Master of Science, The Ohio State University, 2015, Horticulture and Crop Science

Begonia is one of the most speciose genera of angiosperms, with over 1500 species distributed throughout tropical and subtropical regions; it is also a very important ornamental group of plants displaying a high degree of morphological diversity. This genus is a priority for conservation and germplasm development at the Ornamental Plant Germplasm Center located at The Ohio State University, which currently holds approximately 200 accessions, maintained primarily as clonal plants. In an effort to expand germplasm work in seed storage of Begonia, and in response to a scarcity of published information about begonia seed biology we initiated a project to develop baseline information about germination, dormancy, and stress tolerance of begonia seeds. Because of the extremely small size of begonia seeds (ca. 200 µm) I adapted germination and viability testing protocols typical of Arabidopsis research, to develop relatively efficient quantitative protocols for seed studies. Using this methodology seeds can be routinely germinated on 1% agar plates at 25°C and 16 hours light. To examine the variation in seed characteristics among Begonia accessions in the collection, I selected six species from diverse environments and from different sections of the genus for which we had abundant seed and compared their germination patterns in response to temperature and light, tolerance to high humidity/high temperature stress, and dormancy. I have determined that begonia seeds are desiccation-tolerant (orthodox), require light for germination (photoblastic), germinate under a wide range of temperatures, and mostly appear to lack any strong dormancy — depending on species, and are tolerant of various level(s) of stress. I found that Begonia ulmifolia, B. fischeri, and B. dregei are tolerant to high levels of stress (120 hours at 41°C) whereas B. boliviensis, B. grandis subsp. evansiana and B. subvillosa are less so. In addition, B. dregei appears to have some dormancy, which was observ (open full item for complete abstract)

Committee: Pablo Jourdan (Advisor); Mark Tebbitt (Committee Member); Mark Bennett (Committee Member); Claudio Pasian (Committee Member) Subjects: Agriculture; Experiments; Horticulture; Plant Biology; Plant Sciences

Doctor of Philosophy, The Ohio State University, 2007, Horticulture and Crop Science

Ambrosia trifida (giant ragweed) is a North American native summer annual that has become one of the most problematic weeds in the eastern Corn Belt. Management of A. trifida has been challenging in part because of its temporal seedling emergence pattern. In agricultural fields, seedling emergence continues sporadically throughout the growing season. Studies were conducted to 1) determine characteristics of seed dormancy loss in the natural environment, 2) determine the seed dormancy mechanism associated with prolonged seedling emergence, 3) model seedling emergence in agricultural fields, and 4) elucidate the maternal effects on seed bank persistence. Seed dormancy loss in the natural environment occurred in response to cold-moist conditions and involved the sequential reduction of embryo and coat-imposed dormancy. Embryo dormancy and its interaction with soil temperature was the dormancy mechanism primarily responsible for the prolonged seedling emergence pattern of agricultural populations. Two integrated Weibull models described seedling emergence as a function of hydrothermal time in tilled and no-tillage environments and two locations in Ohio. Models indicated emergence was insensitive to periods of no rainfall and that emergence occurred during two intervals separated by a period of little emergence around May 1. The biphasic emergence pattern was explained by diverse emergence times among the progeny of particular maternal plants. Maternal families characterized by smaller seeds were more likely to emerge after May 1st compared to maternal families characterized by larger seeds. Furthermore, maternal families with smaller seeds were more likely to remain viable in the soil after one emergence season compared to maternal families with larger seeds. Seed bank longevity was influenced by dispersal unit maturation time and maturation effects varied between years. The most persistent fraction of the seed population originated from small-seeded individuals at a pa (open full item for complete abstract)

Committee: Regnier Emilie (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2003, Horticulture and Crop Science

