Graduate Thesis Or Dissertation


Developing Tools for Hardy Hibiscus and Lilac Breeding: Quantile Regression, Cytogenetics, Interspecific Hybridization, Somatic Hybridization, and Marker-Trait Association Public Deposited

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  • Hibiscus and lilacs (Syringa spp.) are economically important nursery crops in the US that accounted for 4.5 million units ($30 million) and 2 million units ($20 million), respectively (USDA, 2016). To maintain and expand the market share of ornamental plants such as lilacs and Hibiscus, novel performance, floral ornamental value, reduced fecundity, and longer flower season are preferred. Interspecific hybridization has been widely used in ornamental plant breeding because hybrids were found to express novel traits, combine positive attributes of parents, transgressive segregation, and reduced fertility or even sterility. However, hybrid sterility has been shown to be inconsistent and is dependent on relatedness of parents among other factors. In some cases, hybrid plants retain a low level of fertility and the reduced or partial fertility could be further used for gene introgression, multiple-trait combination, unexpected phenotypes, and ploidy manipulation. In this research, I estimated the fertility of two large-flower interspecific hybrid Hibiscus cultivars, Lohengrin and Resi (H. syriacus x H. paramutabilis). A BC1F1 population from backcrossing between the two hybrid cultivars and double flower H. syriacus were created to combine large flower trait and double flower phenotype. In the population, a negative relationship between flower size and petal number was observed and thresholds based on quantile regression were used to simultaneously select plants with larger flowers among all different petal numbers. Hybrid cultivars were demonstrated to be useful to increase flower size, as progeny showed transgressive segregation at rates of 28.76% and 64.4% for ‘Lohengrin’ and ‘Resi’, respectively. All parent plants used in this research were tetraploid (4x) but hexaploid (6x) progenies of ‘Resi’ were observed at a rate of 78%. The higher ploidy, due to unreduced gametes from ‘Resi’, contributed to the larger flowers observed. In another study, an interspecific hybrid F1 population of dwarf lilac (Syring meyeri ‘Palibin’ x S. pubescens ‘Penda’ Bloomerang® Purple) was created and was subjected to Genotyping-By-Sequencing (GBS) analysis and phenotyped for level of reblooming in a season (remontancy). A total of 20,730 SNP markers from GBS were used in marker-trait association to find remontant-specific marker(s) without marker position information. Two SNP markers, TP70580 (A locus) and TP82604 (B locus), were correlated with remontancy. Accumulation of recessive alleles of the two loci (a and b) was positively related to increased reblooming. For example, 87% of aabb plants are true-remontant, and only 9% are non-remontant. By contrast, 100% of AaBB plants are non-remontant. These two SNP markers associated with remontancy are suitable for future breeding purposes and the current approach also demonstrates the feasibility of developing a marker-assisted selection (MAS) of woody ornamental plants that lack a reference genome or extensive sequence information, though further marker development and validation is required. In this study, we demonstrated the value of interspecific hybridization and hybrid cultivars for hardy Hibiscus breeding in many aspects. We also demonstrated a simple process of the non-reference-genome-reliant molecular markers to assist the remontancy selection for interspecific hybrid dwarf lilacs. In the Hibiscus protoplast funsion study, callus from nine cultivars of H. moscheutos, H. rosa-sinensis, and, H. syriacus were generated. Callus of H. rosa-sinensis ‘Red Cape’, H. rosa-sinensis ‘Legendary Heart’, H. moscheuto ‘Cranberry Crush’, H. moscheutos ‘Robert Fleming’, H. syriacus ‘Diana’, and H. syriacus ‘Buddha Belly’ were used in protoplast extraction by cellulous enzyme digestion because of their vigor. Unfortunately, no protoplast or cultivated cell survived three days after enzyme treatment. However, for untreated callous, we found the two H. syriacus cultivars showed strong regeneration ability from petiole to callus to shoot, in a modified-MS medium which was designed for H. rosa-sinensis. With this discovery, the modified MS medium, specific to H. rosa-sinensis, is recommended for H. syriacus tissue culture in furthering research purposes. Since callus stimulation of these cultivars from three different Hibiscus species all succeeded, we recommend the modified medium for callus stimulation of other Hibiscus species.
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  • Ongoing Research
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  • 2018-12-21 to 2021-01-22



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