Genebank collections preserve many old cultivars with ancient breeding history. However, often, cultivars with synonymous or incorrect names are maintained in multiple collections. Therefore, pomological and genetic characterization is an essential prerequisite for confirming trueness-to-type of cultivars in gene bank collections. In our study, 1442 single sweet cherry (Prunus avium L.) trees of the German Fruit Genebank were evaluated according to their trueness-to-type. For this purpose, pomological analysis was performed, in which the accessions were assigned totheir historical cultivar names. The pomological identifications were based on several historical reference sources, such as fruit references from historical cherry cultivar and fruit-stone collections, as well as historical pomological literature sources. In addition, the cherry trees were genetically analyzed for cultivar identity using 16 SSR markers. Based on pomological characterization and genetic analysis for the majority of the trees (86%), cultivar authenticity could be confirmed. Most markers were highly discriminating and powerful for cultivar identification. The cherry collection showed a high degree of genetic diversity, with an expected heterozygosity He = 0.67. Generally, high genetic admixture between cultivars of different geographic origin and year of origin was obtained after STRUCTURE analysis, demonstrating the extensive exchange of genetic information between cherry cultivars in the collection over time. However, the phylogenetic tree calculated by DARwin reflected the geographic origin of selected cherry cultivars. After parentage analysis with CERVUS, paternity could not be confirmed for three cultivars, indicating the necessity of further pedigree analysis for these cultivars. The results of our study underlined the general importance of evaluating the authenticity of cultivars in genebank collections based on genetic and pomological characterization.

ISHS IV International Cherry Symposium SOUR CHERRY BREEDING AT DRESDEN-PILLNITZ

Sour cherry ( Prunus cerasus L.) is an economically important allotetraploid cherry species believed to have evolved in the Caspian Sea and Black Sea regions. How, when and where exactly the evolution of this species took place is unclear. It resulted from a hybridization of the tetraploid ground cherry ( Prunus fruticosa Pall.) and an unreduced (2n) pollen of the diploid ancestor sweet cherry ( P. avium L.). Some indications implement that the genome of sour cherry is segmental allopolyploid, but how it is structured and to what extent is unknown. To get an insight, the genome of the sour cherry cultivar ‘Schattenmorelle’ was sequenced at ~400x using Illumina NovaSeq ^TM short-read and Oxford Nanopore long-read technologies (ONT R9.4.1 PromethION). Additionally, the transcriptome of ‘Schattenmorelle’ was sequenced using PacBio Sequel II SMRT cell sequencing at ~300x. The final assembly resulted in a ~629 Mbp long pseudomolecule reference genome, which could be separated into two subgenomes each split into eight chromosomes. Subgenome Pce _S _a which originates from P. avium has a length of 269 Mbp, whereas subgenome Pce _S _f which originates from P. fruticosa has a length of 299.5 Mbp. The length of unassembled contigs was 60 Mbp. The genome of the sour cherry shows a size-reduction compared to the genomes of its ancestral species. It also shows traces of homoeologous sequence exchanges throughout the genome. Comparative positional sequence and protein analyses provided evidence that the genome of sour cherry is segmental allotetraploid and that it has evolved in a very recent event in the past.

ISHS III Balkan Symposium on Fruit Growing New cultivars of first quality cherries at Dresden-Pillnitz

Sour cherry (Prunus cerasus L.) is an economically significant species in the Rosaceae family. Hitherto, there had been limited genetic and genomic resources to elucidate important horticultural traits in this species mainly because of the complex polyploid nature of its genome, a hybrid between Prunus avium and Prunus fruticosa. An important trait that has not been well studied in sour cherry is resistance to cherry leaf spot (CLS), caused by the fungus Blumeriella jaapii. This work took advantage of the RosBREED 6 + 9 K SNP array to study the genetic basis of CLS resistance and inheritance in sour cherry. We established an F1 segregating population by crossing two cultivars, ‘Schattenmorelle’ and ‘Pc 2’ and genotyped both parents and the progeny with the cherry 6 + 9 K SNP array and SSR markers. We evaluated both parents and progeny for resistance and susceptibility to CLS under field conditions. The applied marker systems facilitated the development of parental genetic maps, and the identification of two stable QTLs associated with CLS resistance, CLSR_1f in ‘Pc 2’ and susceptibility, CLSS_1f, in ‘Schattenmorelle’ explaining 40.9% and 21.5%, respectively, of the phenotypic variation within the population. The mechanism of resistance in sour cherry appears to be independent of the CLS resistance QTL, CLSR_G4, previously identified in P. canescens, as the CLSR_G4-QTL and associated allele were not identified. Based on our findings, we propose a two-gene model for CLS resistance in sour cherry involving a susceptibility QTL, which might explain why some CLSR_G4-resistant plants in previous studies were susceptible.