Made available in DSpace on 2014-06-11T19:33:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-10-06Bitstream added on 2014-06-13T20:25:32Z : No. of bitstreams: 1 souza_jo_dr_jabo.pdf: 280960 bytes, checksum: 59592e09c2bb61db6b560216e9d73b45 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Os objetivos do trabalho foram identificar raças de Bremia lactucae agente causal do míldio no período de 2006 a 2007, na região produtora de alface do Estado de São Paulo; obter linhagens de alface-crespa resistentes. Os experimentos de campo foram realizados no Setor de Olericultura e Plantas Aromático-Medicinais e no Laboratório de Melhoramento Genético de Hortaliças, do Departamento de Produção Vegetal da UNESP-FCAV, Câmpus de Jaboticabal-SP. Foram coletados 36 isolados de B. lactucae em regiões produtoras do Estado de São Paulo, que permitiram identificar três novos comportamentos do fungo, dando origem a três novas raças: SPBl:02 (63/31/19/00), SPBl:03 (63/63/19/00) e SPBl:04 (63/63/03/00). Os genes Dm-14, Dm- 17, Dm-18, Dm-36, Dm-37 e Dm-38 conferem resistência a essas novas raças identificadas. As linhagens JAB 4-2-4, JAB 4-13-7 e JAB 4-13-9 apresentaram os melhores resultados de padrão de plantas e com resistência a B. lactucae. Os genótipos ‘Amanda’, ‘Solaris’, ‘Vanda’, ‘Vera’, JAB 4-13-7 e ‘Malice’ apresentaram melhores desempenhos das características agronômicas no inverno. Para as condições de verão, JAB 4-13-7 e ‘Solaris’ apresentaram melhores desempenhos das características agronômicas. JAB 4-13-7 é o mais indicado para o cultivo de inverno pelo bom desempenho e resistência às raças de B. lactucae. ‘Malice’ apresentou o pior comportamento produtivo, apesar da resistência às quatro raças de B. lactucae avaliadas / The aims of the study were to verify the emergence of races of B. lactucae casual agent of downy mildew in the period from 2006 to 2007 in lettuce-producing region in the State of São Paulo; to obtain lines lettuce with resistance to race SPBI:01; the performance of JAB 4-13-7 before the commercials cultivars as an option to allow for the cultivation of this genotype for both evaluation periods, in the conditions of Jaboticabal and check the resistance of lettuce genotypes to four races of Bremia lactucae. The field experiments were accomplished at the Section of Vegetables Crops and Aromatic-Medicinal Plants and in the Laboratory of Vegetable Breeding of the Department of Vegetable Production from the São Paulo State University at Jaboticabal (UNESP). The monitoring of B. lactucae allowed to identify three new behaviors of the fungus, resulting in three new races SPBI:02 (63/31/19/00), SPBI:03 (63/63/19/00) SPBI:04 (63/63/03/00). The genes Dm-14, Dm-17, Dm-18, Dm-36, Dm-37 and Dm-38, confer resistance to these new identified races. The lines JAB 4-2-4, JAB 4-13-7 and JAB 4-13-9 achieved the best results of standart plants with resistance to B. lactucae. The genotypes ‘Amanda’, ‘Solaris’, ‘Vanda’, ‘Vera’, JAB 4-13-7 and ‘Malice’ showed the best performances of agronomic traits in winter. For summer conditions, JAB 4-13-7 and ‘Solaris’ presented better performances of agronomic traits. The JAB 4-13-7 is the most suitable for the winter cultivation by good performance and resistance for the races of B. lactucae. ‘Malice’ had the worst productive performance, despite the resistance to the four races of B. lactucae evaluated

