Orientador: Ben-Hur Mattiuz / Coorientador: Arthur Bernardes Cecílio Filho / Banca: Bianca Sarzi de Souza / Banca: Luis Felipe Purquerio / Banca: José Fernando Durigan / Banca: Teresinha de Jesus Deléo Rodrigues / Resumo: Este trabalho teve por objetivo verificar a aplicação de silício em hidroponia e na influencia na produção e na conservação pós-colheita de alface americana cv. Lucy Brown, em ambiente refrigerado e minimamente processado. No primeiro experimento foi realizada sua produção hidropônica com doses crescentes de silício (0; 28; 56 e 84 mg L-1) utilizando como fonte silicato de potássio, e avaliadas quanto à massa fresca, massa seca, teor de silício e de macronutrientes. No segundo experimento, alfaces produzidas em hidroponia com silício (condições do primeiro experimento) foram armazenadas a 8 °C, 80±3%UR e 22 °C, 80±3%UR, e avaliadas quanto, perda de massa fresca, firmeza, aos teores de clorofila, sólidos solúveis e de acidez titulável, pH, atividade das enzimas peroxidase, polifenoloxidase e fenilalanina amônia-liase. No terceiro experimento, após a produção hidropônica, as alfaces foram submetidas ao processamento mínimo, embaladas, armazenadas a 3 °C, 85±3% UR e avaliadas a cada quatro dias quanto aos teores de O2 e CO2 nas embalagens, sólidos solúveis, e acidez titulável, e clorofila, firmeza e atividade das enzimas peroxidase e polifenoloxidase. A concentração de 84 mg L-1 de Si proporcionou maior absorção de silício e massa fresca para as alfaces. As folhas velhas apresentaram maior teor de silício quando comparada com as folhas novas. A associação da dose de 84 mg L-1 de Si com a temperatura de 8 ºC propiciaram maior firmeza das folhas, menor perda de massa fresca e baixa atividade das enzimas polifenoloxidase e peroxidase durante o período. A concentração de 84 mg L-1 de silício aumentou a firmeza das folhas e manteve constante os teores de clorofila nas alfaces minimamente processadas conservando sua vida útil por 16 dias / Abstract: This study aimed to verify the application of silicon in hydroponics and influence the production and postharvest of lettuce cv. Lucy Brown in refrigerated environment and minimally processed. The first experiment was conducted hydroponic production with increasing concentration of silicon (0, 28, 56 and 84 mg L- 1) using as source of potassium silicate, and assessed for fresh weight, dry weight, silicon and macronutrients content. In the second experiment, lettuce grown in hydroponics with silicon (conditions of the first experiment) were stored at 8 °C, 80 ± 3% RH and 22°C, 80 ± 3% RH, and evaluated, weight loss, firmness, chlorophyll, soluble solids and titratable acidity contents , pH, activity of peroxidase, polyphenoloxidase and phenylalanine ammonia lyase. In the third experiment, after producing hydroponic lettuce were subjected to minimal processing, packaged, stored at 3 °C, 85 ± 3% RH and evaluated every four days for the levels of O2 and CO2 in packaging, soluble solids, and titratable acidity, and chlorophyll, firmness and activity of peroxidase and polyphenoloxidase. The concentration of 84 mg L-1 of Si provided greater absorption of silicon and fresh weight for lettuce. Old leaves had higher silicon content compared to new leaves. The association of the dose of 84 mg L-1 of Si with temperature of 8 °C promoted greater firmness of leaves, lower weight loss and low activity of polyphenoloxidase and peroxidase enzymes during the period. The concentration of 84 mg L-1 silicon increased firmness of the leaves and kept constant the concentration of chlorophyll in minimally processed lettuce conserving its life for 16 days / Doutor

