Nowadays potato breeding is targeting to develop genetically divers high yielding varieties with multiple pathogen resistance traits. Interspecific hybridization jointed with marker-assistantselection (MAS) can effectively combine the R genes from different resistance sources. Additionally to effective pyramiding the target genes, MAS allows to restrict introgression of genetic factors conferring the undesirable traits, for example, male sterility of interspecific hybrids associated with Solanum stoloniferum-derived W/gamma cytoplasm that complicate the traditional breeding. Current study is targeting to search for the opportunities to improve the efficiency of introgressive hybridization between common potato and Mexican polyploid species Solanum. neoantipoviczii (=S. stoloniferum) and S. guerreroense using MAS with DNA markers for different cytoplasmic types and markers associated with major R-genes to the most harmful potato pathogens. DNA-based markers of genes for late blight resistance (R2 like, R3a, Rpi-blb1, Rpi-sto1), for extreme resistance to Potato virus Y (PVY) (Ryadg, Rysto, Ry-fsto) and for H1 gene for resistance to the root cyst nematode (Globodera rostochiensis, pathotype Ro1) were used in this study. Based on the MAS, hybrid genotypes with different combinations of these markers were selected. Among them, there were the clones with high field resistance to late blight and to PVY. Of 29 hybrid clones from different combinations of crossing with polyploid Mexican species used as the maternal forms, 15 had a W/ cytoplasmic type and were male sterile; both these traits were maternally inherited. The remaining hybrids with W/ cytoplasm produced fertile pollen and were used in interspecific crosses as pollinators. Selection of resistant clones with W/alpha cytoplasm and elimination of genotypes with sterile W/ cytoplasm among wild species germplasm could increase the probability of obtaining male fertile introgressive lines. This approach allows to obtain the multi-species hybrid genotypes that combine R genes for resistance to pathogens from different Mexican species and to avoid various types of male sterility in breeding. The joint use of two systems of DNA markers, i.e. nuclear markers associated to R genes, and cytoplasmic markers for male sterility factors, could reduce costs and increase efficiency of target gene pyramiding programs.

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A b s t r a c tA modified method of combined chemo-thermotherapy for eradication the most damaging viruses in potato plants is proposed. The materials for study included 91 clones of 85 accessions of three South-American cultivated species Solanum phureja (18 accessions), S. stenotomum (26 accessions), S. tuberosum (S. tuberosum ssp. andigenum and S. tuberosum ssp. tuberosum) (41 accessions) from the VIR field collection (N.I. Vavilov All-Russian Institute of Plant Genetic Resources). The results of ELISA for 91 clones from the field collection and RT-PCR analysis of the corresponding microplants, when introducing clones into in vitro culture, have shown that all material was infected by viruses (potato viruses Y, X, S, M and potato leafroll virus -PVY, PVX, PVS, PVM and PLRV) to varying degrees. Single infections were detected in 25.3 % of the 91 clones, and the remaining clones were multi-infected and contained several viruses in various combinations. Based on the termo-and chemotherapy protocols as well as complex therapy used in leading potato genebanks (Leibniz Institute of Plant Genetics and Crop Plant Research -IPK, Germany; International Potato Centre -CIP, Peru), we have developed a modified method of combined therapy comprising three successive cycles of in vitro plant cultivation on Murashige and Skoog basal medium (MS) supplemented with ribavirin (30 mg/l) at 37 С during 4 weeks. Between the cycles, the microplants were incubated for 2 days at 26 С on the same medium with ribavirin. Each clone was tested for the presence of viruses by RT (revers transcription) PCR before and after the combined thermo-chemotherapy. In RT-PCR, 42 clones (46 %) were completely free from tested viruses, 44 % were free from some viruses, and 10 % of the clones were unable to improve. On the whole of 91 clones, PLRV was eliminated from 72.7 %, PVY from 71.4 %, PVM from 63.9 % and PVS from 57.4 % of microplants. Differences in elimination frequency between the viruses were not significant (р > 0.05). Also, there were no significant differences in elimination of different viruses between the accessions of different cultivated species. The difference of this modification from IPK protocols (Germany) lays in simultaneous effect of high temperature (37 C) and ribavirin (instead of sequential application), and, unlike the CIP (Peru) scheme, it comprises less steps.

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