Genetic Diversity of Apple Clonal Rootstocks from the Collection of the Michurinsk State Agrarian University Based on SSR Markers.

The Michurinsk State Agrarian University (Michurinsk SAU) is one of the leading centers for breeding apple clonal rootstocks. A diverse collection of apple rootstocks, founded in 1930s by V.I. Budagovsky, is maintained at the Michurinsk SAU. In the present study, 87 rootstocks from this collection were analyzed using 18 SSR markers to assess their genetic diversity and relatedness. The detected polymorphism level was rather high compared to the previous estimates of apple rootstock genetic variability. A total of 199 alleles were detected with an average of 11.1 alleles per locus. Among the detected alleles, 67 (33.67%) were rare and 43 (21.61%) were unique. The average PIC value was 0.73, and the expected and observed heterozygosity averaged 0.76 and 0.69, respectively. All the studied accessions except two could be identified with the used marker set. Cluster analysis revealed several groups according to the rootstocks' pedigrees and genetic origin. Furthermore, Structure analysis revealed two main groups of the studied rootstock accessions. No significant differentiation of the studied sample according to dwarfing ability was detected, while weak differentiation was detected according to leaf color. SSR genotyping data can be used for rootstock fingerprinting and pedigree verification and will facilitate collection management. In addition, data on the genetic diversity and structure of the studied collection may be useful for further development of the Michurinsk SAU rootstock breeding program.