A dark incubation period is important for Agrobacterium-mediated transformation of mature internode explants of sweet orange, grapefruit, citron, and a citrange rootstock.
BACKGROUND
Citrus has an extended juvenile phase and trees can take 2-20 years to transition to the adult reproductive phase and produce fruit. For citrus variety development this substantially prolongs the time before adult traits, such as fruit yield and quality, can be evaluated. Methods to transform tissue from mature citrus trees would shorten the evaluation period via the direct production of adult phase transgenic citrus trees.


RESULTS
Factors important for promoting shoot regeneration from internode explants from adult phase citrus trees were identified and included a dark incubation period and the use of the cytokinin zeatin riboside. Transgenic trees were produced from four citrus types including sweet orange, citron, grapefruit, and a trifoliate hybrid using the identified factors and factor settings.


CONCLUSIONS
The critical importance of a dark incubation period for shoot regeneration was established. These results confirm previous reports on the feasibility of transforming mature tissue from sweet orange and are the first to document the transformation of mature tissue from grapefruit, citron, and a trifoliate hybrid.
U.S. Horticultural Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Ft. Pierce, Florida, USA.
Mizuri
M
Marutani-Hert
Kim D
KD
Bowman
Greg T
GT
McCollum
T Erik
TE
Mirkov
Terence J
TJ
Evens
Randall P
RP
Niedz
D060054:Agrobacterium / Q000502:physiology*; D015139:Blotting, Southern; D032083:Citrus paradisi / Q000235:genetics* / Q000382:microbiology; D032084:Citrus sinensis / Q000235:genetics* / Q000382:microbiology; D003470:Culture Media; D003624:Darkness; D018517:Plant Roots / Q000235:genetics* / Q000382:microbiology; D018547:Plant Stems / Q000235:genetics* / Q000382:microbiology; D030821:Plants, Genetically Modified; D016133:Polymerase Chain Reaction; D012038:Regeneration; D014170:Transformation, Genetic; D014197:Trees / Q000235:genetics / Q000382:microbiology
D003470:Culture Media