Studies On The Genetic Diversity Among Plum Germplasm Resources And The Phylogenetic Relationships Of Main Plum Species

Three molecular markers such as RAPD, ISSR and SSR were employed to detect the genetic diversity in above 100 accessions of plum and its related species sampling from Chinese National Germplasm Repository for Plums and Tianshan Germplasm Repository for Wild Fruits, with the hope of assisting the management of plum germpalsm resources and elucidating the inter-species phylogenetic relationships. The accessions tested consisted of 7 plum species, including P. salicirta, P. ussuriensis, P. simonii, P. cerasifera, P. domestica, P. spinosa and P. nigra, 2 related species including P. armeniaca and P. tomentosa, wild European plums and natural / artifical hybrids between apricot and plum.A total number of 243 bands were generated using 47 RAPD primers for 108 accessions, with a average number of 5.17 per primer, among which 95.5% of the total bands was polymorphic and a total number of 103 bands using 12 ISSR primers for 104 accessions, with an average of 8.6, among which 96.1% was polymorphic. Totally, 654 alleles were found using 47 SSR primer pairs for 96 accessions, averaging 13.9 alleles per locus, and all of 47 loci were phylymorphic. The observed heterozygosity varied from 0.06 to 0.95 for 47 loci, with an average value of 0.47. The Jaccard's coefficients of similarity between accessions tested ranged from 0.11 to 0.98 for RAPD data, and from 0.19 to 1.00 for ISSR, from 0.042 to 0.98 for SSR. The efficiencies of three markers for identication of plum germplasm were SSR > RAPD > ISSR.Three markers involved in this study could be used for the purposes of discarding the duplicated collection, discriminating synonyms or homonyms, identificating the mislabelled accessions, analysing the relationships and detecting the diversity of plum accessions. Specially, RAPD and ISSR were suitable for utilization in germpalsm repositories or remote field breeding stations, as both were reliable, quick, uncomplicated and cheap methods if much care were exercised to control occasional contamination and the amplification conditions were identical for all reactions.The clustering and principle coordinate analysis showed that each of three markers could grouped the accessions surveyed into three main groups such as "apricot and hybrids of apricot and plum", Chinese-type plums" and "European plums". If the distinct (out of group) accessions were not considered, the higher diversity existed in Chinese plums than in European plums. The grouping results based three markers reflected the biogeographic distributions of main species but only the results based on SSR data was correlated with geographic origins of accessions.The results suggesting (1) the hybrids of apricot and plum were closer to apricot than to plum, (2) it was reasonable that 'Neili' was classed as a variant of P. salicina, (3) P simonii should be a variant of P. salicina, (4) P. ussuriensis was an independent species, (5) founder effect had possibly played an important role on the formation of P. simonii, (6) The introduced improved Chinese plum cultivars were clustered as same group with P. salicina despite most of which were hybrids of P. salicina and other diploidy species.European plums were closer to P. spinosa than to P. cerasifera and the result could not present direct evidence to support Crane & Lawrence assumption that European plum were originated from thehybrids of both species. Our results suggested that another possible evolutional way for P. domestica was that European plum derived from P. spinosa while the later containing two or more different genomes. A low level of diversity was revealed in wild European plums collected from Xinjiang of China, implying that this wild species was brought recently from Europe to Xinjiang and had be naturalized there rather than the ancestor of cultivated European plums.Chinese-type plum cultivars could be classed into three main groups such as "northeast China cultivars", "north China cultivars" and "south China and exotic cultivars". The improved Chinese-type plum cultivars introduced from Japan and US were closely related to...