Description
| Abstract: | Commercial cultivars of citrus are mostly hybrids or mutants selected for specific desirable characteristics such as seedlessness. Such citrus must be propagated asexually. The long juvenility also makes genetic improvement through sexual cross breeding and hybrid evaluation a lengthy process. The present study was undertaken to define, evaluate and optimize conditions to propagate citrus via tissue culture and to transform citrus using Agrobacterium tumefaciens and microprojectile bombardment. Shoot tips of 1 millimeter obtained from Swingle citrumelo were successfully cultured to develop into plants on hormone free MS medium. Sixty percent of the shoot tips cultured were regenerated into plants and all plants were successfully established in soil. Root and stem explants regenerated numerous shoots when exposed to 5 - 10 milligrams per liter benzylaminopurine (BAP) for 48 hours and were subsequently culture on a hormone free medium. A BAP shock caused more stem explants to produce shoots while the number of shoots produced per stem explant remained the same. Root explants produced more shoots per explant when shocked with BAP. All these effects were seen only when the explants were planted vertically on the medium; horizontally cultured explants failed to regenerate. Citrus tissue tolerated kanamycin up to 100 milligrams per liter in culture medium. Genetic transformation of citrus via Agrobacterium tumefaciens and the biolistic method were achieved. Two plants confirmed to be transformed by engineered Agrobacterium tumefaciens strain LBA4404 carrying the marker genes for kanamycin resistance and B-glucuronidase activity were obtained from root explants. No transformed plants were obtained from co-cultivated stem explants or shoot tips. Agrobacterium tumefaciens strain A281 was the most effective in tumor formation in intact plants. The conditions for maximum transformation of citrus suspension cultures via the biolistic process were when the cells were placed at a distance of 4.7 centimeters and bombarded at a helium pressure of 1100 pounds per square inch in 27 - 29 inches Mercury vacuum. A period of 48 hours after bombardment was optimal for observing transient GUS expression. In conclusion, this study developed a rapid method to mass propagate citrus and opened up avenues for genetic transformation of citrus. |
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| Item Description: | Vita.
"Major subject: Horticulture." |
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| Physical Description: | xii, 118 leaves : illustrations ; 28 cm |
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| Bibliography: | Includes bibliographical references. |
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