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In the long history of human relations with flowering cherry trees in Japan, 'Somei-Yoshino' occupies an exceptional position among a variety of flowering trees: it is a self-incompatible interspecific hybrid but has been enthusiastically planted by grafting throughout Japan, due most likely to its flamboyant appearance upon full bloom. Thus, 'Somei-Yoshino' gives us a rare opportunity to trace and investigate the occurrence and distribution of somatic mutations within a single plant species through analysis of the genomes of the clonally propagated trees grown under a variety of geographical and artificial environments. In the studies presented here, a total of 46 samples of 'Somei-Yoshino' trees were collected and their genomes were analysed. We identified 684 single nucleotide mutations, of which 71 were present in more than two samples. Clustering analysis of the mutations indicated that the 46 samples were classified into eight groups, four of which included 36 of the 46 samples analysed. Interestingly, all the four tree samples collected in Ueno Park of Tokyo were members of the four groups mentioned above. Based on comparative analysis of their mutations, one of the four trees growing in Ueno Park was concluded to be the closest to the original ancestor. We propose that somatic mutations may be used as tracers to establish the ancestral relationship amongst clonally propagated individuals. [ABSTRACT FROM AUTHOR]

Hybridizations involving different species are often hindered because of incompatibility reactions. Although these reproductive barriers have been observed in many plant species, the underlying mechanisms remain to be comprehensively elucidated. In this study, we detected a hybridization barrier between apple (Malus × domestica) and pear (Pyrus spp.) belonging to different genera in the subtribe Malinae of the family Rosaceae. Pollination experiments revealed that Pyrus pyrifolia (Japanese pear) pollen is compatible with Malus pistils, whereas Pyrus communis (European pear) pollen is not. These results imply there is a distinct cross-(in)compatibility reaction occurring in Pyrus species. Based on the varying pollen tube behaviors among Pyrus species, genetic analysis was conducted to identify the genomic region responsible for the intergeneric barrier. Malus–Pyrus intergeneric hybrids were used to detect distorted segregation regions by combining genome sequencing and fine-scale genotyping data. We defined a single locus on chromosome 5, in which P. pyrifolia-derived alleles were exclusively inherited to the intergeneric hybrids from the Pyrus interspecific hybrid. Of the 235 genes in this genomic region, 80 exhibited a specific pollen-expression pattern, including genes involved in self-incompatibility reactions. These candidate genes are herein discussed regarding their possible functions related to reproductive isolation. [ABSTRACT FROM AUTHOR]