PhD / In South Africa, tomato (Solanum /ycopersicum) is an important vegetable crop with considerable nutritional and economic value. Over the last decade, begomovirus (family Geminiviridae) infections associated with an upsurge of the whitefly vector, Bemisia tabaci, on tomato crops has become a serious threat to sustainable tomato production in South Africa. Begomovirus disease control in tomato is challenging and requires an integrated "pest" and "vector" management strategy, primarily based on the use of chemical and cultural practices aimed at reducing the virus vector as well as the use of resistant cultivars. Development of effective disease management practices for South Africa therefore requires detailed information on the complex vector-virus-host cropping system interactions. The aim of the study presented in this thesis was to investigate the South African whitefly vector/begomovirus/tomato-host pathosystem, with emphasis on the virus and vector diversity and distribution, and the identification of possible resistance sources. A survey of tomato-infecting begomoviruses was conducted during a six-year period (2006-2011 ). Techniques used to determine begomoviruses diversity included whole genome amplification using PCR, RCA (rolling circle amplification), conventional as well as next generation sequencing and development of a RCA-RFLP (restriction fragment length polymorphism) for rapid assessment of diversity. Sequence comparisons and phylogenetic analyses revealed the presence of three new monopartite begomovirus species, in addition to ToCSV, all of which belong to the African/South West Indian Ocean (SWIO) begomovirus clade. Recombination analysis indicated that all four tomato-infecting begomovirus species appear to be complex recombinants and suggests that they have evolved within the sub-Saharan Africa region, along with other African begomoviruses and that they are most likely indigenous to the region. Several weed species were also confirmed as symptomless begomovirus reservoirs, supporting their role in the emerging begomovirus epidemics in South Africa.

Orientador: Rumy Goto / Banca: Giuseppina Pace Pereira Lima / Banca: Antonio Carlos Maringoni / Banca: Rômulo Fujito Kobori / Banca: Nidia Majerowicz / Resumo: A enxertia é uma técnica utilizada com a finalidade de controlar patógenos de solo, como a R. solanacearum, porém em porta-enxerto resistente tem-se observado sintomas da doença no enxerto, devido a passagem do patógeno. A enxertia e a bactéria podem causar estresse na planta de tomateiro e algumas enzimas e o teor de fenóis podem ser usados como respostas bioquímicas a estes estresses. Para avaliar a eficiência desta técnica sobre a bactéria e na produção de tomateiro foram medidas, a incidência da doença, trocas gasosas das plantas, a atividade de algumas enzimas como superoxido dismutase (SOD), catalase (CAT), peroxidase (POD), fenilalanina amônia-liase (PAL), polifenoloxidase (PPO), teor de fenóis e produção em plantas de tomateiro 'Pizadoro' pé-franco e enxertadas no porta-enxerto 'Guardião'. Para tanto foram realizados dois experimentos na Faculdade de Ciências Agronômicas da UNESP de Botucatu-SP e um experimento na Fazenda de ensino, pesquisa e produção (FEPP) em São Manuel, SP. No primeiro experimento foi avaliada a variação da atividade enzimática (SOD, CAT, POD, PPO) e teor de fenóis em mudas do tomateiro, em função dos métodos de enxertia Contato em bisel, Fenda garfagem, Encostia, enxerto pé-franco e cinco coletas das plantas, aos 0, 3, 6, 9 e 12 dias após a enxertia (DAE). No segundo, foram avaliadas a incidência da murcha bacteriana, trocas gasosas nas folhas, além da atividade das enzimas SOD, CAT, POD, PAL, PPO e teor de fenóis, aos 0, 2, 4, 6, 8 e 15 dias após a inoculação com R. solanacearum, em plantas enxertadas de tomateiro conduzidas em casa de vegetação. No terceiro experimento foram avaliados três métodos de enxertia (Contato em bisel, Fenda garfagem e Encostia) e pé-franco na produção de tomateiro sob ambiente protegido. O método Fenda garfagem é melhor... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Grafting is a technique used in order to control soil pathogens, such as R. solanacearum bacteria. The symptoms of the disease, however, have been observed in resistant rootstock, due to the passage of the pathogen to the graft. Both grafting and the bacteria can cause stress in tomato plant and some enzymes and phenols can be used as biochemical marker to this stress. In order to evaluate the efficiency of grafting to control the bacteria in the tomato yield, the disease incidence, plant gas exchange, phenol contents and the activity the enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO), as well as tomato fruit yield were measured. The study considered ungrafted and grafted tomato plants 'Pizzadoro' on rootstock 'Guardian' in two experiments carried out at the College of Agricultural Sciences, UNESP, in Botucatu-SP, and one experiment at the Farm of Teaching, Research and Production (FEPP), in São Manuel-SP. The enzymes activity of SOD, CAT, POD, PPO and phenol content in tomato seedlings were evaluated in the first experiment, as a function of the grafting methods Contact bevel, Cleft grafting, Supported grafting, graft ungrafted in five harvests at 0, 3, 6, 9 and 12 days after grafting (DAG). In the second experiment, the incidence of bacterial wilt, leaf gas exchange, as well as the activity of enzymes SOD, CAT, POD, PAL, PPO and phenol content were evaluated, at 0, 2, 4, 6, 8 and 15 days after inoculation with R. Solanacearum, in grafted tomato plants growing at greenhouse. In the third experiment, three grafting methods (Contact bevel, Cleft grafting and Supported grafting) and ungrafted tomato were evaluated considering the production under protected environment. The Cleft grafting method was the best for the site... (Complete abstract click electronic access below) / Doutor

