Citrus is a major worldwide crop. In 2017, the US Department of Agriculture’s Foreign Agricultural Service estimated production would exceed 50 million metric tons, with 10 percent of that contributed by the United States. To defend this crop against Huanglongbing (a.k.a., citrus greening), an infectious disease destroying whole orchards, researchers have begun employing genomics to better understand how citrus varieties respond to disease and other stresses. Through an early JGI Community Science Program project, JGI scientists played a leading role in the international consortium that sequenced and analyzed the Clementine mandarin and sweet orange.
Building on that early work, an international team led by researchers at the JGI, the Instituto Valenciano de Investigaciones Agrarias in Spain, and the Citrus Research and Education Center of the University of Florida, and including researchers from the French institutes INRAE and CIRAD have now proposed a revised genealogy of the major citrus cultivars and traced the origin of citrus back to the Himalayan foothills. This new scenario for the origin and diversification of citrus, derived from the analysis of additional genome data from a wide range of citrus types, was published February 7, 2018 in Nature. The work also offers new insights into the domestication of citrus.
According to the new study, citrus originated in an area limited by Eastern India, Northern Myanmar and Western Yunnan during the late Miocene. The first attempts at domesticating these fruits are thought to be by asexual propagation through apomictic seeds and the deliberate selection for specific traits; this process generated a complex network of relatedness among cultivated citrus that is recorded in the genomes. Southeast Asia has long been considered the birthplace of citrus, and the citrus plants are thought to have then migrated across Asia, reaching Australia circa 4-5 million years ago, during the early Pliocene period.
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- Wu GA et al. Genomics of the origin and evolution of Citrus. Nature. 2018 Feb 7. doi:10.1038/nature25447.
- INRA News Release: “A new look at the evolution of Citrus“
- BBC Science: “DNA story of when life first gave us lemons“
- JGI News Release: Retracing early cultivation steps: Lessons from comparing citrus genomes
- Sweet orange genome on Phytozome
- Clementine genome on Phytozome
- Fred Gmitter’s talk at the 2012 JGI Genomics of Energy & Environment Meeting: http://bit.ly/JGI7Gmitter