Development of high transferability cpSSR markers for individual identification and genetic investigation in Cupressaceae species.

Given the low substitution rate in plastomes, the polymorphic and codominant nature of chloroplast SSRs (cpSSRs) makes them ideal markers, complementing their nuclear counterpart. In Cupressaceae, cpSSRs are mostly paternally inherited, thus, they are useful in mating systems and pollen flow studies. Using e-PCR, 92 SSR loci were identified across six Cupressaceae plastomes, and primers were designed for 26 loci with potential interspecific transferability. The 26 developed cpSSRs were polymorphic in four genera, Platycladus, Sabina, Juniperus, and Cupressus and are suitable for Cupressaceae molecular genetic studies and utilization. We genotyped 192 Platycladus orientalis samples from a core breeding population using 10 of the developed cpSSRs and 10 nuclear SSRs, and these individuals were identified with high confidence. The developed cpSSRs can be used in (1) a marker-assisted breeding scheme, specifically when paternity identification is required, (2) population genetics investigations, and (3) biogeography of Cupressaceae and unraveling the genetic relationships between related species.

[Construction of genetic linkage maps of silver birch based on AFLP markers].

Based on the inheritance and segregation of amplified fragment length polymorphism (AFLP) markers, the first middensity linkage map for silver birch was constructed using a pseudotestcross mapping strategy. A segregating population including 80 progenies from the cross between Betula platyphylla Suk and B. pendula Roth was obtained. A set of 64 primer combinations were screened, and 34 pair primer combinations were selected to generate AFLP markers within a sample of 80 F1 progenies. A total of 451 segregating sites were identified. Among them, 362 belonged to 1:1 segregating site, and 41 belonged to 3:1 segregating site, 20 belonged to 1:3 segregating site, and others were found distorted from the Mondelian ratio. Altogether 362 sites segregating 1:1 (testcross configuration) were used to construct parent-specific linkage maps, 201 for B. platyphylla and 161 for B. pendula. One linkage maps resulted consisted of 201 marker sites in 14 groups with four or more sites per group, 10 triples and 14 pairs for B. platyphylla, which covered a map distance about 1 296.1 cM (Kosambi units), and the average map distance between adjacent markers was 15.5 cM. Another linkage maps resulted consisted of 161 marker site for B. pendula were mapped onto 17 groups with four or more sites per group, 8 triples and 4 pairs, which covered a map distance about 1 035.8 cM, and the average map distance between adjacent markers was 12 cM. Those maps can be used in QTL analysis and molecular assistant selection in birch breeding.

[Genetic linkage map of Betula pendula Roth and Betula platyphylla Suk based on random amplified polymorphisms DNA markers].

Based on the genetic inheritance and segregation of random amplified polymorphism DNA (RAPDs) markers, the first mid-density linkage map for silver birch was constructed by using a pseudo-testcross mapping strategy. A segregating population including 80 progenies from the cross between Betula pendula Roth and B. platyphylla Suk was obtained. A set of 1,200 random oligonucleotide primers were screened, and 208 primers were selected to generate RAPD markers within a sample of 80 F1 progenies. A total of 364 segregating sites were identified. Among them, 307 belonged to 1 : 1 segregating site, and 36 belonged to 3 : 1 segregating site, others were found distorted from the normal 1 : 1 ratio. Altogether 307 sites segregating 1 : 1 (testcross configuration) were used to construct parent-specific linkage maps, 145 for B. pendula and 162 for B. platyphylla. The resulting linkage maps consisted of 145 marker sites in 14 groups (four or more sites per group), 6 triples and 6 pairs for B. pendula, which covered the map distance about 955.6 cM (Kosambi units). The average map distance between adjacent markers was 14.9 cM, and 162 linked marker site for B. platyphylla were mapped onto 15 groups (four or more sites per group), 4 triples and 6 pairs, which covered the map distance about 1,545.8 cM, and the average map distance between adjacent markers was 15.2 cM. Further study is warranted to integrate the two maps to one density map and to locate important genes on the maps.