Genetic diversity of Ukrainian apple germplasm estimated with SSR markers

Apple (Malus domestica Borkh.) has a long tradition of cultivation in Ukraine. It can be grown in nearly the whole territory of Ukraine and in 2022 it occupied 7 0 % of the total fruit crop area. Traditionally substantial attention was paid to the choice of cultivars appropriate for commercial production. Already in the 1890s, the first large collection of apple cultivars was established in Mliiv by Levko Symyrenko, a well-known Ukrainian pomologist. Apple collections are now maintained in several research and/or breeding organizations: Institute of Horticulture of NAAS of Ukraine (Kyiv region), Podilska Research Station of Horticulture of IH (Vinnytsya region), and Research Station of Pomology named after L. Symyrenko of IH (Cherkasy region). These collections include ca. 2,500 accessions registered in the National Centre of Genetic Resources of Ukraine (NCGRU, Kharkiv), originating from Ukraine and other countries. Previously, morphological traits were used for the description and evaluation of apple cultivars in these collections. We hereby present the first results from a study using 16 SSR markers to characterize 167 apple accessions preserved within NCGRU, including traditional Ukrainian heirloom cultivars, cultivars and advanced selections of Ukrainian origin, and some important international cultivars. This has allowed an evaluation of the status of Ukrainian apple germplasm collections, revealing that a substantial proportion of cultivars was true to type. However, some cases of redundancies, erroneous labeling, synonyms, and homonyms were revealed. Several cultivars were found to be triploid. Evaluation of the extent and structure of genetic diversity available in Ukraine indicate that the germplasm is quite diverse with a limited population structure. These results will significantly contribute to an improved organization and coordination among Ukrainian collections as well as placing the Ukrainian apple germplasm into an international context.