The effects of petroleum mulches on the emergence and yield of tomatoes were studied at the Farmington Field Station, Greenville Field Station, North Logan, and the greenhouse. The mulches were applied as surface overlays above the seed or incorporating before plantin. Seedling emergence and yields were measured. Data recorded from trials conducted under cool weather conditions indicated that petroleum mulch overlays can be effective in increasing seedling emergence. The increased seedling emergence with petroleum mulch is due to increased soil temperature , less moisture loss from the surface, and a minimum of soil crust formation.

Plant growth, development, and environmental responsiveness are dependent on hormone-induced gene expression. This dissertation reports multiple interactions between the plant hormones auxin and ethylene and investigates their contribution to the gravitropic response, elongation growth, adventitious root formation, callus and tracheary element initiation and growth, and flower development. Four mutants of tomato (Lycopersicon esculentum, Mill.) altered in either hormone production or hormone response were used to test the involvement of ethylene and auxin. These mutants included diageotropica (dgt) which is auxin-resistant, Never-ripe (Nr), which is ethylene-resistant, epinastic (epi), which overproduces ethylene and lazy-2 (lz-2), which exhibits a phytochrome-dependent reversed-gravitropic response. Additionally, a double mutant between Nr and dgt was constructed and tested. Gravitropism was studied as an exemplary process involving both auxin and ethylene. Mutant analysis demonstrated that ethylene does not play a primary role in the gravitropic response via the currently known ethylene response pathways. However, ethylene can modify the gravitropic response, e.g. the delayed gravitropic response of the dgt mutant can be restored with exceedingly low concentrations of ethylene and ethylene synthesis- and ethylene-action inhibitors can partially inhibit the graviresponse. The role of gravity in tracheary element (TE) production was tested in microgravity (during a space shuttle flight) and in hypergravity (centrifugation). A correlation was found between gravitational force and the production of TEs, with decreased numbers of TEs produced in microgravity and increased numbers produced in response to hypergravity. Increased production of TEs by dgt in both increased and reduced gravity indicates that gravity regulates vascular development via a DGT-dependent pathway involving auxin. Combination of both the Nr and dgt mutations in a double mutant leads to plants which exhibit the reduction of auxin-sensitivity typical of dgt as well as a delay in fruit ripening typical of Nr. The reduced gravitropic response of the dgt mutant was restored to wild-type levels in the double mutant confirming a complex role for ethylene in the gravitropic response. Abnormal floral organ development was observed in a subset of double mutant flowers.These data demonstrate multiple connections between auxin and ethylene during development and provide further insight into their cellular interactions. / Graduation date: 2001

