Doctor of Philosophy, The Ohio State University, 2008, Soil Science

Long-term plots located at Hoytville and Wooster experimental centers (OARDC, Ohio), combine no-till (NT) and plow till (PT) and continuous corn (CC), corn-soybean (CS) and corn-oats-meadow (COM) on soils of contrasting properties. A poorly drained Mollic Epiaqualf is present at Hoytville, and a well drained Typic Fragiudalf dominates at Wooster. To study the impact of agricultural management (NT and PT) and less intensive land uses (wooded and grassed areas) on soil properties and nutrient cycling, pedon description and sampling was conducted at both experimental sites, including one pedon each under forest, grass, and PT and NT under corn. Standard physicochemical and mineralogical characterization and micromorphological study of thin sections were conducted. At both sites strong structure, more bioturbation with lower bulk density and increased, highly connective macroporosity were found under NT. The soil C pool (up to 31 cm) was high in the forest and NT pedons at Wooster and in forest and grassed pedon at Hoytville; PT has the lowest values at both sites. Grass and NT soils sequestered C after 40yr at Wooster but NT and PT could not reach the original C value at Hoytville. Two others studies were conducted analyzing soil samples from the last two decadal soil samplings of the experiments to track the evolution of main soil nutrient concentrations, C and N pools and pH as affected by the mentioned tillage-crop rotations. At both sites C and N concentration and C and N pools were higher under CC and COM than CS due to the reduced amount and high decomposable residues. Carbon and N concentrations and C and N pool values were higher with NT than PT at both sites; C content and C pools stabilized with NT and increased with PT at the second sampling. At both sites under CS and COM the soils had higher pH and extractable bases related to lower N fertilizer rates and greater cation recycling by roots and residues. Cation retention was greater for NT than PT; soil avai (open full item for complete abstract)

Committee: Neil Smeck (Advisor) Subjects: Agriculture, Agronomy

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

Seed dormancy, germinability and storability are important aspects of seed quality determined by the genotype and environment during seed development. Lettuce is one of the most important vegetables in the world and high quality seed is required for successful crop establishment. However, seed thermoinhibition and photodormancy are two properties commonly affecting germination speed and uniformity of many lettuce genotypes. The main objectives of this study were to determine the effects that maternal plant conditions have on different aspects of lettuce seed quality such as germinability and storability. In separated experiments, ‘Tango' lettuce seeds were produced in contrasting conditions for the following environmental factors: i) water availability, ii) day-length, iii) light quality (red to far-red [R:FR] ratio), and iv) temperature. Restricted water availability during lettuce seed production had little effects on most aspects of seed quality, although a significant increase in seed weight and the production of fewer seeds per plant were observed. Additionally, water productivity (seed yield per volume of water consumed) increased significantly in response to restricted water availability, which is especially important for lettuce seed producers which are located mainly in arid regions. Seeds produced at higher temperatures (30/20°C vs. 20/10°C) had higher storability and lower thermoinhibition, photodormancy, and dry weight. Temperature effects on seed germinability occurred during the first phase of seed development (cell division and histo-differentiation), while effects on seed storability occurred at the last phase of seed development (maturation drying). The aspect of the maternal plant light environment that had the greatest effects on seed quality was the R:FR ratio. Seeds produced under higher R:FR ratios had higher germinability, poorer storability, lower sensitivity to external abscisic acid (ABA), and lower ABA concentrations. These effects occurre (open full item for complete abstract)

