INTERSPECIES HYBRIDIZATION OF PYRUS SPECIES ALONG THE SILK ROAD, DETECTED BY USING SPECIES-SPECIFIC S-ALLELES

Abstract

The interspecies hybridization within the Pyrus genus is compatible and natural hybrids in the interference regions of pear species could be detectable. Iran plateau has been one of these regions for thousands of years where natural hybridizations, germplasm entry along the Silk Road, and selection by human and natural factors caused significant diversity in this genus. Pear species have gametophytic self-incompatibility that is controlled by multi allelic S locus that seems to be species specific. The target of this research was determination of the S alleles of several pears including some considerable genotypes demonstrating special forms and characteristics. Detection of S alleles was achieved by DNA extraction, followed by PCR amplification of S locus using Sall-F/FB-R1 primers pairs and subsequent sequencing of these fragments. The S alleles in all cultivars were amplified and generally 5 different alleles were identified. Most interesting results were observed in ‘Khoj-57, ‘Konjuni’, Kaftar Bache’ and ‘Shirin Torkan’ genotypes that S allele of ‘Khoj-57 showed 99% similarity to S19 in Pyrus×bretschneideri, while the S allele in other cultivars had 95% similarity to S35 in P. ussuriensis. In the ‘Shekari' cultivar, two alleles were identified of which the smaller allele was similar to S7(Sh) in European pear and the larger allele was in 99% similarity to S19 in P.×bretschneideri. ‘Shahak’, ‘Shah Mive’ and ‘Khoj-1’ had a S7(Sh) allele, while S alleles of pears originated from upper latitudes of central Asia, including ‘Krus Siehan’ (S4) and ‘Krusalun’ (S8) contained normal P. communis S alleles. Neither of tested pears possessing S alleles of P.×bretschneideri and P. ussuriensis did not demonstrate morphological characteristics of these species, but exclusively have minor similarities such as round fruits and sandy texture of pulp. The results present the possible translocation and interspecies hybridization from East Asian species to the Iranian pear genotypes and in this process, The Silk Road may play a main role during past centuries.