Orientador: Leila Trevizan Braz / Coorientador: Tagli Dalpian / Coorientador: Margarete Camargo / Banca: Arlete Marchi Tavares de Melo / Banca: Antonio Ismael Inácio Cardoso / Banca: Modesto Barreto / Banca: Érika Auxiliadora Giacheto Scaloppi / Resumo: Os objetivos do trabalho foram identificar raças de Bremia lactucae agente causal do míldio no período de 2006 a 2007, na região produtora de alface do Estado de São Paulo; obter linhagens de alface-crespa resistentes. Os experimentos de campo foram realizados no Setor de Olericultura e Plantas Aromático-Medicinais e no Laboratório de Melhoramento Genético de Hortaliças, do Departamento de Produção Vegetal da UNESP-FCAV, Câmpus de Jaboticabal-SP. Foram coletados 36 isolados de B. lactucae em regiões produtoras do Estado de São Paulo, que permitiram identificar três novos comportamentos do fungo, dando origem a três novas raças: SPBl:02 (63/31/19/00), SPBl:03 (63/63/19/00) e SPBl:04 (63/63/03/00). Os genes Dm-14, Dm- 17, Dm-18, Dm-36, Dm-37 e Dm-38 conferem resistência a essas novas raças identificadas. As linhagens JAB 4-2-4, JAB 4-13-7 e JAB 4-13-9 apresentaram os melhores resultados de padrão de plantas e com resistência a B. lactucae. Os genótipos 'Amanda', 'Solaris', 'Vanda', 'Vera', JAB 4-13-7 e 'Malice' apresentaram melhores desempenhos das características agronômicas no inverno. Para as condições de verão, JAB 4-13-7 e 'Solaris' apresentaram melhores desempenhos das características agronômicas. JAB 4-13-7 é o mais indicado para o cultivo de inverno pelo bom desempenho e resistência às raças de B. lactucae. 'Malice' apresentou o pior comportamento produtivo, apesar da resistência às quatro raças de B. lactucae avaliadas / Abstract: The aims of the study were to verify the emergence of races of B. lactucae casual agent of downy mildew in the period from 2006 to 2007 in lettuce-producing region in the State of São Paulo; to obtain lines lettuce with resistance to race SPBI:01; the performance of JAB 4-13-7 before the commercials cultivars as an option to allow for the cultivation of this genotype for both evaluation periods, in the conditions of Jaboticabal and check the resistance of lettuce genotypes to four races of Bremia lactucae. The field experiments were accomplished at the Section of Vegetables Crops and Aromatic-Medicinal Plants and in the Laboratory of Vegetable Breeding of the Department of Vegetable Production from the São Paulo State University at Jaboticabal (UNESP). The monitoring of B. lactucae allowed to identify three new behaviors of the fungus, resulting in three new races SPBI:02 (63/31/19/00), SPBI:03 (63/63/19/00) SPBI:04 (63/63/03/00). The genes Dm-14, Dm-17, Dm-18, Dm-36, Dm-37 and Dm-38, confer resistance to these new identified races. The lines JAB 4-2-4, JAB 4-13-7 and JAB 4-13-9 achieved the best results of standart plants with resistance to B. lactucae. The genotypes 'Amanda', 'Solaris', 'Vanda', 'Vera', JAB 4-13-7 and 'Malice' showed the best performances of agronomic traits in winter. For summer conditions, JAB 4-13-7 and 'Solaris' presented better performances of agronomic traits. The JAB 4-13-7 is the most suitable for the winter cultivation by good performance and resistance for the races of B. lactucae. 'Malice' had the worst productive performance, despite the resistance to the four races of B. lactucae evaluated / Doutor

Resumo: A água vem se tornando um recurso cada vez mais escasso, sendo necessário utilizá-la com maior cautela. Sabe-se que a agricultura é a atividade que mais consome água, deve-se então encontrar formas de minimizar a utilização na irrigação de água própria para o consumo humano. Sendo a agricultura uma atividade em que se pode utilizar águas de qualidade inferior, sem comprometer a cultura, o reuso de água surge como uma alternativa para reduzir o consumo de água de boa qualidade. Porém, faz-se necessário determinar se a reutilização de água é um método seguro ambientalmente, além de garantir que a produção seja satisfatória e sem ocorrência de contaminação da cultura. Assim, o presente trabalho teve como objetivo verificar o potencial de contaminação das águas subterrâneas por nitrogênio devido à irrigação com efluente do tratamento de esgoto, bem como, avaliar o cultivo da cultura da alface e a ocorrência de contaminação