Committee: Mark Bennett (Advisor) Subjects: Agriculture, Agronomy

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

Color is an important attribute of processing tomatoes. Color and color uniformity are affected by yellow shoulder disorder (YSD), a ripening disorder that results in discoloration of the proximal end tissues of the fruit. We show lycopene content was reduced by 13-24% in juice from non-YSD tomato. Beta-carotene content was reduced by 4-8% in juice from YSD-affected tomato, although this reduction was not statistically significant. Quantification of carotenoid content was more precise by increasing biological replications rather than analytical replications. To assess genetic contributions to YSD, a color measurement module in the Tomato Analyzer software was tested to quantify color and color uniformity from digital images. This approach improved the efficiency of collecting data, provided high correlations with data collected by colorimeter, and improved estimates of genetic contributions to color. With increased precision and accuracy in measuring color, sampling strategies for higher carotenoid content can be optimized and the genetics of color uniformity in tomato can be uncovered. To elucidate the genetics of YSD, molecular markers were developed and exploited for breeding application. An advanced backcross population (BC2) derived from Solanum lycopersicum (OH88119) x S. pimpinellifolium (PI128216) was evaluated for color. Indices were developed to circumvent the highly correlated traits and to simplify the trait complexity based on principal component analysis. These indices capture the essential features of color intensity and color uniformity. The BC2 population was genotyped with 70 markers for QTL analysis. The population was selfed through four generations to generate an inbred backcross population (BC2S4), which was evaluated for the same traits and genotyped with the same markers as the BC2 population. An F2 population and elite varieties were evaluated for color to confirm the QTL. We found QTL for color intensity on chromosomes 2, 8, and 9, and a QT (open full item for complete abstract)

Committee: David Francis (Advisor) Subjects: Agriculture, Agronomy

Doctor of Philosophy, The Ohio State University, 2005, Horticulture and Crop Science

Research has extensively showed that pastures with complex composition can increase production in some situations. However, there is a general lack of information on the role of within species (intra-specific) diversity and its contribution to the ecological functionality of a community. This research used perennial ryegrass as a model plant to (i) quantify within- and between-cultivar variation of L. perenne cultivar blend BG34 on the basis of several morphological characteristics and forage yield; (ii) investigate the responses of relative yield and production components of individual genotype, and how this was affected by the treatments of genotype and defoliation; and (iv) evaluate the suitability of SSR (simple sequence repeats) and ISSR (inter simple sequence repeats) markers to differentiate the cultivars of L. perenne that comprise BG34 and investigate the genetic structure of pastures sown with BG34 ryegrass from dairy fields in Ohio. With 100 potted plants of the four cultivars investigated, within-cultivar variation accounted for 73-97 % of the total variation for the morphological traits (i.e. height, tiller number, erectness, leaf width and yield), and 13.4 to 89.9% of the variation could be attributed to genetic variation. A genotype treatment by defoliation treatment experiment was established with cloned plants of eight genotypes, which had different production and tillering potentials, it was found that plot production was linearly related to genotype diversity, and mixtures had significantly greater yield than monoculture on average. Frequent (3-wk) defoliation reduced grass yield by 12.7%, while the 60 mm height clipping reduced grass yield by 14.3%. In general, large genotypes were favored in mixtures and small genotypes were at disadvantage. With both SSR and ISSR markers, individuals of BG34 were correctly allocated to lines and cultivars with 80.9-86.7% accuracy. There were distinct differences between cultivars, suggesting the suitability of (open full item for complete abstract)

Committee: David Barker (Advisor) Subjects: Agriculture, Agronomy

Doctor of Philosophy, The Ohio State University, 2005, Horticulture and Crop Science

Studies were conducted at the plant, population, and community level to address questions concerning (1) seed germination in Alliaria petiolata (2) weed community composition and structure in response to tillage, rotation and herbicide, and (3) variation in Abutilon theophrasti. Alliaria petiolata seeds are dormant at maturity, requiring approximately 90 to 105 days cold-moist stratification at 4 to 5 °C for germination to occur. Mechanically scarified, and H2O2 and H2SO4 treated seeds germinated within 35 days when GA3 was applied exogenously. The composition of the weed-seedbank community was characterized 35 years after the implementation of a long-term study involving cropping sequence (continuous corn, corn-soybean, corn-oat-hay) and tillage system (conventional-, minimum-, and no-tillage). Values of S, J, and H' recorded for all combinations of the three-crop sequence were typically greater than the values of S, J, and H' reported for either the one and two-crop rotations. As the intensity of soil disturbance decreased, values for S increased. Mean germinable weed seed density was greatest in the no-tillage treatments across rotations and years. Results suggest that the weed seed community in a corn-oat-hay rotational system differs in structure and composition from communities associated with continuous corn and corn-soybean systems. There is concern that the widespread use of genetically-modified glyphosate-tolerant crops (GTCs) will alter agricultural weed community dynamics with respect to glyphosate-tolerance and emergence phenology. Species associated with individual tillage and rotation treatments were not different from species recorded in the same plots prior to the exclusive use of GTCs and glyphosate, suggesting that significant changes in weed community composition and structure have not occurred. Abutilon theophrasti is a noxious weed in modern row-crop agriculture. This study characterized the morphological, phonological, and genetic variation ve (open full item for complete abstract)

