A Novel Set of EST-Derived SSR Markers for Pear and Cross-Species Transferability in Rosaceae

Pear is a fruit species with worldwide distribution belonging to the Rosaceae family. In this study, transcriptomes of 12 different tissues of pear were newly assembled, with a total of 17,353 SSR loci identified. Within these, repetitive sequences with dinucleotide and trinucleotide motifs were more abundant than other types. We developed 194 EST-SSR makers from the assembled sequences to test on seven pear varieties from different genetic backgrounds, on which 132 EST-SSR primers had amplicons. There were 108 primers with dinucleotide and trinucleotide motifs detecting a total of 311 alleles, with an average per primer of 2.88 and 2.86, respectively. These had better quality than primers with tetranucleotides, pentanucleotides, and hexanucleotides. Fifty polymorphic markers divided 36 pear genotypes into two groups with a similarity coefficient of 0.62. Results showed that Japanese pears had a comparatively close relationship with Chinese pears, indicating the great potential of the novel EST-SSR makers in future evaluations of pear germplasm. Furthermore, 54 EST-SSR markers were selected to test transferability to 96 other Rosaceae cultivars from eight species, including Japanese apricot, plum, apricot, peach, cherry, apple, strawberry, and loquat. Seventeen EST-SSR primers had PCR amplification products in at least one of the 96 accessions, with the highest transferability was from pear to apple at 29.63 %. Transferability from pear to Japanese apricot, plum, apricot, peach, cherry, strawberry, and loquat was 9.26, 14.81, 11.11, 12.96, 5.56, 3.7, and 12.96 %, respectively. Therefore, the newly developed EST-SSR markers can contribute to exploring the genetic relationship, evolution and comparative genomics, and gene introgressions in the Rosaceae family.