microbiológica na mesma. Para tanto, foram determinadas as concentrações das formas de nitrogênio presentes no percolado de área irrigada com água residuária, bem como, os parâmetros de crescimento e contaminação da alface por Salmonella. Observou-se, no percolado de área irrigada com água residuária, concentrações de nitrato de 33,14 a 47,97 mg.L-1 a 25 cm de profundidade e de 17,73 a 141,9 mg.L-1 a 50 cm de profundidade. Já as concentrações de nitrito e amônia foram inferiores, com o nitrito apresentando, a 25 cm de profundidade, concentrações de 0,0083 a 0,0301 mg.L-1 e a 50 cm as concentrações ficaram entre 0,0059 a 0,0119 mg.l-1. Para a amônia as concentrações ficaram entre 0,215 e 0,527 mg.L-1 a 25 cm de profundidade e a 50 cm de profundidade as concentrações foram de 0,279 a 0,814 mg.L-1. Também se verificou que os... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The water is becoming a scarce resource, being necessary to use it with more caution. It is known that agriculture is the activity that consumes more water, so is needed to find ways of minimize the use in irrigation of water adequated to human consumption. The agriculture is an activity that can receive water of lower quality, with no compromise of the culture, so the water reuse is an alternative to reduce the use of water with better quality. However, it is necessary to determine if the water reuse is environmentally safe and if it guarantees satisfactory production with no contamination of the culture. Thus, the present work aimed to verify the potential of contamination of groundwater by nitrogen due to irrigation with effluent of sewage treatment, and also, evaluate the lettuce grouth and microbiological contamination. So, it was determined the concentrations of nitrogen forms present in the leachate from area irrigated with wastewater, as well as the growth parameters and contamination of lettuce by Salmonella. It was observed in the leachate from area irrigated with wastewater, concentrations of nitrate from 33,14 to 47,97 mg.L-1 at 25 cm deep, and 17,73 to 141,9 mg.L-1 at 50 cm deep. But the nitrite and ammonia concentrations were lower, with nitrite presenting, at 25 cm deep, concentration of ,0083 to 0,0301 mg.L-1, and at 50 cm the concentrations were from ,0083 to 0,0301 mg.L-1. To ammonia the concentration were between 0,215 and 0,527 mg.L-1 at 25 cm deep and at 50 cm deep the concentrations were from 0,279 to 0,814 mg.L-1. It was verified that the parameters of crop growth were higher for the irrigation with wastewater, besides, there were no microbiological contamination of the lettuce, being in accordance with the legislation of vegetables / Orientador: Raimundo Leite Cruz / Coorientador: Elisandro Pires Frigo / Banca: Antonio Evaldo Klar / Banca: Alessandra Monteiro de Paula / Mestre

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Although it had been early developed aiming to search on the plants mineral nutrition, the hydroponic gained more importance between the growers due to possibility a better nutritional control that confers greater plant quality and minor incidence of pests. Some hydroponic systems have been considered for the lettuce grown, between them NFT (Nutrient Film Technique) and Floating System. This last one consists of the use of great amounts of nutrient solution in tanks where the plants are floating on plates with its roots flooded. This system has been showing promising for hot climates where the high temperatures can to limit the growing in other systems as the NFT. Therefore, a trial was carried out to evaluate the floating system in its diverse characteristics as stability of the electrical conductivity and pH, availability of dissolved oxygen to the plants and temperature of the nutrient solution. Also was evaluated, through the total fresh weight and root