The Selection Of Crosses With Heterosis For Gracilaria Lemaneiformis And AFLP Analyses

Gracilaria lemaneiformis is one of the important agarophytic species of Gracilaria , and the cultivation of G. lemaneiformis has ranked the third place of algal mariculture following Laminaria and Porphyra in China, which greatly promoted the industry of agar production and exportation of China. Besides, G. lemaneiformis is also an ideal material for studies of genetics and molecular biology. The aim of this study is to conduct the selection of crosses with heterosis developed through sexual crossing between G. lemaneiformis from different locations, and the analyses of relative quantitative traits and AFLP, so as to investigate the heterosis mechanism of G. lemaneiformis and to provide practical data for its genetic breeding.In this study, three wild type tetrasporophytes of G. lemaneiformis from Qingdao(QD), Shidao (SD) and Longxudao (LXD) of China were used as parents, and their male and female gametophytes were obtained by laboratory incubation. A material system including parent tetrasporophytes, parent gametophytes, self-fertilization tetrasporophytes, hybrid tetrasporophytes and hybrid gametophytes was constructed. Comparison of relative economic traits indicates that, both tip elongation rate and biomass increase rate of hybrid F1 tetrasporophyte (F1sq), which is generated by Shidao female gametophyte and Qingdao male gametophyte, is 60% higher than the average value of its corresponding parent tetrasporophytes. While, no significant differences on contents ofα- galactosidase and photosynthetic pigment were detected. Besides, the comparison result between crosses and reciprocal crosses shows that cytoplast genetic contribution may not be involved in tip elongation rate of G. lemaneiformis.The AFLP analysis system for G. lemaneiformis was established, and the key steps were optimized. EcoRⅠ-TaqⅠrestriction enzymes combination was selected for digestion reaction through comparison. Then the optimized reaction system was applied to investigate the genetic background of QD and 981. A total of 1794 loci were detected by 64 pairs of EcoRⅠ/TaqⅠprimer combinations, and 69 polymorphic AFLP markers were revealed, the ratio of polymorphic marker was only 3.8%. AFLP analysis showed that G. lemaneiformis from Qingdao and its selected strain 981 displayed the highest genetic similarity, on the other hand, 981 differs greatly from QD in high growth rate, high temperature tolerance, and the yield and quality of agar, the different loci of AFLP might include genetic information relative to these fine traits.Quantitative traits of growth rate and photosynthetic pigment content as well as amplified fragment length polymorphism (AFLP) were detected for investigating the genetic diversity of six strains of Gracilaria lemaneiformis, three of which were collected in Qingdao (QD), Shidao (SD) and Longxudao (LXD) of China, the forth named 981 is high-temperature selected strain from QD , the other two strains came from South Africa (Sa) and Venezuela (Lv) respectively, and Gracilaria tenuistipitata var. liui (Ten) was used as outgroup control. The results of quantitative traits examination showed that obvious difference of growth rate and pigment content occurred in G. lemaneiformis from different locations. The largest value of tip elongation rate and biomass increase rate is 2.56 and 5.46 times of the smallest value respectively. Among three phycobiliproteins, Allo-phycocyanin (APC) is relatively conservative, phycoerithrin (PE) is more flexible, and phycocyanin(PC) is in the middle. In AFLP analysis, a total of 762 loci were obtained by 16 pairs of EcoRⅠ/TaqⅠprimer combinations, and the ratio of polymorphic marker was 91.3%. The genetic distance between pairs of genotypes ranged from 0.0422 (981 and QD) to 0.8881(981 and Lv). Cluster tree obtained with UPGMA analysis demonstrates that all the materials involved were divided into 2 groups. One group includes 4 strains G. lemaneiformis from China and Sa, the other consists of Lv and Ten. In addition, both quantitative traits examination and AFLP analysis indicate that Lv should not to be divided into the species of G. lemaneiformis.