Citrus History Mystery Solved

Ernie NeffBreeding, Research

Citrus ryukyuensis

How modern citrus developed, particularly the popular mandarin variety, has long been a mystery to citrus breeders. A global partnership of scientists recently unraveled a big part of the mystery by analyzing the genome sequences of 69 East Asian traditional, wild and atypical citrus varieties. One of the researchers was Fred Gmitter, University of Florida Institute of Food and Agricultural Sciences horticulture professor at the Citrus Research and Education Center.

The researchers determined that the complexity of many varieties can be traced to three previously unrecognized ancestral lineages. They discovered a new wild citrus species native to the Ryukyu islands, a chain of Japanese islands stretching southwest from Kyushu to Taiwan. From one lineage, an important citrus trait arose — apomixis, or the ability of the tree to reproduce seedlings that are genetically identical to the mother tree. The spread of this trait throughout the broad citrus family was documented. All oranges, grapefruit, lemons and most citrus rootstocks possess this characteristic.

The researchers determined that apomixis was responsible in part for the creation and spread of new hybrid citrus species native to Japan in a rare evolutionary mechanism. The results provide insights into future breeding strategies that may produce more desirable and marketable commercial citrus.

“It is humbling to realize that the fruit we grow and eat today is the result of millions of years of both wild evolution and domestic cultivation,” Gmitter said. “Our findings raise more questions about what other citrus hybrids are out there and what characteristics may be beneficial to us as we look to breed more disease-resistant and environmental stress-resilient varieties. Understanding the past is really a window to the future.”

Other members of the international team were Guohong Albert Wu with the U.S. Department of Energy Joint Genome Institute at the University of California-Berkeley; Chikatoshi Sugimoto and Chika Azama, both with the Okinawa Institute of Science and Technology (OIST); Hideyasu Kinjo and Fumimasa Mitsube, both with the Okinawa Prefectural Government Agricultural Research Center; Manuel Talon with the Instituto Valenciano de Investigaciones Agrarias; and Daniel S. Rokhsar with OIST, the Joint Genome Institute and the Department of Molecular and Cell Biology at UC-Berkeley.

The research was published in Nature Communications.

Source: University of Florida Institute of Food and Agricultural Sciences

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