Analysis of the karyotype of the Russian apple tree clonal rootstocks bred at the Michurinsk State Agrarian University

For the first time, karyotypes of six forms of the clonal apple tree rootstocks bred at the Michurinsk State Agrarian University and their main cytogenetic features have been studied. In analyzing the mitotic division of root cells, it has been found that all studied genotypes in the (2n = 2x) diploid set have 34 chromosomes, which make 17 pairs of components. By the morphological structure, all the chromosomes are classified as metacentric and submetacentric; with that, no acrocentric and telocentrics chromosomes have been found. All chromosomes are small — 0.85 to 4.58 µm, their average length by genotypes varies from 2.05 ± 0.13 µm for the 2-15-2 hybrid to 2.71 ± 0.21 µm for the 2-9-83 form. This makes identification of homologous pairs of chromosomes difficult. Depending on the genotype, one to eight pairs of satellite chromosomes were found. Correlations of the relative indicators of chromosomes morphology among the studied clonal rootstocks were the following: by the index of their length Lr +0.85...+0.99; by the index of arm lengths -0.41...+0.35; and by the centromeric index -0.44...+0.31. By the obtained morphometric data of the metaphase plates, individual and generalized idiograms of the chromosomes of the clonal apple tree rootstocks have been built. The identified cytogenetic differences in the karyotypes of the studied forms of rootstocks are not essential, as evidenced by these genotypes' ability to interbreed with each other.