynthetic efficiency, the length and the width of cell of the half-sib family are 0.554,0.076,0.065 and 0.631. Of the total, the growth rate and the width of cell are traits of high hereditary capacity, while photosynthetic efficiency and the length of cell are traits of low hereditary capacity. The growth rate is a trait with high hereditary capacity and high coefficient of differentiation. It is a relevant better trait for the selection of good strain. Photosynthetic efficiency is a trait with low hereditary capacity and high coefficient of morphological differentiation. The length of cell is inverse correlated with the growth rate and photosynthetic efficiency, and the width of cell is positive correlated with the growth rate and inverse correlated with photosynthetic efficiency. Therefore, indirect breeding by other traits could be used when it is difficult to direct breed by some trait.3. P. yezoensis could produce monospore through asexual reproduction. It is an important part of the group of P. yezoensis. The present paper estimated some morphological genetic parameter of monospore offspring of P. yezoensis through the analysis of variance. The results show that, the monospore offspring of P. yezoensis could keep the merits from parents. The traits are arranged by hereditary capacity from high to low:the ratio of length-to-width (0.985),length of cell (0.979),width of cell (0.973),photosynthetic efficiency (0.694) and the growth rate (0.438). Among which, the ratio of length-to-width, photosynthetic efficiency, the length and width of cell are traits with high hereditary capacity. The ratio of length-to-width and growth rate is traits with great amplitude of variation and high aberration rate. Specified strains could be selected by these traits. The growth rate is the trait with the highest coefficient of environmental alteration. The growth rate of P.yezoensis is limited by environmental condition. Temperature is one of the main elements effecting the photosynthetic efficiency of gametophyte of P. yezoensis. In some range of temperature, the higher the temperature is, the higher the photosynthetic efficiency of gametophyte of P. yezoensis is; vice versa. Higher temperature might result in the smaller of body cell of gametophyte of P. yezoensis. But intensity of illumination does not show clear relationship with the volume of somatic cell.
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