Diverse varieties of citrus came from two wild citrus species that diverged
in Southeast Asia 5 million years ago, according to a new research published
in the June 2014 issue of Nature Biotechnology. The study was conducted by
an international group of scientists from the United States, France, Italy,
Spain, and Brazil. The researchers analyzed and compared the genome
sequences of 10 diverse citrus varieties, including sweet and sour orange
along with several important mandarin and pummelo cultivars with a common
objective of finding out how citrus varieties have evolved and how they
react to biotic and abiotic stresses.

Genomic analyses revealed that pummelos represent a single citrus species
(Citrus maxima), but that is not the case in cultivated madarins which are
introgressions of C. maxima into the ancestral mandarin species Citrus
reticulata. Sweet orange, the most cultivated citrus variety, is actually an
offspring of previously admixed individuals, but sour orange is a hybrid of
pure C. maxima and C. reticulata, thus implying that wild mandarins were
part of the early breeding germplasm.

"Now that we understand the genetic structure of sweet orange, for example,
we can imagine reproducing the unknown early stages of citrus domestication
using modern breeding techniques that could draw from a broader pool of
natural variation and resistance," said study leader Fred Gmitter of the
University of Florida Citrus Research and Education Center.

[www.nature.com]