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Introduction: The self-incompatibility system in sweet cherry ( Prunus avium L.) prevents fertilization with own or genetically related pollen, and is genetically determined by the multi-allelic S -locus. Therefore, determining S -alleles is crucial for plant breeding and fruit production, as it enables the selection of compatible combinations of S -genotypes for successful pollination., Methods: In this study, S -alleles were identified in a total of 260 genotypes from the Caucasian region, the species' center of origin. S -allele genotyping was conducted using PCR fragment length analysis with the standard marker PaConsI-F/R2 and reference genotypes, complemented by sequence analysis through amplicon deep sequencing., Results and Discussion: The genotypes collected from Azerbaijan and Turkey exhibit a high allelic richness at the S -locus, particularly compared to modern sweet cherry cultivars worldwide. Nine previously undescribed S -alleles were identified and designated as S 45 , S 46 , S 47 , S 48 , S 49 , S 50 , S 51 , S 52 and S 53 . Given the expected high diversity for other traits, this plant material represents a valuable resource for further breeding research and introgression of new traits in future breeding programs. Furthermore, our results underscore that fragment length alone may not be sufficient for unambiguous assignment of S -alleles due to minimal length differences between different alleles. To address this issue, an S -allele reference ladder was developed using the rich diversity for precise assignment of the S -alleles. This tool can be applied in future experiments as a robust and cost-effective method for accurate S -genotyping across different runs and laboratories. Additionally, several selected S -genotypes were planted in a trial field and will be maintained as an S-allele reference collection., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Schröpfer, Schuster, Quero-Garcia, López-Ortega and Flachowsky.)

Release of bud dormancy in perennial woody plants is a temperature-dependent process and thus flowering in these species is heavily affected by climate change. The lack of cold winters in temperate growing regions often results in reduced flowering and low fruit yields. This is likely to decrease the availability of fruits and nuts of the Prunus spp. in the near future. In order to maintain high yields, it is crucial to gain detailed knowledge on the molecular mechanisms controlling the release of bud dormancy. Here, we studied these mechanisms using sweet cherry ( Prunus avium L.), a crop where the agrochemical hydrogen cyanamide (HC) is routinely used to compensate for the lack of cold winter temperatures and to induce flower opening. In this work, dormant flower buds were sprayed with hydrogen cyanamide followed by deep RNA sequencing, identifying three main expression patterns in response to HC. These transcript level results were validated by quantitative real time polymerase chain reaction and supported further by phytohormone profiling (ABA, SA, IAA, CK, ethylene, JA). Using these approaches, we identified the most up-regulated pathways: the cytokinin pathway, as well as the jasmonate and the hydrogen cyanide pathway. Our results strongly suggest an inductive effect of these metabolites in bud dormancy release and provide a stepping stone for the characterization of key genes in bud dormancy release.