The effect of electron beam irradiation upon microbiological quality and safety of fresh-cut tomatoes was studied. Preliminary studies were conducted to ensure reliability of the rifampicin-resistant strain versus the parent strain of Salmonella serovar Montevideo for use in this study. Growth curve, heat tolerance and lactic acid resistance studies were performed, all of which showed no differences in behavior between the organisms. Fresh tomatoes were obtained from a local supplier and then cut into cubes with stem scars being separated. Both cubes and stem scars were inoculated with a rifampicin- resistant strain of either Salmonella Montevideo or Salmonella Agona, separated into treatment groups and treated by electron beam irradiation at 0.0 kGy (control), 0.7 kGy or 0.95 kGy. The effect of electron beam irradiation was determined for Salmonella, yeast, mold, and lactic acid bacteria (LAB) populations as well as pH on tomato cubes and stem scars over a 15-day storage period at 4??C. Results indicated that while irradiation treatment significantly reduced most microbial populations on tomato samples, there were no differences in the microbial populations between treatments of 0.7 kGy or 0.95 kGy. Irradiation at either dose resulted in a significant reduction of Salmonella Montevideo when compared to the control, with an initial reduction of 1.8 and 2.2 log10 CFU/g on tomatoes for 0.7 kGy and 0.95 kGy, respectively. LAB, yeasts and molds were more resistant to the treatment than Salmonella. Populations present on stem scars and tomato cubes did experience some differences in log reductions, possibly due to the protective effect of the stem scar on microorganisms. However, no differences were detected between the two Salmonella serotypes in response to irradiation treatment. This study indicates that doses of irradiation greater than 1 kGy should be used in fresh-cut tomatoes to eliminate significant populations of pathogens, as well as to ensure the microbial quality of the product. Additional studies also need to be conducted to examine the effects of higher irradiation doses on the sensory qualities of fresh-cut tomatoes.

The effect of electron beam irradiation upon microbiological quality and safety of fresh-cut tomatoes was studied. Preliminary studies were conducted to ensure reliability of the rifampicin-resistant strain versus the parent strain of Salmonella serovar Montevideo for use in this study. Growth curve, heat tolerance and lactic acid resistance studies were performed, all of which showed no differences in behavior between the organisms. Fresh tomatoes were obtained from a local supplier and then cut into cubes with stem scars being separated. Both cubes and stem scars were inoculated with a rifampicin- resistant strain of either Salmonella Montevideo or Salmonella Agona, separated into treatment groups and treated by electron beam irradiation at 0.0 kGy (control), 0.7 kGy or 0.95 kGy. The effect of electron beam irradiation was determined for Salmonella, yeast, mold, and lactic acid bacteria (LAB) populations as well as pH on tomato cubes and stem scars over a 15-day storage period at 4??C. Results indicated that while irradiation treatment significantly reduced most microbial populations on tomato samples, there were no differences in the microbial populations between treatments of 0.7 kGy or 0.95 kGy. Irradiation at either dose resulted in a significant reduction of Salmonella Montevideo when compared to the control, with an initial reduction of 1.8 and 2.2 log10 CFU/g on tomatoes for 0.7 kGy and 0.95 kGy, respectively. LAB, yeasts and molds were more resistant to the treatment than Salmonella. Populations present on stem scars and tomato cubes did experience some differences in log reductions, possibly due to the protective effect of the stem scar on microorganisms. However, no differences were detected between the two Salmonella serotypes in response to irradiation treatment. This study indicates that doses of irradiation greater than 1 kGy should be used in fresh-cut tomatoes to eliminate significant populations of pathogens, as well as to ensure the microbial quality of the product. Additional studies also need to be conducted to examine the effects of higher irradiation doses on the sensory qualities of fresh-cut tomatoes.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 160-187).

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Food Science." Includes bibliographical references.

Thesis (M.S.)--Ohio State University, 2009. / Title from first page of PDF file. Includes vita. Includes bibliographical references (p. 51-54).

Thesis (M.S.)--University of Hawaii at Manoa, 2003. / Includes bibliographical references (leaves 79-88). Also available via World Wide Web.