Development, characterization, and cross-species/genera transferability of SSR markers for rubber tree (Hevea brasiliensis).

Genomic simple sequence repeat (SSR) markers are particularly valuable in studies of genetic diversity, evolution, genetic linkage map construction, quantitative trait loci tagging, and marker-assisted selection because of their multi-allelic nature, reproducibility, co-dominant inheritance, high abundance, and extensive genome coverage. The traditional methods of SSR marker development, such as genomic-SSR hybrid screening and microsatellite enrichment, have the disadvantages of high cost and complex operation. The selectively amplified microsatellite method is less costly and highly efficient as well as being simple and convenient. In this study, 252 sequences with SSRs were cloned from the rubber tree (Hevea brasiliensis) genome from which 258 SSR loci were obtained. The average repeat number was six. There were only 10 (3.9%) mononucleotide, trinucleotide, and pentanucleotide repeats, whereas the remaining 248 (96.1%) were dinucleotide repeats, including 128 (49.6%) GT/CA repeats, 118 (45.7%) GA/CT repeats, and 2 (0.8%) AT/TA repeats. A total of 126 primer pairs (see ESM) were successfully designed of which 36 primer pairs generated polymorphic products from 12 accessions of the cultivated species, 4 related species, and 3 species of the family Euphorbiaceae. In addition, investigations based on four genomic SSRs (GAR4, ACR22, CTR25, and GTR28) by cloning and sequencing provided evidence for cross-species/genera applicability, and homologous sequences were obtained from the rubber tree and Euphorbiaceae. Further analysis about the variation of the flanking regions of the four markers was carried out.

[Construction of genetic linkage map for rubber tree (Hevea brasiliensis) based on SSR markers.].

Out of 260 polymorphic loci screened from a total of 441 pairs of EST-SSR and genomic-SSR primers, 176 were used for constructing the genetic map of rubber tree (Hevea brasiliensis) by an F1 segregating population including 94 progenies from the cross Reyan 88-13xIAN873. Chi-square test carried out on the polymorphic loci used in constructing the map showed that 147 loci followed a segregation ratio of 1:1 and 12 loci followed a ratio of 1:2:1 and 17 loci followed a ratio of 1:1:1:1. Only 13 (7.38%) loci were distorted from the Mendelian ratio. The genetic linkage map consisted of 91 marker loci in 18 linkage groups and covered 1 937.06 cM with an average genetic distance of 21.29 cM between adjacent markers. The largest linkage group consisted of 16 marker loci, while the smallest one contained only 2 marker loci.