Disease-resistant sweet oranges

Long-term selective breeding of crops can result in reduced genetic diversity and high sensitivity to pathogenic diseases. The de novo domestication of the wild relatives of such crops can facilitate the identification and breeding of disease-resistant variants, but this requires knowledge of the evolutionary origins of crop cultivars and specific metabolites or genomic regions that confer disease resistance. Writing in Nature Genetics, Liu and colleagues take on this challenge in sweet orange — an important fruit crop that is sensitive to a bacterial disease known as citrus canker. They assessed the nuclear and chloroplast genomes of 305 citrus accessions (plant materials from a single species collected at one time from a specific location) from southern China, including accessions of sweet orange, sour orange, pummelo and mandarin. Having inferred that sweet orange originated from hybridization between a sour orange accession (probably the maternal parent) and a mandarin, they confirmed it with artificial hybridization experiments between a canker-resistant sour orange and a mandarin. Using comparative metabolomic analysis and experiments with antibacterial agents, they also identified plant metabolites with broad antibacterial activity that confer resistance to citrus canker. Of 215 hybrids generated in the experiment, 3 had remarkable phenotypic similarity to commercial sweet oranges. One also accumulated higher levels of defense-related metabolites than its canker-resistant sour orange progenitor and was resistant to citrus canker when inoculated with the causative bacterium. These findings offer a feasible route to using sour oranges for the de novo domestication of disease-resistant sweet oranges.

Original reference: Nat. Genet. 57, 754–762 (2025)