Re-domestication of sweet orange

The researchers sequenced a panel of 226 citrus accessions including sour oranges, landraces and cultivated citrus, and integrated published genomes of sweet orange, pummelo and mandarin in their analyses. Unlike sweet oranges, sour oranges exhibited high genetic and metabolic diversity and high variation in susceptibility to citrus canker. Shared heterozygous genomic segments between sour and sweet oranges traced their common parentage to mandarin and pummelo lineages. Phased telomere-to-telomere genomes of sweet and sour oranges were generated, and their two haplotype genomes show close relatedness to the mandarin and pummelo genomes, respectively. Integrative kinship analysis based on nuclear and chloroplast genomes of the citrus population enabled Liu et al. to deduce that sweet orange originated by hybridization between an ancient mother sour orange and a father Ponkan mandarin, and that sour orange probably originated from another more ancient cross between wild mandarin and pummelo.

To introduce genetic diversity, the researchers, according to their origin model, crossed a canker-resistant sour orange accession with a Ponkan mandarin line. Embryo rescue yielded 892 hybrids with diverse genetic and metabolomic compositions. Three hybrids displayed high genetic and phenotypic similarity to commercial sweet oranges. These artificial sweet oranges support this model of origin.