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ISHS Acta Horticulturae 705: V International Walnut Symposium

APPLICATION OF MICROSATELLITE AND DOMINANT MOLECULAR MARKERS FOR THE DISCRIMINATION OF SPECIES AND INTERSPECIFIC HYBRIDS IN GENUS JUGLANS

Authors:   P. Pollegioni, A. Major, S. Bartoli, F. Ducci, R. Proietti, M.E. Malvolti
Keywords:   Juglans regia; Juglans nigra; hybridization; ISSR; RAPD; SSR; discrimination power
Abstract:
Persian walnut (Juglans regia) and Eastern black walnut (Juglans nigra) are economically important species for high quality timber and edible nut production. Juglans regia is an indigenous species of Eurasia from the Balkans to southwest China. Juglans nigra is native to the Eastern part of North America. Both species are widely spread in Europe. Our purpose was to characterize natural interspecific hybridization in chosen plots in Italy (Vicenza) by molecular markers: ISSR, RAPD and SSR. Thirteen ISSR primers, 17 RAPD primers and 10 primer pairs developed for J. nigra microsatellites amplified quality PCR products in both species and the hybrid plants. Both dominant (188 RAPD, 162 ISSR bands) and codominant markers (113 SSR alleles) reliably discriminated the individuals according to their nature and divided the total sample-set into three main clusters: 81 J. nigra, 49 J. regia and 8 interspecific hybrid genotypes. Comparison (Mantelís Tests) revealed a high statistical correlation for the sets of marker pairs (r ≥ 0.85). By one of the microsatellite primer pairs we detected two independent loci in J. regia, however, with substantial quantitative differences in amplification ability. ISSR analysis differentiated two sub-groups in J. regia samples and microsatellites revealed two sub-groups of J. nigra individuals. Performing microsatellite genotyping we identified a triploid tree with two genome-parts from J. nigra and one part from J. regia. The cytological analysis proved the triploid state showing a total number of 2n = 48 somatic chromosomes instead of the diploid set (32) in the premeiotic mitosis of the pollen mother cells. This study showed that both dominant and codominant markers are suitable tools for the identification of interspecific hybrids of walnut species. The highly variable microsatellite loci will be ideal for DNA fingerprinting, pedigree analysis and parentage testing for hybridogenic populations.
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