length, the cultivars VerÃnica and Vera, which are spread out between the growers that use hydroponic systems, in regards to its adaptability to the floating system. Each one of the cultivars were submitted at two levels of electrical conductivity (1,5mS/cm and 2,5 mS/cm) and two levels of artificial aeration (20min/h and 60min/h) in split-split-plot design. The study showed that the cultivar Vera was significantly better than VerÃnica concerning to the total fresh weight and root length. It did not have significant difference between the studied levels of electrical conductivity and artificial aeration in the development of the plants. It could still be observed that the system revealed sufficiently steady in regards to the evaluated parameters. / Embora tenha sido desenvolvida primeiramente com o objetivo de pesquisar sobre a nutriÃÃo mineral das plantas, a hidroponia ganhou bastante importÃncia entre os produtores devido à possibilidade do controle nutricional mais estreito que confere maior qualidade Ãs plantas e menor incidÃncia de problemas fitossanitÃrios. VÃrios sistemas hidropÃnicos tÃm sido propostos para o cultivo de alface, entre eles o NFT (Nutrient Film Technique) e o sistema de leito flutuante (Floating System). Este Ãltimo consiste da utilizaÃÃo de grandes quantidades de soluÃÃo nutritiva dispostas em tanques onde as plantas ficam flutuando sobre placas de material leve com suas raÃzes imersas. Este sistema tem se mostrado promissor para climas quentes onde as altas temperaturas podem ser limitantes ao cultivo em outros sistemas como o NFT. Diante do exposto foi realizado trabalho no sentido de avaliar o sistema de leito flutuante em suas diversas caracterÃstica como estabilidade da condutividade elÃtrica e pH, disponibilidade de oxigÃnio dissolvido Ãs plantas e temperatura da soluÃÃo nutritiva. TambÃm foram avaliadas, atravÃs da matÃria fresca total e comprimento radicular, os cultivares VerÃnica e Vera, os quais sÃo os mais difundidos entre os produtores que utilizam o sistema hidropÃnico, quanto à sua adaptabilidade ao sistema de leito flutuante. Para isso cada cultivar foi submetido a dois nÃveis de condutividade elÃtrica (1,5mS/cm e 2,5 mS/cm) e dois nÃveis de aeraÃÃo artificial (20min/h e 60min/h) utilizando o delineamento em parcelas subsubdivididas. O estudo mostrou que o cultivar Vera foi significativamente superior ao VerÃnica em relaÃÃo à matÃria fresca total e comprimento radicular. NÃo houve diferenÃa significativa entre os nÃveis de condutividade elÃtrica e aeraÃÃo artificial estudados no desenvolvimento das plantas. PÃde-se observar ainda que o sistema mostrou-se bastante estÃvel em relaÃÃo Ãs variÃveis avaliadas.

Diante da previsão de escassez de água no mundo, torna-se necessário desenvolver tecnologias que permitem o reaproveitamento de águas salinas.A hidroponia é uma técnica de cultivo sem solo que permite obter produtos de alta qualidade, maior produção por área, menor gasto de água e insumos agrícolas, contribuindo com a preservação dos recursos naturais e do ambiente. A alface (Lactuca sativa) é a hortaliça mais importante produzida no sistema hidropônico (NFT). O uso de água salina na produção de hortaliças constitui no momento atividade essencial, tendo em vista o aumento da demanda de água doce, tanto pela atividade agrícola quanto pelo abastecimento urbano e industrial. Dessa forma os objetivos do trabalho são: i) avaliar o crescimento, a produção e qualidade de duas variedades cultivadas de alface (Verônica e Pira Roxa) em sistema hidropônico NFT (Fluxo Laminar de Nutrientes) com a utilização de águas salinas no preparo da solução nutritiva e na reposição da lâmina diária evapotranspirada ao longo do ciclo de cultivo; ii) avaliar a qualidade, os parâmetros fisiológicos e bioquímicos (teor de nitrato, clorofila e prolina). Os experimentos foram