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Developmental biology of Exacum Styer Group pollen as related to haploid induction

University of British Columbia

Exacum Styer Group, a group of interspecific hybrids, possesses several valuable traits for ornamental use. However, current production techniques are limited to asexual reproduction of selected genotypes. Typically, inbred line development is highly desirable for commercial introduction of F1 hybrids as well as to facilitate genetic research. Unfortunately, this group suffers from severe inbreeding depression, precluding sexually derived inbred lines. In order to avoid inbreeding depression, double haploid plant development is one alternative approach. Therefore, this research developed fundamental information related to the successful application of this technology. Initially, fourteen genotypes were evaluated for pollen viability ranging from 0% to 80.5%. Three genotypes, with different levels of pollen viability, were selected and characterized for microsporogenesis, microgametogenesis, pollen morphology, and chromosome number. Microsporogenesis was normal among all three selected genotypes. However, the low fertility genotype and sterile genotype did not complete normal microgametogenesis and were found to have abnormal exine structure, perhaps indicating a dysfunctional tapetum layer. In contrast, the fertile genotype completed microgametogenesis, produced normal exine, and produced functional pollen grains. At anthesis, pollen was shed at the bi-nucleate stage. The chromosome numbers of the three genotypes evaluated ranged from 50 (fertile genotype) to 66 (low pollen viability). The individual chromosomes ranged in size from 0.3 μm (dot-shaped) to 2.65 μm (rod-shaped) with all three genotypes containing each form. Following characterization of pollen development, reprogramming treatments (e.g., temperature, mannitol, media composition and plant growth regulators) to induce haploid embryogenesis were applied at the mid uninucleate to early binucleate stage. After cold treatment (10°C) for 7 days, microspores maintained normal nuclei development without symmetrical divisions observed, suggesting that no androgenic switch occurred. Furthermore, heat treatment (35°C) for 4 days induced nuclei degradation and microspore non-viability. In addition to temperature treatments, mannitol treatments did not induce symmetrical divisions. When anthers were cultured under common temperature treatments, regardless of media composition, nuclei displayed a similar response indicating temperature was more effective in influencing nuclei development than media composition. Three different auxin and cytokinin combinations were evaluated on androgenic callilembryo induction. However, none of the combinations successfully induced calli/embryo formation.

Text

2010-01-08

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http://hdl.handle.net/2429/17885

Plant Science

University of British Columbia

UBCV

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