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theses

Chapter 1
Highbush blueberries (Vaccinium sect. Cyanococcus, family Ericaceae) are an important agricultural crop in the United States, as well as ecologically significant native shrubs in eastern hardwood forests and wetlands. The New York Metropolitan Flora Project has found that nearly all members of the heath family (Ericaceae) in the New York metropolitan area have been decreasing in range size over the past 100 years, with a corresponding decrease in abundance as well (Clemants & Moore, 2005). Additionally, morphological, ecological, and genetic differences within the genus complicate the taxonomy of Vaccinium, so the status of highbush blueberry, in particular, is not very clear. Highbush blueberry has recently been considered one species, Vaccinium corymbosum (Flora of North America; Vander Kloet 1980), but the highbush blueberries have been separated into as many as 12 different species over the years (Camp 1945). Some of this taxonomic confusion is due to the mix of diploids, tetraploids, and hexaploids within the genus, all showing different morphological and ecological characteristics (triploids do not generally survive (Vorsa & Ballington 2001). With estimates of polyploidy occurring in 30-80% of angiosperm species (Soltis & Soltis 2000), this is not an uncommon problem in botany today.
Stebbins (1971) suggested that parental diploid strains are more fit than their tetraploid descendants (WHY). The opposite hypothesis has also been presented, that polyploids may be more fit than diploid parents (Ortiz et al. 1992, Soltis & Soltis 2000) WHY. I hypothesize that tetraploid highbush blueberries will show higher fitness in a wider range of ecological conditions than diploid highbush blueberries.
I am currently investigating differences between native varieties of diploid and tetraploid highbush blueberry to (1) help define variation and establish whether there is gene flow between these two cytotypes; (2) explore ecological tolerances to determine fitness and evolutionary advantages and/or disadvantages of polyploidy; (3) determine the causes of the decrease in range and abundance of the native highbush blueberry (Vaccinium corymbosum); and (4) establish restoration protocols for highbush blueberry that can help preserve, improve, and restore the native populations of this economically and ecologically important native shrub.
Applications of these findings are critical to the ecological restoration community and industry, as appropriate genotypes for improving the nation’s natural resources are needed. The concern for appropriate genotypes to use in different ecological settings is an active area of research (Handel et al. 1994, Hufford & Mazer 2003). These investigations will assist in determining the cytotypes most useful for sustainable and resilient restored populations of this important understory species, as well as inform commercial and home growers of the best cytotypes for local conditions. These studies will add to our understanding of the putative ecological advantages of polyploidy in plants.

Chapter 2
Due to its ubiquitous presence in all green plant lineages, polyploidy (or whole-genome duplication) is being studied as an important factor in ecological and evolutionary trajectories in plants. The highbush blueberry (Vaccinium corymbosum L.) species complex contains diploids, tetraploids, and hexaploids, although it has been historically debated whether these cytotypes represent separate species or collectively constitute a single polymorphic taxon. Diploid and tetraploid cytotypes are sympatric in several New Jersey locales, but the ecological effects of mixed ploidy are unknown. Here, we conducted a greenhouse experiment testing whether diploid and tetraploid seedlings from natural populations respond similarly to different levels of soil pH, soil moisture, and additional soil mycorrhizae. Size measurements for stem length, numbers of leaves, and total biomass were recorded prior to the experiment, and then again after 6-7 weeks of treatment exposure.
Plants in the low pH (5.0) soil were significantly larger than those in the high pH (6.8) soil, regardless of ploidy. Under low pH conditions, tetraploids grew slightly larger than diploids, but under high pH conditions, diploids had significantly larger biomass. Neither ploidy nor the addition of mycorrhizae had any effect on plant size, but wet treatments produced plants with longer stems than did dry treatments. Wet treatments also had significantly more mycorrhizal colonization than dry treatments, though there were no significant differences in mycorrhizal colonization between treatments with liquid ericoid mycorrhizae added and control treatments. Diploids may have an ecological advantage under high soil pH conditions, and therefore may be better suited for restoration purposes in non-acidic soils.

Chapter 3
Polyploidy is a common phenomenon in plants that affects genetic variation and can lead to speciation. Vaccinium corymbosum (highbush blueberry) taxonomy is confounded by sympatric populations of diploid and tetraploid cytotypes. Although prezygotic isolating barriers are known to exist, the rate of interploidal mating in sympatric populations is unknown. Here, we use hand-pollinated interploidal crosses and comparisons of fruiting rate, seeds per berry, and seedling emergence rate to test the reproductive consequences of polyploidy in this species. Ploidal levels were confirmed with flow cytometry and crosses were confirmed with PCR analysis using 9 SSR markers. Diploid plants at two field sites in New Jersey were pollinated with tetraploid pollen and tetraploid plants in a greenhouse were pollinated with diploid pollen collected from the field sites. Homoploid crosses were used as controls.
Homoploid crosses produced viable seed, confirming successful pollination techniques both in the field and in the greenhouse. Homoploid crosses had significantly higher average fruiting rate, average seeds per berry, and average seedling emergence rate than heteroploid crosses. Tetraploid homoploid crosses had significantly more average seeds per berry than diploid homoploid crosses. Pollen ploidy was a significant factor in fruiting rate, seeds per berry, and emergence rate, although maternal ploidy was only significant in seeds per berry. Heteroploid crosses on diploid maternal plants had significantly higher fruiting rate than heteroploid crosses on tetraploid maternal plants, but had significantly lower average number of seeds. Heteroploid crosses were conducted on 734 flowers, 42 berries were produced, and three seedlings developed from these crosses, two of which were triploid, and one tetraploid. Due to a high rate of unreduced gamete production in diploid individuals, heteroploid crosses produce fruit with viable seed that contribute to the population structure and gene flow of this species complex.

ETD_9341

M.S.

Includes bibliographical references

doi:10.7282/t3-bzpr-8s40

ETD graduate

The author owns the copyright to this work.