conduzidos em ambiente protegido localizado na área experimental do Setor de Irrigação e Drenagem do Departamento de Engenharia Rural da Escola Superior de Agricultura Luiz de Queiroz - ESALQ/USP, no município de Piracicaba-SP. O delineamento experimental foi blocos ao acaso. Avaliaram-se cinco níveis de salinidade obtidos com a adição de NaCl, que resultaram em diferentes condutividades elétricas da água: 0,42, 1,53, 3,52, 5,55 e 7,43 (dS.m-1) e duas variedades cultivadas de alface Verônica e Pira Roxa. Os resultados revelaram que a salinidade da água reduziu o crescimento e a produção de forma linear decrescente. A tolerância à salinidade de alface variedade cultivada Verônica foi superior em relação à variedade cultivada Pira Roxa. A salinidade alterou o teor de nitrato, prolina e clorofila, sendo o efeito superior na cv. Pira Roxa, denotando ser um mecanismo de defesa à salinidade. Com relação à produtividade comercial, obteve-se uma perda de 69% e 64% para as variedades cultivadas Pira Roxa e Verônica, respectivamente, quando se utilizou água mais salina (7,43 dS.m-1). Os resultados obtidos em sistema de cultivo NFT podem indicar a possibilidade do uso da água salina como alternativa para produção de hortaliças para produtores que tem disponibilidade de água salina e restrita disponibilidade de água doce. / Before the forescast of shortage of water in the world, becomes necessary to develop technologies that allow the reuse of saline waters. The NFT (Nutrient Film Technique) is a cultivation technique soil less that allows to obtain products of high quality, larger production for area, minor expense of water and agricultural inputs, contributing with the preservation of the natural resources and environment. A lettuce (Lactuca sativa) is the most important vegetable produced in the hydroponic system (NFT). The use of saline water in the production of vegetables constitutes in the moment essential activity, tends in view the increase of the demand of fresh water, so much for the agricultural activity as for the urban and industrial supplying. The objectives of the work were: i) to evaluate the growth, the production and quality of two cultivates of lettuce (Verônica and Pira Roxa) cultivated in hydroponic system NFT (Nutrient Film Technique) with the use of saline waters in the preparation of the nutrient solution and replacement of the evapotranspiration along the cultivation cycle; ii) to evaluate quality, the physiologic and biochemical parameters (nitrate, chlorophyll and prolina content). The experiments were carried out in atmosphere protected on the experimental area of the Irrigation and Drainage Section of the University of São Paulo (ESALQ/USP), Piracicaba, State of São Paulo, Brazil. The experimental design used was randomized blocks. It were evaluated five salinity levels obtained with the addition of NaCl that resulted in different electrical conductivities of the water (0.42, 1.53, 3.52, 5.55 and 7.43 dS.m-1); and two cultivated variety of lettuce Verônica and Pira Roxa. The results revealed that the salinity of the water reduced the growth and production in a decreasing lineal. The tolerance to salinity of the lettuce cultivated variety Verônica was superior in relation cultivated variety Pira Roxa. The salinity altered the contents of nitrate, prolina and chlorophyll, being the superior effect in the cv. Pira Roxa, denoting to be a defense mechanism the salinity. The commercial productivity was obtained a loss of 69% and 64% for cultivated variety Pira Roxa and Verônica, respectively, when more saline water was used (7,43 dS.m-1). The results obtained in cultivation system NFT they can indicate the possibility of the use of the saline water as alternative for production of vegetables for producers that has availability of saline water and restricted of fresh water.