Orientador: Dirceu Maximino Fernandes / Banca: Hélio Grassi Filho / Banca: Giuseppina Pace Pereira Lima / Banca : Jacob Silva Souto / Banca: Anelisa de Aquino Vidal / Resumo: O silício é considerado como elemento benéfico para as plantas, possuindo papel de resistência às plantas que tem sido particularmente atribuído à modificação nas propriedades da parede celular trazendo benefícios contra a ação deletéria do alumínio. Dois experimentos foram realizados com o objetivo de verificar o possível efeito de doses crescentes de silício contra a ação deletéria do Al3+ em duas cultivares de milho modificando o tempo de exposição das raízes em solução nutritiva contendo Si. Os experimentos foram conduzidos em casa de vegetação no Departamento de Recursos Naturais/ Área Ciência do Solo, FCA/UNESP, Botucatu-SP, utilizando vasos de plástico com capacidade de 4,5 litros de solução. O delineamento experimental utilizado foi o de blocos casualizados com três repetições, constituindo-se de um fatorial 4x2, com quatro doses (0, 1, 2 e 4 mmol L-1 de Si) e as variedades, Exceler - sensível e AG8060 - tolerante ao Al3+. Após cada período de contato com Si o Al3+ foi adicionado em solução permanecendo por dez dias. Os seguintes parâmetros foram avaliados: comprimento no período inicial e final, massa fresca e seca, teor e acúmulo dos nutrientes, Si e fenóis solúveis totais da raiz e parte aérea das duas cultivares de milho. A cultivar Exceler em contato com Al3+ em solução apresentou menor desenvolvimento radicular quando comparada com a cultivar AG8060 mesmo sob influência do Si. A maior massa fresca e seca na raiz foi encontrada na cultivar AG8060 e a maior massa fresca e seca na parte aérea foi encontrada na cultivar Exceler, mesmo sendo sensível ao Al3+. O teor e acúmulo de Si na raiz foi maior na cultivar Exceler mostrando ser mais eficiente na absorção desse elemento. Quando as plantas ficaram maior tempo em contato com Si em solução no primeiro... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Silicon is considered as a beneficial element for plants. It has a great role in plants particularly attributed to changes in the properties of the cell wall bringing benefits against the deleterious action of aluminum. Two experiments were carried out with the aim to verify the possible effects of increasing doses of silicon against the deleterious action of Al3+ in two cultivars of corn. It was changed the root exposure time in nutritive solution containing Si. The experiments were carried out in a greenhouse of Department of Natural Resources - Soil Science, School of Agronomical Sciences - FCA/UNESP, located in Botucatu-SP. Were utilized plastic vessels with 4,5 liters of solution. The experimental design was in a randomized blocks with three replications. It was taken a 4x2 factorial, with four doses (0, 1, 2 and 4 mmol L-1 Si) and two varieties of corn - sensitive and tolerant to Al3+. After ending each period of contact with Si, it was added the Al3+ in solution, remaining for 10 days. Were evaluated the following parameters: length of plants at the initial and end periods, fresh and dry matter, content and accumulate of essential nutrients and Si and total soluble phenols in root and aerial part of both cultivars of corn. Exceler cultivar in the presence of Al3+ in solution presented less root development when compared to AG8060 cultivar even under influence of Si. The highest fresh and dry matter in roots was noted in AG8060 cultivar, and the highest fresh and dry matter in aerial part was noted in Exceler cultivar even... (Complete abstract click electronic access below) / Doutor

Orientador: Marineide Rosa Vieira / Banca: Liliane Santos de Camargos / Banca: Luciana Cláudia Toscano Maruyama / Resumo: O ácaro-rajado, Tetranychus urticae Koch, é uma das principais pragas da cultura do mamoeiro e seu principal método de controle é o químico, como método alternativo, tem sido pesquisada a indução de resistência da planta hospedeira, a qual envolve a ativação de mecanismos de defesa existentes nas plantas. Essa estratégia de controle apresenta potencial para o uso no manejo integrado de pragas e o silício é uma das possibilidades a ser usada. Assim, o objetivo do trabalho foi determinar se a aplicação de silicato de potássio em plantas de mamoeiro pode afetar o desenvolvimento populacional do ácaro-rajado, T. urticae, e diminuir a sua infestação. No primeiro experimento, o experimento foi delineado em blocos casualizados com seis tratamentos e oito repetições, sendo cada repetição constituída por uma planta de mamoeiro infestada artificialmente com fêmeas de T. urticae provenientes de criação de laboratório. Foram testadas doses de silicato de potássio, via foliar: T1 - testemunha; T2 - 2 L ha -1 com 3 pulverizações; T3 - 2 L ha -1 - 2 pulverizações; T4 - 4 L ha -1 - 3 