Committee: John Cardina (Advisor) Subjects: Agriculture, Agronomy

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

Doctor of Philosophy, The Ohio State University, 2003, Horticulture

The objectives of this study were to investigate the adaptability of the genus Salix to stressful conditions and to promulgate its ornamental potential. This research has focused on Salix's tolerance of natural and anthropogenic stresses, including flooded soils, soil compaction, heavy metals, and ozone pollution; all are common conditions in urban environments. I found that neither soil compaction nor flooding caused a significant reduction in the growth of willows, but that anaerobic conditions rapidly triggered a wide range of morphological adaptations. The copper and cadmium uptake study, conducted in a greenhouse hydroponic system, revealed a general tolerance of willows of increased metal in the solution and the translocation of metal into plant aerial organs; copper appears to be more toxic to plants and less mobile than cadmium. The response of Salix species to acute ozone exposure was studied in a fumigation chamber and it revealed marked interspecific differences; both ozone-sensitive and ozone-tolerant species were documented. The ornamental qualities of cut branches from twenty species and cultivars of shrubby willows were evaluated and described in detail, focusing on those attributes, and phenological sequence, important for the floral industry. More than fifty promising willow species for alpine and small urban gardens were selected based on multi-year observations. Their names were taxonomically verified, and they are presented with detailed descriptions, horticultural uses and requirements, and details of provenance.

Committee: Martin Quigley (Advisor) Subjects: Agriculture, Agronomy

Doctor of Philosophy, The Ohio State University, 2002, Horticulture and Crop Science

The tomato crop is an important source of carotenoids such as beta carotene and lycopene. These carotenoids play important roles in human health and nutrition. Consequently, humans benefit from the development of tomatoes with enhanced carotenoid content. High pigment genes, such as dark green (dg) and high pigment (hp) that result in higher levels of carotenoids are available. The effects of these genes on plant development are not well understood. In addition, their effects in other traits such as seed longevity and total antioxidant capacity (TAC) have not been evaluated. This study evaluated the effect of fruit development on seed quality of tomato varieties with different concentrations of carotenoids. Gibberellin and norflurazon (an inhibitor of carotenoid synthesis) effects on speed of germination of varieties with different concentrations of carotenoids were also evaluated. Fruits and seeds of these varieties were assayed for TAC using the Photo-induced Chemiluminescense (PCL) and the Total Equivalent Antioxidant Capacity (TEAC) methods. Results indicated that the effect of fruit development on seed germination depends on the genotype and that the low speed of germination characteristic of the high lycopene line is independent of the gradual accumulation of lycopene. Seeds of the high pigment line treated with norflurazon plus gibberellin germinated faster than the control indicating that abscisic acid (ABA) is involved in the low speed of germination of high lycopene genotypes. Fruits of the dg line had significantly greater antioxidant capacity than fruits of the recurrent parent. However, seeds of the recurrent parent had higher antioxidant capacity than seeds of the high pigment line as assayed by both PCL and TEAC methods, suggesting that antioxidants in the fruit may compete with antioxidants in the seed. In conclusion, genotypes carrying the dg gene result in a high content of lycopene and antioxidant capacity and have delayed seed germination possibl (open full item for complete abstract)

Committee: Mark Bennett (Advisor) Subjects: Agriculture, Agronomy