Master of Science / Food Science Institute / Sara E. Gragg / Leafy greens have been recognized as vehicles for transmission of foodborne pathogens and an effective pre-harvest intervention to control them is currently lacking. After harvest, lettuce is often subjected to chlorinated water to reduce the microbial load in the water and on the lettuce tissue. While moderately effective, there is also a need for improved postharvest interventions. The purpose of Objective I was to 1) determine potassium bisulfate efficacy at reducing populations of Escherichia coli (E. coli) and Listeria innocua (L. innocua) when applied pre-harvest to lettuce, and 2) assess the impact on product quality at harvest. Potassium bisulfate reduced E. coli populations on inoculated lettuce by 1.32 log₁₀ CFU/g (P=0.0002) and L. innocua by 1.18 log₁₀ CFU/g (P=0.0017). No detectable differences were observed in color (P>0.05); however, brown spots were observed on various leaves sprayed with potassium bisulfate. The purpose of Objective II was to employ a blend of benzalkonium chloride, acetic acid, and methyl paraben (BAM) as a postharvest wash on romaine and iceberg lettuce and to 1) determine efficacy at reducing populations of Listeria monocytogenes (L. monocytogenes), E. coli O157:H7 and Salmonella, 2) measure changes in aerobic bacteria throughout the shelf life, and 3) quantify benzalkonium chloride and methyl paraben residues post-washing. To quantify efficacy of BAM reducing pathogenic bacterial populations, fresh-cut romaine and iceberg lettuce were inoculated with L. monocytogenes, E. coli O157:H7, or Salmonella and washed in BAM at concentrations of 0%, 1%, 2% or 3% for one or five minutes. When plated on recovery media, contact time and wash concentration was not significant (P>0.05) for Salmonella on either product. Concentration was significant (P=0.0189) for L. monocytogenes on romaine; however, the greatest reduction observed was <1.0 log₁₀ CFU/g. The 3% wash significantly reduced E. coli O157:H7 on romaine by 1.75 log₁₀ CFU/g, which is 0.66 log₁₀ CFU/g better than the 0% wash. Following washing, wash water was analyzed and data demonstrate that all wash concentrations significantly (P≤0.05) reduced each foodborne pathogen by >2.0 log₁₀ CFU/g in the wash water. To quantify benzalkonium chloride and methyl paraben residues, as well as changes in aerobic bacteria and product quality, fresh-cut romaine and iceberg lettuce were subjected to a 1 minute wash in BAM at concentrations of 0%, 1%, 2%, or 3% and immediately sampled to determine aerobic populations and product quality. Concentrations 0% and 2% were also packaged into retail storage bags and sampled on days 0, 3, 5, and 7. Residues were quantified on these days as well. On day 0, aerobic populations did not vary according to wash concentration (P>0.05). With regards to shelf-life data, the 2% wash significantly reduced (P=0.0203) aerobic bacteria on romaine lettuce; however, no significant difference was observed on iceberg lettuce (P=0.0819). With regards to overall visual appearance of romaine or iceberg lettuce, no significant difference was detected between 0% and 2% BAM washes for each day throughout the shelf-life study (P>0.05). Methyl paraben and benzalkonium chloride residues were <5.0 and <10.0 ppm, respectively, on both products on each sampling day.

A deteriorating trend has been noted in the bacteriological quality of surface irrigation water sources in South Africa. In a bid to compare the bacteriological quality of two irrigation water sources as well as whether irrigation water was a source of bacterial pathogens on irrigated lettuce, this study was designed and divided into two phases. Phase one involved determination of physico-chemical parameters and bacterial indicators in the Loskop canal, the Skeerpoort river and lettuce irrigated with water from the Skeerpoort river over 10 months. Co-currently the study further determined the diversity of the most prevalent bacterial microflora in the 3 sample sources over the same time period. Aerobic colony counts (ACC), Aerobic spore formers (ASF), Anaerobic spore formers (AnSF), Faecal coliforms (FC), Intestinal enterococci (IE) and Staphylococcus aureus (S. aureus) as well as prevalence of Escherichia coli (E. coli), Salmonella spp and Listeria monocytogenes (L. monocytogenes) were determined. Additionally the most prevalent aerobic bacterial species isolated from the three sources were determined. Higher mean rainfall was noted in areas surrounding the Skeerpoort river (74.7mm) than the Loskop canal (0.1mm). Mean