Common groundsel (Senecio vulgaris L.) is an annual weed of Mediterranean origin that has become a worldwide pest in many crop production systems, including small fruit crops like strawberry. Management of common groundsel has been difficult because of its tolerance of many control measures and resistance to some herbicides, and because of inadequate or conflicting information about its biology. Studies were conducted in Ohio to determine the effect of common groundsel's maternal environment on seed dormancy, describe the pattern of seedling emergence and seed persistence, and to evaluate the response of common groundsel and strawberry to herbicides. Experiments were conducted using local seeds and seeds collected along a 700-km transect from Michigan to Kentucky. Freshly matured seeds collected from sites along this transect differed in germination response to temperature, but when plants from these sites were grown in a common environment the seeds responded uniformly to temperature. In growth chamber studies, seeds maturing on plants growing in cold short day conditions were mostly dormant whereas seeds produced on plants in warm long day conditions were mostly non-dormant. Changing temperature conditions from warm to cold increased seed dormancy, especially when the change occurred in early reproductive stages. The dormancy status of buried seeds varied throughout the year, mostly in response to soil temperature. Seedling emergence was limited by both rainfall and temperature but there was an interaction with tillage. A logistic regression model demonstrated that in tilled soil, emergence was stimulated by small amounts of rainfall, but in no-till conditions about ten-times as much rainfall is required to stimulate emergence. Nearly all buried seeds germinated or died during two years of burial in soil. In newly established strawberries, common groundsel was controlled with the herbicide sulfentrazone (N-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5 (open full item for complete abstract)

Committee: Doohan Douglas (Advisor) Subjects: Agriculture, Agronomy

Master of Science (MS), Ohio University, 2012, Environmental and Plant Biology (Arts and Sciences)

Disturbance such as forest management is thought to promote invasive species spread. This study uses population demography to address the spread of the invasive species Ailanthus altissima, Alliaria petiolata, and Microstegium vimineum in forested sites in southeast Ohio. Invasive species populations were examined in the silvicultural treatments prescribed burn and timber harvest, plus control plots with no management. Seed rain, seedling establishment, and the soil seed bank was studied for each population. All invasive seeds formed a persistent seed bank and experienced seasonal dormancy, but the proportion of dormant seeds varied among species (p<0.05). Slope aspect effected seed survivorship and dormancy (p<0.05) for each species. Dormancy for each species showed no relationship or a weak relationship with time since seed burial. Invasive populations expanded at a constant rate among treatments, and invasive seeds changed dormancy conditions seasonally to allow for germination during favorable conditions, which may contribute to invasive ability.

Committee: Glenn Matlack PhD (Advisor); Stefan Gleissberg PhD (Committee Member); Harvey Ballard PhD (Committee Member) Subjects: Botany

Doctor of Philosophy (PhD), Ohio University, 2006, Plant Biology (Arts and Sciences)

Eastern deciduous forests include a remarkable number of plants that are utilized widely for their medicinal properties. However, the long-term sustainable use of medicinal forest plants requires that methods be developed for restoring and cultivating them in natural and semi-natural settings. This study examined the seed regeneration biology of several perennial forest herbs that are internationally traded in the increasingly lucrative botanical medicines industry. Specific objectives were to: (1) determine how environmental cues (temperature, light, substrate, and burial) regulate dormancy-break and carry-over in seed populations of Actaea racemosa (black cohosh), Hydrastis canadensis (goldenseal), and Sanguinaria canadensis (bloodroot); (2) experimentally evaluate seedling recruitment probabilities of A. racemosa, H. canadensis, S. canadensis, and Panax quinquefoliusin different forest microenvironments defined by varying levels of leaf litter and opposing topographic positions; (3) classify seed dormancy and determine optimum germination temperatures for Collinsonia canadensis (stoneroot) and Dioscorea villosa (wild yam); and (4) quantify survival rates and dormancy-levels of A. racemosa and H. canadensis seed populations stored in artificial conditions. Results from these studies showed that: (1) germination probabilities can vary widely when seeds experience different environmental cues, although temperature is the primary factor regulating dormancy-break and germination; (2) some perennial forest herbs can form persistent seed banks and spread germination across time; (3) leaf litter and topographic position can act as ecological filters during early life-history stages; and (4) storing seed populations prior to outplanting reduces viability in H. canadensisseeds and deepens dormancy levels in A. racemosa seed. Recommendations are made for cultivating, managing, and restoring these species in the eastern deciduous forest landscape.

Committee: Brian McCarthy (Advisor) Subjects: