Development of a doubled haploid mapping population of Pyropia yezoensis and measurement of the economic characters of blade v1
Authors: Huang Linbin , Yan Xinghong 
Published: February 2019

Pyropia yezoensis is one of the most valuable and widely cultivated seaweeds across the world, however, there is limited data regarding its genetic background underlying complex economic traits, especially information on quantitative trait loci. The lack of mapping population was the most probable cause, because it was the basic of linkage analysis. In the present study, a red-type and fast-growing pigmentation mutant Py-HT and a wild-type strain Py-LS who had sufficient variation for traits of interest at both DNA and phenotypic level were crossed under control. The heterozygote (heterozygous conchocelis) was identified among conchocelis colonies which were developed from single zygotospore released from zygotosporangia of fertilized Py-HT blade, based on the result that 91.9% F1 gametophytic blades developed from the conchospores of heterozygous conchocelis were linearly sectored with 2-4 color sectors of parental colors. Afterwards, 57 chimeric blades with four color sectors were screened from thousands of F1 blades and 228 color sectors were separated according the boundaries of color sectors for single culture. A single zygotospore released from zygotosporangia of one sector through selfing was selected and then developed into homozygous conchocelis, which was declared a double haploid strain. Finally, a mapping population with 152 strains obtained from 38 of the 57 four color sectored blades was developed, which will contribute for the construction of genetic linkage maps and analysis of quantitative trait loci of P. yezoensis blades. Further stud found that all 6 traits (L50, W50, FW50, SGR-L, SGR-W and SGRFW) were quantitative traits when analyzed by one-sample Kolmogorov-Smirnov test. The means of 4 traits of DH population lines were between their parents, among which W50 was nearer to female parent, and FW50, SGR-L and SGR-FW were nearer to male parent. L50 and SGR-W showed transgressive inheritance, among which L50 was lower than low value parent (female), and SGR-W was higher than high value parent (female). Coefficient of variation of the 6 traits of DH population was between 21.11%–56.68%, which meant that they had intermediate variability. Highly significantly positive correlations were observed between L50 and W50, L50 and FW50, W50 and FW50, and between SGR-L and SGR-W, SGR-L and SGR-FW, SGR-W and SGR-FW. Heritability of L50, W50 and FW50 were 58.17%, 64.00% and 57.64%, respectively; and the number of genes controlling the 3 traits was 6.61, 12.63 and 8.09, respectively. The equation of the curve between heritability (y) and the number of genes (x) was y=0.2922x2–4.6533x+76.162 (R2=1). According to estimated coefficients of skewness and kurtosis of the 3 traits tested, gene interactions were found to be absent for L50 and FW50, respectively, and complementary interactions were observed in W50 and SGR-W respectively, and duplicate interactions were observed in SGR-L and SGR-FW respectively. The results indicated that L50 and FW50 could be selected at early generation by their high heritabilities, less controlling genes and no gene interactions, and indirect selection could be applied between L50, W50 and FW50 to improve breeding efficiency of P. yezoensis because of their high correlations between each other.