Large-Scale Screening and Identification of S-RNase Alleles in Chinese and European Apricot Accessions Reveal Their Diversity and Geographic Distribution Patterns

Apricot (Prunus armeniaca L.) exhibits a gametophytic self-incompatibility (GSI) system. To identify the S-genotypes of the main apricot cultivars, including 133 native Chinese cultivars and 35 foreign accessions, PCR was performed using a combination of five primers based on the conserved regions of Prunus S-RNase genes. After cloning and sequencing the PCR products, the S-genotypes of all 168 apricot cultivars were determined. A total of 46 different S-RNase alleles, with 15 new alleles, were identified. For all 168 accessions, the top five most frequent S-alleles were S8, S11, S9, S16, and S53. S11, S8, and S16 were the most frequent in Chinese cultivars, and S9, S8, and S2 were mostly found in European accessions. For Chinese apricot cultivars, the distribution of S-alleles among five geographic regions was also investigated. In Northwest China, S16 was the most frequent S-allele. In the Xinjiang region, S66, S49, and S14 were the top three most frequent S-alleles. In North China, S8, S11, and S53 were the top three most frequent S-alleles. In addition, the self-compatible type, SC, was not detected in these 133 Chinese accessions. Finally, the phylogenetic tree of apricot S-alleles indicated that there are four groups of S-RNase genes (S97/S106, S14/S14a/S66, S9/S17/S44, and S23/S53) presenting a very close relation. These results provide more data on the S-genotypes of apricot accessions, which can support future breeding programs by aiding in the selection of the appropriate parents and contributing to efficient orchard design by combining cultivars with suitable pollinizers.