The Genetic Origins of Citrus

People all over the world eat citrus, whether it's lemons, oranges, limes, grapefruits or other species, but the genetic origins of cultivated citrus were unknown, until a team of researchers from China, found evidence of the origins of some of the most popular citrus species, cultivated today.

Actually, citrus species are among the most important fruit tress on the globe, and their history of cultivation is believed to go further than the past 4,000 years.

But researchers had a problem until now, because they had no idea about the exact origins of cultivated citrus like sweet orange (Citrus sinensis), lemon (C. limon), and grapefruit (C. paradisi), who had
remained a mystery.

Luckily for the team of Chinese researchers, led by Zhiqin Zhou from Southwest University, who analyzed amplified fragment length polymorphism (AFLP) fingerprints with chloroplast DNA (cpDNA) sequence analysis and nuclear internal transcribed spacer.

This is a technique that has been used successfully before, to assess the origin of potato cultivars.

The scientists said that “the combination of nuclear DNA and cpDNA data allowed us to identify the exact genetic origin of the cultivated citrus.”

The results were very conclusive; for example, bergamot and lemon are derived from citron and sour orange, and grapefruit is a hybrid that originated from a cross between pummelo and sweet orange.

The bergamot is a hybrid between citron and sour orange, with sour orange as the maternal parent and citron as the paternal parent.

Also, the sweet orange and the sour orange are hybrids of mandarin and pummelo, and the rough lemon is a cross between citron and mandarin.

The scientists noted that their “molecular evidence presented more convincing data than all other previous studies in supporting the origin of lime,” so it looks like the Mexican lime came from a species of Papeda – the female parent, and C. medica – the male parent.

A better understanding of the citrus genetic background is very important for the researchers, who said that they need to better characterize and use the citrus germplasm.

They added that future studies on the genetics and breeding of citrus will have a better starting point, thanks to this new research.

Their study was published in the Journal of the American Society of Horticultural Science.