Thesis (M.S.)--California Polytechnic State University, 2009. / Mode of access: Internet. Title from PDF title page; viewed on April 30, 2009. Major professor: Terry Smith, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Agriculture with a specialization in Soil Science." "March, 2009." Includes bibliographical references (p. 37-40). Also available on microfiche.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Engineered nanomaterials (ENMs) are currently used in a wide range of manufacturing processes and applications thanks to the numerous technical and economic benefits derived from the incorporation of ENMs in these processes. Accompanying these benefits are the potential toxicity of ENMs to humans and the environment. Previous research has shown that ENMs display strong toxicity to plants. Earlier research suggested that physicochemical properties of ENMs such as their size, shape, and surface properties considerably affect toxicity; however, the unique physicochemical properties of ENMs affect their phytotxicity to plants is still unknown. This research evaluated the phytotoxicity of silver and gold nanoparticles to lettuce plants in both sand and hydroponic conditions by monitoring a wide range of plant physiological parameters after their exposure to these nanoparticles with two coating materials (citrate and polyvinylpyrrolidone) and three shapes (sphere, wire and plate) at 200 and 1000 µg/L concentrations. The result from lettuce in hydroponics showed that spherical silver or gold nanoparticles with both coatings did not affect biomass significantly, but both of silver and gold nanoparticles at 1000 µg/L slightly reduced the biomass compared to the control lettuce. The effect on root leakage was similar, but spherical silver nanoparticles had slightly higher damage due to root leakage than gold nanoparticles at the same concentration. The lettuce treated to citrate-coated gold nanoparticles significantly reduced chlorophyll content compared to citrate-coated silver nanoparticles. Secondly, when it came to the surface coating, the plant exposed to 1000 µg/L spherical citrate- coated silver or gold nanoparticles had higher root leakage compared to PVP-coated nanoparticles. Both of 1000 µg/L spherical citrate-coated silver nanoparticles and gold nanoparticles significantly reduced chlorophyll content compared to PVP-coated nanoparticles. Thirdly, for different shapes of PVP-coated silver nanoparticles, the plant exposed to plate shaped and sphere shaped silver nanoparticles had significantly lower biomass compared to the wire shaped silver nanoparticles. The plant exposed to spherical silver nanoparticles had the lowest chlorophyll content between plate shaped and wire shaped silver nanoparticles. In addition, the result from lettuce in sand medium showed that the biomass production and the root leakage showed no significant difference between spherical citrate-coated, spherical PVP-coated, and silver ions at 200 µg/L. In conclusion, different nanoparticles affected different physiological processes of plants differently.

Orientador: Marcel Agenor Pavan / Banca: Renate Krause Sakate / Banca: Francisco Murilo Zerbini Junior / Banca: Olivier Le Gall / Banca: Ivan G. Maia / Resumo: A família Sequiviridae é constituída por dois gêneros: Waikavirus e Sequivirus. Os vírus apresentam partículas isométricas com aproximadamente 30nm de diâmetro e uma única fita de RNA sentido positivo, sendo que o genoma dos waikavírus é poliadenilado e dos sequivírus não. Dandelion yellow mosaic virus (DaYMV) foi relatado infectando alface em diferentes países da Europa e classificado no gênero Sequivirus, porém dados moleculares não estão disponíveis para este vírus. No Brasil, um vírus isométrico infectando alface foi isolado por Marinho et al., (1982) no Distrito Federal e denominado de Lettuce mottle virus (LeMoV). Um provável isolado deste vírus isométrico foi descrito mais tarde no estado de São Paulo por Stangarlin (1995), sendo encontrado frequentemente em infecções mistas com o Lettuce mosaic virus (LMV). Em ensaios de microscopia eletrônica utilizando antissoro policlonal específico para Dandelion yellow mosaic sequivirus (DaYMV) e extrato foliar de plantas infectadas pelo LeMoV, foi verificada uma reação sorológica parcial (Chaves, 1999), indicando que o LeMoV possivelmente seria um membro do gênero Sequivirus, família Sequiviridae. Um protocolo funcional de purificação tanto para o LeMoV como para o DaYMV foi desenvolvido e sequências parciais do genoma de ambos os vírus foram obtidas usando preparações virais purificadas e... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The Sequiviridae family is constituted by two genus: Waikavirus and Sequivirus. The virus have approximately 30nm of diameter and a single-stranded of positive sense RNA. The genome of waikavirus is polyadenylated and of sequivirus not. Dandelion yellow mosaic virus (DaYMV) was reported in different countries of the Europe infecting lettuce and classified in the Sequivirus genus however, molecular data are not available for this virus. In the region of Federal District, Brazilan isometric virus infecting lettuce was isolated by Marinho et. al., (1982) and called of Lettuce mottle virus (LeMoV). Probable a strain of this isometric virus was described later in the Sao Paulo state by Stangarlin (1995), frequently found in mixed infections with the Lettuce mosaic virus (LMV). Using specific polyclonal antiserum for Dandelion yellow mosaic sequivirus (DaYMV) and foliar extract of plants infected for the LeMoV, a partial serological reaction was verified for this virus (Chaves, 1999), indicating that the LeMoV could be possibly a member of Sequivirus genus, Sequiviridae family. A functional protocol of purification was developed for LeMoV and DaYMV and partial genome sequences for both virus was obtained using virus purified preparation and degenerated primers for the Sequiviridae family. Sequences of the LeMoV-AF197 and the DaYMV-DSM2 were analyzed and showed a high identity with other members of the family. Universal primers that detect both viruses and specifics primers for LeMoV and DaYMV were used in diagnosistic tests based on RT-PCR. The specific primers amplified one fragment of 300bp for the LeMoV and 331bp for the DaYMV, being highly specific for diagnosis because no antiserum with good properties are available for these viruses. Different sequivirus proceeding from Brazil (BR11), Chile (Ch36), Holland (DSM2) and France (2227) were also evaluated in this work... (Complete abstract click electronic access below) / Doutor

