Researchers looked at the ancestral roots of modern day citrus fruits; the findings could help researchers find a cure for a deadly plant disease called citrus greening.

Researchers compared the genomes of sweet and sour oranges as well as mandarin and pummelo varieties, a University of Florida news release reported.

By understanding the cultivation history of these fruits researchers could gain how to genetic modifications and traditional breeding methods that could help protect them against the disease.

Most of the pummelo fruit was linked to the ancestor Citrus maxima. Easy-peel mandarin oranges were believed to be related to Citrus reticulate. Sweet oranges, which are most common, is a complex hybrid taking pieces from both lineages.

"Citrus has incestuous genes - nothing is pure," Gmitter, a UF Institute of Food and Agricultural Sciences faculty member, said in the news release. "Now that we understand the genetic structure of sweet orange, for example, we can imagine reproducing early citrus domestication using modern breeding techniques that could draw from a broader pool of natural variation and resistance."

New citrus trees are usually created through a process called grafting, which is a "method of propagation that binds the fruit bearing part of one tree to the root system of another," the news release reported. This allows for quick results but the method's uniform nature can spread susceptibility to disease.

Florida has a $9 billion crop industry that is currently being threatened by citrus greening. The disease is spread through a small bug called the Asian citrus psyllid, which sucks up leaf sap and leaves behind bacteria. The disease leaves fruit unsellable and can eventually kill the trees.

Researchers have suggested the entire industry could be wiped out within the next decade if action is not taken.

In the past researchers have tried to eliminate the psyllid and breed citrus rootstocks that show a greater resistance to the disease.