Mature Citrus Transformation to Combat Diseases in Florida

Citrus canker and greening are causing severe economic losses in Florida by decreasing fruit quality, yield, and negatively affecting tree health. Traditional breeding programs for citrus are not very helpful in the fight against these diseases because the time for flowering and fruit production from seed of new cultivars can range from 3-20 years.  Mature tissue transformation technology enables genetic improvement and the early flowering and fruiting of scion.  The Agrobacterium transformation protocol was adapted to scion sweet orange cultivars 'Valencia', 'Hamlin', and 'Pineapple', and 'Ray Ruby' grapefruit, which are important to the Florida citrus industry.  Scion cultivars were transformed with Agrobacterium strain EHA 105 harboring binary vectors, pCambia 2301 or pTLAB21, containing the nptII selectable marker and GUS or GFP reporter genes, respectively. Transgenic plants were identified by PCR, NPTII immunostrip tests and GUS staining or GFP fluorescence. Southern blots are being performed to determine copy number of the transgenes in the independent events.  Some of the mature transgenics flowered 19 months after the transformation event was produced.  This technology will be useful in the genetic improvement of citrus.