Grant Information
| Knowledge Area | Subject of Investigation | Field of Science | Percent |
|---|---|---|---|
| 204 - Plant Product Quality and Utility (Preharvest) | 920 - Orange | 1080 - Genetics (excludes breeding) | 40% |
| 203 - Plant Biological Efficiency and Abiotic Stresses Affecting Plants | 910 - Grapefruit | 1000 - Biochemistry and biophysics | 30% |
| 212 - Pathogens and Nematodes Affecting Plants | 999 - Citrus, general/other | 1160 - Pathology | 30% |
Using factors potentially critical for these types of tissues such as tree preconditioning, Agrobacterium vector, media formulation, in vitro environmental conditions, explant type, disinfestation treatment, growth regulators, and genotype in an attempt to transform mature tissue.
This project is related to Objective 1 of this in-house project: Develop new citrus scion and rootstock varieties. Citrus transformation is currently limited to the use of juvenile tissue. However, this results in trees that require many years before flowering. Transformation of mature tissue would reduce the time to flowering substantially. This provides at least two benefits: 1) traits only visible in mature trees could be assessed (e.g., fruit quality) and 2) the trees could for breeding (i.e., hybridization). Progress in the various components of a mature citrus transformation system is as follows: 1. Source of mature tissue. Four populations of adult phase trees were maintained in the greenhouse including Valencia sweet orange/Sun Chu Sha (73 trees), Ruby Red grapefruit/US812 (62 trees), US-942 citrange rootstock/Cleo (32 trees), Calamondin (31 trees), and Etrog Arizona 861- S1 citron (67 trees). 2. Decontamination protocol. A decontamination protocol was developed that results in more than 90 percent clean explants, sufficient for tissue culture studies and practical applications. 3. In vitro bud emergence and growth. A system was developed for the production of in vitro adult phase shoots from cultured nodes of greenhouse trees. Factors important in bud emergence and growth were identified and a system developed to initiate bud emergence and growth with reduced leaf drop. 4. Shoot regeneration from mature tissue explants. A system was developed for the production of shoots from cultured internodes from greenhouse trees. Factors (e.g., pre-incubation tissue treatments, plant growth regulators, and incubation conditions) important in bud formation and shoot growth were identified and a system developed that is suitable for sweet orange, grapefruit, Calamondin, and US-942 (Note: citron was just recently added so has not yet been tested). The system results in shoot and bud formation in 70-90 percent of the explants. 5. Agrobacterium-mediated transformation of mature tissue explants. Transformation of mature internode explants from greenhouse trees has been demonstrated in grapefruit and US-942 using the beta-glucuronidase reporter gene. Though these are the first experiments, the results document that we have a functional mature tissue transformation system. Transformed plants were obtained for US942, citron, grapefruit, and sweet orange.