title: Risk assessment of transgenic apomictic tetraploid bahiagrass, cytogenetics, breeding behavior and performance of intra-specific hybrids.
abstract: Pollen-mediated gene transfer from stress tolerant or herbicide-resistant transgenic plants may cause environmental or agronomic problems. Apomictic seed production found in some bahiagrass cultivars may serve as a natural transgene containment system. Under greenhouse conditions, the average gene transfer frequency from an herbicide-resistant apomictic tetraploid to a population of sexual diploid bahiagrass genotypes or apomictic tetraploid bahiagrass was 0.16% when the transgenic pollen donor was placed at 0.5-1.5 m distance from the non-transgenic pollen receptors. The herbicide-resistant hybrids were characterized for transgene integration, expression and ploidy, by Southern blot analysis, immuno-chromatography and flow cytometry, respectively. Hybrids resulting from open pollination of non-transgenic diploid female plants with transgenic tetraploid male plants were triploids or near-triploids, with 2n = 26-34. These hybrids displayed a wide range of phenotypic variability, including some non-persistent or non-flowering dwarf-type hybrids with good vigor, or hybrids with vegetative growth similar to non-transgenic plants, but with significantly reduced seed set. Non-flowering aneu-triploids with good vigor/field performance will provide the highest level of transgene containment. Embryo sac analysis of pollinated spikelets confirmed a high proportion of aborted ovules. An apospory-linked RFLP marker was detected in 13 of the 15 near-triploid hybrids. All flowering aneuploid hybrids displayed significantly reduced seed set, and none of the sexual near-triploid hybrids produced any seeds. All tetraploid gene transfer events carried the apospory-linked RFLP marker, suggesting that despite the presence of the aposporus locus, a low degree of sexuality co-exists in apomictic tetraploid cultivars. Thus, tetraploid apomictic bahiagrass does not provide complete transgene containment, although intra-specific gene transfer is drastically reduced compared to sexually reproducing perennial grasses.
authors.affiliation: Plant Molecular and Cellular Biology Program, Agronomy Department, Genetics Institute, IFAS, University of Florida, Gainesville, FL, USA.
authors.forename: Sukhpreet
authors.initials: S
authors.lastname: Sandhu
authors.forename: Victoria A
authors.initials: VA
authors.lastname: James
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Quesenberry
authors.forename: Fredy
authors.initials: F
authors.lastname: Altpeter
mesh_terms: D035264:Flowers / Q000235:genetics / Q000254:growth & development; D051456:Gene Flow; D022761:Gene Transfer, Horizontal; D006823:Hybrid Vigor; D006824:Hybridization, Genetic; D031781:Paspalum / Q000235:genetics* / Q000254:growth & development; D030821:Plants, Genetically Modified / Q000254:growth & development; D011058:Pollen / Q000235:genetics; D012150:Polymorphism, Restriction Fragment Length; D011123:Polyploidy; D019076:Transgenes
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