Breeding work in the Michurinsk State Agrarian University (MSAU) is based on one of the eff ective strategies for producing high-quality planting material for establishment of intensive perennial fruit plantations – the use of apple varieties and clone stocks that are highly resistant to extreme factors and immune to diseases. As a result of many years of breeding work, the MSAU is the originator of 24 forms of clonal stocks (out of 46 forms allowed for cultivation in the Russian Federation) and the patent holder of 8 stocks. In 2018, 4 apple clonal rootstocks (70-20-20, 70-20-21, 71-7-22, 75- 1-62) were included in the State Register of Breeding Achievements admitted to cultivation on the territory of the Russian Federation. The main requirements for apple stocks for intensive orchards are high resistance to major environmental factors; suitability for intensive types of orchards; increased resistance to pathogens; good ability to vegetative propagation; lack of root shoots in the orchard; increase of productivity, early fruited varieties, quality of fruits. The advantages of planting material of apple trees on weak clonal rootstocks of the MSAU breeding are established: high compatibility of rootstocks with the best zoned and promising apple varieties; high frost resistance and winter hardiness of the root system, withstanding up to -16 °С – there are no foreign analogues on this basis; high resistance of stocks to the bacterial burn (unlike most foreign stocks); accelerated entry into fruiting, the onset of the period of commodity bearing fruit in the orchard on the 3rd ... 5th year; high productivity of commercial apple plantings in the conditions of Central Russia – an average of 25 to 40-50 tons / ha. For widespread introduction into production, the most studied clonal stocks of the MSAU breeding are recommended in Russia and in many countries of the world: the Paradizka Budagovsky (dwarf), 62-396 (half-dwarf), 54-118 (medium-sized). To increase the productivity and the resistance of plants and the eff ectiveness of Russian horticulture as a whole, it is necessary to create mother nurseries of apple rootstocks, free from harmful viral infections (repositories).

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For use in breeding work, the methods of complex accelerated cytological diagnosis of genotypes of fruit and berry crops with an altered ploidy level were optimized. The proposed diagnostic method was tested on polyploids of the genus Malus, Fragaria, Ribes, Rubus, rowan-pear hybrids and is recommended for wide scientific and practical application in the plant breeding and cytology. The effectiveness of this method is ensured by its availability and reliable statistical differences in accounting parameters. In a comprehensive cytological diagnosis of forms of fruit and berry crops with an increased level of ploidy, it is proposed to first study the morphoanatomical traits (sizes and proportions of stomatal guard cells, the number of chloroplasts in them, the diameter of pollen grains). This will significantly reduce the time of laboratory analysis and field assessment by deleting forms with unchanged indicator values.

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The complex morphometrical traits of leaf epidermal tissue in species forms Pyrus communis L. and Malus baccata Borkh. were studies to establish statistically significant differences. These traits can serve as a marker selective indicator of saturation degree estimation in a complex of genes from each parental species, combined in hybrid progeny genotypes by distant hybridization. The stomatal density in leaf epidermal tissue has the most variability among studied morphometric traits of apple and pear wild forms and their hybrids. A mode, kurtosis and skewness of numerical data series are most appropriate to use for a comprehensive statistical analysis of variation curves, obtained from study of different genotypes by the quantitative traits of stomatal guard cells. The differentiation of genotypes into groups, graphically shown in a shape of polymodal variation curves, was noticed among the population of F2 hybrids. The progeny from free pollination of F1 hybrids has the largest values of stomatal morphological traits such as the widest data series, the coefficient of variation and the variance. A tendency of partial deviation in stomatal quantitative traits and stomatal index in the studied F2 hybrids between apple and pear in the direction of a female parent was revealed.