temperature was 15.4˚C and 18.2˚C while mean pH was 7.4 and 8.4 in the Loskop canal and the Skeerpoort river respectively. Low mean bacterial counts of less than 3.4 log10cfu/ml, were noted for ACC, ASF, AnSF, S. aureus and IE at both irrigation sites. Higher mean ACC of 5.9 log10cfu/g and S. aureus counts of 3.0 log10cfu/g were noted on lettuce. Although low mean counts of FC (1.3 log10cfu/100ml) were noted for all three sources, high incidence of E. coli was observed during bacterial composition studies on nonselective media. This suggested underestimation of faecal contamination possibly indicating that identification of specific pathogens provided a better measure of assessing bacterial contamination than bacterial indicators. E. coli, Bacillus spp and Enterobacter spp were the most prevalent bacteria in the Loskop canal, the Skeerpoort river and on lettuce. Prevalence of E. coli, Bacillus spp and Enterobacter spp in the Loskop canal was 23%, 33% and 26% respectively. Similarly prevalence in the Skeerpoort river was 36%, 26%, 16% respectively. On lettuce prevalence of the same bacteria was 36%, 30% and 6% respectively. E. coli O157:H7 was isolated at both irrigation sites while Salmonella enterica (gp 1) ST paratyphi A was isolated from the Skeerpoort river. High prevalence of similar bacterial species within the Loskop canal and the Skeerpoort river suggested similar sources of contamination in the two water sources inspite of different geographical location and surrounding land use practices. Additionally, similar bacterial species in irrigation water from the Skeerpoort river and on irrigated lettuce suggested water as a source of contamination on produce. Additionally it suggests ability of bacterial pathogens to withstand environmental conditions under field conditions which may pose a risk to food safety and public health among individuals consuming irrigated fresh produce. Phase 2 aimed at determining the prevalence of antibiotic resistant and virulent E. coli collected from the Loskop canal, the Skeerpoort river and lettuce irrigated with water from the Skeerpoort river. Forty one (41) E. coli isolates: (19) Loskop canal; (12) the Skeerpoort river; (10) lettuce were tested with 11 antibiotics at single concentrations and screened for Shigatoxin 1 (stx 1), Shigatoxin 2 (stx 2) and intimin (eae) genes. Antibiotic resistance was also used as a means of clustering E. coli isolated from the 3 sources. In the Loskop canal 84% and 83% of strains in the Skeerpoort river were resistant to at least one antibiotic. There was a significant difference (p≤0.05) in resistance to antibiotics between isolates from the Loskop canal and the Skeerpoort river. Additionally the combined effect of isolate source (irrigation water site) and antibiotics for isolates from the Skeerpoort river was significant (p≤0.05). From lettuce, 90% of isolates were resistant to at least one antibiotic and resistance significantly differed (p≤0.05) from isolates in the Skeerpoort river. The highest resistance to single antibiotics in all three samples was to cephalothin and ampicillin. Higher resistance was noted to multiple (more than 2) antibiotics in the Skeerpoort river (33%) than Loskop canal (5%). Most isolates from the same source showed close relatedness. Close relatedness was noted between isolates from the Loksop canal (10.5%) and the Skeerpoort river (16%). From irrigated lettuce 40% of isolates showed close relatedness to isolates in irrigation water from the Skeerpoort river. In the Loskop canal 15% and 41% of isolates in the Skeerpoort river possessed virulence genes. From lettuce, 20% of isolates possessed virulence genes. In the Loskop canal as well as from lettuce all isolates with virulence genes were antibiotic resistant while 80% of isolates with virulence genes in the Skeerpoort river were antibiotic resistant. In the Loskop canal 10% and 25% of isolates in the Skeerpoort river were positive for stx1/stx2 and eae, genes synonymous with Enterohaemorrhagic E. coli (EHEC). Results from this study show that E. coli from the two irrigation water sources as well as on irrigated lettuce were resistant to antibiotics and potentially pathogenic. This may increase risk of contaminating irrigated fresh produce which may compromise food safety and public health of consumers. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Food Science / unrestricted

