An integrated in vitro and greenhouse orthotropic clonal propagation system for Theobroma cacao L

Two novel methods are described to stimulate intensive and sustained orthotropic (vertical, juvenile) shoot production in softwood and semi-hardwood Theobroma cacao L. stock plants, derived from tissue culture of floral staminodes via primary and secondary somatic embryogenesis.;The first stock plant method consisted of development of softwood stock plants in a bench top modified hedge. Under the specific conditions of the current study, the estimated production of orthotropic rooted cuttings from softwood stock plants maintained as a bench top clonal garden was estimated to range between 825 and 1,012 rooted cuttings m-2·year -1.;The second orthotropic shoot production method involved the bending to horizontal of the main trunk of semi-hardwood stock plants from 9 to 12 months after acclimation, release of axillary and adventitious orthotropic meristems from the bent trunk, and repeated harvest by periodic light pruning of orthotropic shoots for rooting material. Using the bending method, semi-hardwood stock plants yielded on average over 300 single and few node orthotropic stem cuttings per year, or approximately 500 m-2 ˙year-1 at the stock plant density tested.;Overall, the softwood orthotropic stock plants produced 1.5 times more plants per given unit of space and time than the bent semi-hardwood stock plants. Softwood stock plants are compact and have shorter chupons and leaf laminae, as well as smaller stem diameters in comparison to bent semi-hardwood stock plants. Production of softwood stock plants requires a higher level of cultural management and propagation technique than those for bent semi-hardwood stock plants. Utilization of softwood stock plants in the current study significantly shortened the time necessary for greenhouse multiplication of vegetatively propagated orthotropic cacao plants compared to the utilization of bent semi-hardwood stock plants.;Comparison of development at the juvenile stage in a climate controlled greenhouse demonstrated that primary somatic embryos (1°SE) and secondary somatic embryos (2°SE) grew true to type as compared to seedlings. As well, orthotropic rooted cuttings from softwood stock plants (RC-SW) and orthotropic rooted cuttings from bent semi-hardwood stock plants (RC-SHW) grew true to type. All four orthotropic vegetatively propagated trees had the characteristic jorquette (whorl of plagiotropic fan branches) at the phase change from the juvenile orthotropic trunk to the mature plagiotropic canopy morphology.;These orthotropic clonal propagation methods may be adopted by germplasm banks, international cacao research centers, universities, private laboratories, as well as regional and local extension services and nurseries for use in international, regional, and local distribution schemes for elite or other newly developed clonal varieties of cacao or other instances where original stock plant material is limited or the orthotropic seminal tree architecture is desired. The use of the bending technique for semi-hardwood stock plants may be of particular utility to nurseries and growers interested in robust, on-farm propagation of clonal varieties that have orthotropic tree architecture and an orthogeotropic adventitious framework root system similar to that of a seminal tree.;A single line of somatic embryo plants that were genetically transformed by cocultivation with Agrobacterium tumefaciens strain AGL1 and containing the EGFP and NPTII genes were acclimated to the greenhouse. Non-destructive growth measurements were taken to compare the transgenic line and non-transgenic 2°SE plants during 18 months. Growth analysis of plant height, stem diameter, number of leaves and leaf area, as well as photosynthesis and excised root respiration measurements did not indicate any differences in these parameters between transgenic and non-transgenic SE-derived plants. EGFP expression was analyzed in seeds from two genetic crosses. One to one segregation of EGFP expression in the seeds indicated that the T-DNA was inserted at a single locus in this line. (Abstract shortened by UMI.)...