Scientists Analyze Citrus Genomes to Produce Resistant Varieties

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.

Read more at http://www.nature.com/nbt/journal/vaop/ncurrent/full/nbt.2906.html and http://jgi.doe.gov/retracing-early-cultivation-steps-lessons-comparing-citrus-genomes/.