Lettuce (Lactuca sativa L.) seedlings diseases caused by soilborne pathogens are characterised by root rot, stem rot and damping-off of the seedlings that can occur at any time during growth. Fusarium solani, Pythium ultimum and Rhizoctonia solani are known to be the important destructive pathogens of lettuce, causing severe yield losses in South Africa. The aim of this research was to evaluate the effects of three selected fungicides to control these pathogens on lettuce seedlings. In this study the fungicides metalaxyl (Apron®), fludioxonil (Celest®) and mefenoxam (Subdue®) were applied at two concentrations as single and double doses on lettuce seedlings to determine their efficacy to control the pathogens Fusarium solani, Pythium ultimum and Rhizoctonia solani after significant reduction of mycelia growth was observed in vitro. Cultures of P. ultimum (UPGH024), R. solani (UPGH122) and F. solani (UPGH122) were obtained from the culture collection of the Department of Microbiology and Plant Pathology, University of Pretoria and cultivated on PDA for 2 days at 25ºC. Pasteurised soil was artificially inoculated with these pathogens. For the first experiment lettuce seeds were planted in polystyrene seedling trays at a depth of 1.0 cm. There were four replications of 50 seeds per treatment. In Experiment 2 pots (12 cm x 7 cm) were filled with pasteurised growing medium and 3-week old seedlings were transplanted. There were three replications of six pots containing three plants each. Seedling trays and pots were drenched with fungicides and placed in a randomised block design in a controlled environment room at 20- 26°C with a 12h-light/dark regime. The seedling trays and pots were rotated daily in the room. Seedling trays and pots were watered daily to maintain field capacity. The seedlings were able to grow larger in the pots than in seedling trays. It was confirmed that the treatment with fludioxonil (Celest®) at double and single dose inhibited the growth of the three fungi F. solani, P. ultimum and R. solani on lettuce seedlings without causing phytotoxicity. All three fungicides significantly reduced the diseases caused by the three pathogens. These findings are consistent with previous reports that fludioxonil, metalaxyl and mefenoxam can control oomycete fungi. There are few registered fungicides for the control of Fusarium solani, Pythium ultimum and Rhizoctonia solani on lettuce, therefore further work will aim to confirm these results in the field. / Dissertation (MInstAgrar)--University of Pretoria, 2008. / Microbiology and Plant Pathology / unrestricted

Lettuce heads (Cultivar "Great Lakes") were stored in different concentrations of O2 and CO2, including l percent O2 and l percent CO2, 2.5 percent O2 and 2.5 percent CO2, 5 percent O2 and 0 percent CO2, and 5 percent O2 and 5 percent CO2; temperatures of 35 and 70 F; and with or without microbe- and senescence-inhibiting chemicals and packaging. The samples were taken on the twentieth and fortieth days in the first series of experiments; and in the subsequent experiments, on the fifteenth, thirtieth, forty-fifth, sixtieth, and seventy-fifth days of storage for quality evaluation, determination of rate of respiration, and chemical analyses. The results indicated that lettuce could be stored at 35 F for at least 2 to 3 weeks. At this temperature, lettuce heads were still field fresh and bright green, without apparent sign of quality deterioration. At 70 F, none of the treatments could prolong the shelf-life of the lettuce more than l week. Lettuce heads maintained the best marketing quality when stored in atmospheres of 2.5 percent O2 and 2.5 percent CO2 at 35 F for 60 days. Microbe- and senescence-inhibiting chemicals (Captan, Phaltan, Mycostatin, and N6-benzyladenine) had detrimental effects on the quality of lettuce stored in controlled atmosphere. The reduction in russet spotting was the major benefit in controlled atmosphere storage at 35 F. In addition, the incidence of pink rib and butt discoloration was less than for those lettuce heads held in the conventional refrigerator. However, the hearts of the lettuce were sensitive to low O2 injury in controlled atmospheres consisting of 1 percent O2 and l percent CO2. Controlled atmosphere (2.5 percent O2, 2.5 percent CO2) and controlled atmosphere combined with polyethylene packaging reduced the CO2 production, degradation of chlorophyll, loss of total sugar, and starch. Phaltan (microbe inhibitor, 1,000 ppm) or Phaltan in combination with polyethylene packaging under controlled atmosphere storage had an adverse effect on the lettuce held in the conventional refrigerator. In every case, the rate of respiration was in direct correlation with the sugar retention data.

No description available.