Microsatellite Loci Polymorphism of Apple (Malus domestica Borkh.) Genotypes with Different Ploidy Level

In this paper, the microsatellite (SSR) loci analysis was used to study apple genotypes with different levels of ploidy. A total of 47 samples were studied (9 diploids, 21 triploids, and 17 tetraploids) for seven microsatellite loci (GD147, Hi02C07, CH02c11, CH04c07, CH03d07, CH02c09, and GD12). It was possible to refine the pedigrees for some forms. It was established that the tetraploidss 20-9-30 and 20-9-27, selected in a hybrid family from the crossing of Wealthy 4x and Antonovka Obyknovennaya, were probably obtained from the self-pollination of the maternal form, since in the most loci they did not inherit alleles from the paternal form. As a result of the alleles distribution analysis, the spontaneous triploid cultivars Nizkorosloe and Sinap Orlovsky were revealed to be formed from the merge of an unreduced ovum and haploid pollen, since in the heterozygous loci both alleles are inherited from the maternal form and only one from the paternal form. According to the obtained data, studied tetraploids may be divided into two groups, which also reflect the features of tetraploids origin. The first group includes tetraploids inherited alleles from one initial diploid form (including spontaneous and induced tetraploids, as well as forms from self-pollination of the tetraploid maternal form). These teraploids, like diploids, amplify 1–2 alleles per locus (on average, for all 7 loci, one genotype amplifies 13 alleles). The second group includes tetraploids carrying alleles from several initial diploid forms. Tetraploids of this group are highly heterozygous and amplify 3–4 alleles at most loci (the maximum number of alleles at all loci, 24 alleles, was identified in the form 30-47-88). Tetraploids of the second group have a greater potential for the genetic diversity of its offspring. Analysis of polymorphism of microsatellite loci can be used (1) as an alternative or additional method for identifying the triploid hybrids from heteroploid crosses of orthoploid forms, which is based on the analysis of the loci most polymorphic in parental forms, and (2) for the analysis of true hybridity (verification of pedigrees), including tetraploid forms. Moreover, we identified the most polymorphic loci suitable for the above purposes. The aspects of qualitative and quantitative interpretation of the fragment analysis of microsatellite loci results are considered. The possibilities and limitations of the SSR analysis for detection of apple ploidy level are discussed.