Scientists Put Citrus in “Deep Freeze”
for Preservation
BY LAURIE GREENE, ASSOCIATE EDITOR
U.S. Department of Agriculture (USDA) scientists are creating a backup storage site or “genebank” for citrus germplasm in the form of small buds, called shoot tips, which have been cryopreserved, according to Jan Suszkiw, USDA Public Affairs Specialist.
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Plant physiologist Gayle Volk of the Agricultural Research Service (ARS) is applying the procedure to create a long-term genebank for important citrus varieties, breeding lines and wild citrus species. These efforts coincide with concern over the spread of citrus greening, an insect-borne disease first detected in the U.S. in August 2005, has been found in California, and which now threatens the nation’s citrus crop, valued at $3.4 billion in 2011-12.
In cryopreservation—that is, the process of being plunged into liquid nitrogen—Volk saw a way to safeguard valuable germplasm without fear of losing it to insects or disease, as well as natural disasters such as freezes, droughts and hurricanes. Instead of safeguarding whole plants or trees, her approach involves cutting tiny shoot tips from new growth, called “flush,” and cryopreserving the material for long-term cold storage inside state-of the-art vaults.
To date, Volk, together with ARS colleagues Richard Lee, Robert Krueger and others, have cryopreserved the shoot tips of 30 cultivars acquired from citrus germplasm collections managed at Riverside, Calif., by ARS in collaboration with the University of California-Riverside.
In preliminary experiments, an average of 53 percent of shoot tips survived being cryopreserved and thawed for use in rootstock grafting procedures, which enable generation of whole citrus plants.