Experiments were conducted with lettuce at the field and in the glasshouse at the Hatfield Experimental Farm, University of Pretoria. The objectives of the study were to evaluate the performance of selected crisphead lettuce cultivars in relation to yield and quality performance and to investigate which level of nitrogen can produce high quality transplants. In the lettuce cultivar trial, fifteen crisphead lettuce cultivars were grown, during March to May 2004. The experiment was laid out as a randomised complete block design with four replications. At harvest, the centre 20 plants were cut for yield determination and five uniform plants were then cut longitudinally for head quality characteristics. For each cultivar, compactness and uniformity were also evaluated and the number of days to maturity was recorded. Among the cultivars tested, the best yielding cultivars were Dual Purpose (46.8 t•ha-1), Great Lakes (45.8 t•ha-1), Mohawk (44.3 t•ha-1) and Victory (43.9 t•ha-1). Poor yielding cultivars were Taina (30.5 t•ha-1), Cannon (31.5 t•ha-1), Summer Time (32.1 t•ha-1) and Classic (33.2 t•ha-1). Del Rio was the best disease resistant cultivar, producing 100% marketable heads. All cultivars tested had good compactness and uniformity with the exception of Great Lakes 659. Early-maturing cultivars were ready 60 days after transplanting. Seeds of the lettuce cultivar ‘Aviram’ were sown, in the nitrogen nutrition of lettuce transplant’s trial. Two days after seeding, the seedlings were fertigated every second day by floating the trays in the plastic-lined tubs containing nutrient solution at 0, 30, 60,90 and 120 mg•L-1 N until field capacity was reached. Transplants produced with 0 N grew poorly, regardless of the sampling date. Nitrogen at 120 mg• L-1 improved the response of shoot growth, plant height and leaf area, but adversely affected root growth. In general, relative growth rate was improved while net assimilation rate was reduced as N level increased. Root: shoot ratio decreased with applied N. The largest values of root: shoot ratio were obtained with 0 N. Both specific leaf area and leaf area ratio increased with applied N. Leaf mass ratio improved, while root mass ratio was reduced as N levels increased. At 35 days after sowing, leaf tissue N increased from 0.43 to 4.15 mg•kg-1 with N applied. Only 25% of the plants produced without N could be pulled from the seedling trays, whereas 90% could be pulled when 90 mg•L-1 N was added. This work suggested that at least 90 mg•L-1N, supplied via floatation irrigation was required to produce a transplant with sufficient roots for ease of pulling. Applying 90 mg•L-1 N, resulted in improved root and shoot growth, resulting in high quality transplants. / Dissertation (M Inst Agrar (Horticulture))--University of Pretoria, 2007. / Plant Production and Soil Science / unrestricted

No description available.

No description available.

No description available.

No description available.

Published Article / Direct feeding damage to head lettuce (Lactuca sativa L.) by varying aphid populations in two differently constructed shadehouse structures (fully- and partially covered) was examined. Fresh lettuce head weight, the number of lettuce leaves formed, and the number of lettuce leaves infested with aphids were compared between the two structures. Warmer months showed a significant lower fresh lettuce head weight in the fully covered structure with more aphid-infested leaves. During June/September, the mean number of aphid-infested leaves and aphid infestation levels were significantly higher in the partially covered structure. Visible feeding damage to the lettuce crop was restricted, but asymptomatic damage in terms of a decrease in head weight did occur under severe infestation levels.