A self-compatible pear mutant derived from γ-irradiated pollen carries an 11-Mb duplication in chromosome 17

Self-compatibility is a highly desirable trait for pear breeding programs. Our breeding program previously developed a novel self-compatible pollen-part Japanese pear mutant (Pyrus pyrifolia Nakai), '415-1', by using γ-irradiated pollen. '415-1' carries the S-genotype S, with "d" indicating a duplication of S ₅ responsible for breakdown of self-incompatibility. Until now, the size and inheritance of the duplicated segment was undetermined, and a reliable detection method was lacking. Here, we examined genome duplications and their inheritance in 140 F₁ seedlings resulting from a cross between '515-20' (S) and '415-1'. Amplicon sequencing of S-RNase and SFBB18 clearly detected S-haplotype duplications in the seedlings. Intriguingly, 30 partially triploid seedlings including genotypes S, S, S, S, and S were detected among the 140 seedlings. Depth-of-coverage analysis using ddRAD-seq showed that the duplications in those individuals were limited to chromosome 17. Further analysis through resequencing confirmed an 11-Mb chromosome duplication spanning the middle to the end of chromosome 17. The duplicated segment remained consistent in size across generations. The presence of an S seedling provided evidence for recombination between the duplicated S segment and the original Shaplotype, suggesting that the duplicated segment can pair with other parts of chromosome 17. This research provides valuable insights for improving pear breeding programs using partially triploid individuals.