pulverizações; T5 - 4 L ha -1 - 2 pulverizações; T6 - 4 L ha -1 - 1 pulverização. Foram realizadas três avaliações, contando-se o número de ovos, ácaros e exúvias de T. urticae presentes ao longo da nervura principal de uma folha infestada por parcela. No segundo experimento, em casa de vegetação, o experimento foi delineado em blocos casualizados com quatro tratamentos e oito repetições, sendo cada repetição constituída por uma planta de mamoeiro infestada artificialmente com fêmeas de T. urticae provenientes de criação de laboratório. Foram testadas doses de silicato de potássio, via solo e foliar: T1 - testemunha; T2 - 4 L ha -1 via foliar com 4 pulverizações; T3 - 4 L ha -1 via foliar com 9 pulverizações e T4 - 8 L ha -1 via solo com 7 aplicações. Foram realizadas quatro avaliações,... / Abstract: The twospotted spider mite, Tetranychus urticae Koch, it is a principal pest of papaya crop and its main control method is the chemical, as an alternative method has been researched host plant resistance induction, which involves the activation of mechanisms defense of existing plants. This control strategy has potential for use in integrated pest management and silicon is one of the possibilities to use. The objective of the work was to determine whether potassium silicate application on papaya plants induces resistance to the twospotted spider mite, T. urticae, and decreases its infestation. In the first experiment, the experiment was designed in randomized blocks with six treatments and eight repetitions, with each repetition consists of a papaya plant artificially infested with T. urticae females from laboratory creation. Doses of potassium silicate were tested, foliar: T1 - control; T2 - 2 L ha -1 - 3 sprays; T3 - 2 L ha -1 - 2 sprays; T4 - 4 L ha -1 - 3 sprays; T5 - 4 L ha -1 - 2 sprays; T6 - 4 L ha -1 - 1 spray. Three evaluations were carried out by counting the number of eggs, mites and exuviae of T. urticae present along the main vein of a leaf infested by installment. In the second experiment, in the greenhouse, the experiment was designed in randomized blocks with four treatments and eight repetitions, each repetition consisting of one papaya plant artificially infested with T. urticae females from laboratory creation. Doses of potassium silicate were tested, on soil and sprayed on leaves: T1 - control; T2 - 4 L ha -1 with 4 foliar sprays; T3 - 4 L ha -1 with 9 foliar sprays and T4 - 8 L ha -1 in the soil with 7 applications. Four evaluations were carried out by counting the number of eggs, mites and exuviae of T. urticae present along the main vein of a leaf infested by installment. In laboratory, were built fertility life tables of T. urticae fed papaya leaves the plants of receiving application of ... / Mestre

Made available in DSpace on 2014-06-11T19:30:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-02-24Bitstream added on 2014-06-13T19:19:13Z : No. of bitstreams: 1 costa_lrt_dr_botfca.pdf: 954077 bytes, checksum: c4d1c0596598e88dfaff3cff43346842 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O silício é considerado como elemento benéfico para as plantas, possuindo papel de resistência às plantas que tem sido particularmente atribuído à modificação nas propriedades da parede celular trazendo benefícios contra a ação deletéria do alumínio. Dois experimentos foram realizados com o objetivo de verificar o possível efeito de doses crescentes de silício contra a ação deletéria do Al3+ em duas cultivares de milho modificando o tempo de exposição das raízes em solução nutritiva contendo Si. Os experimentos foram conduzidos em casa de vegetação no Departamento de Recursos Naturais/ Área Ciência do Solo, FCA/UNESP, Botucatu-SP, utilizando vasos de plástico com capacidade de 4,5 litros de solução. O delineamento experimental utilizado foi o de blocos casualizados com três repetições, constituindo-se de um fatorial 4x2, com quatro doses (0, 1, 2 e 4 mmol L-1 de Si) e as variedades, Exceler - sensível e AG8060 – tolerante ao Al3+. Após cada período de contato com Si o Al3+ foi adicionado em solução permanecendo por dez dias. Os seguintes parâmetros foram avaliados: comprimento no período inicial e final, massa fresca e seca, teor e acúmulo dos nutrientes, Si e fenóis solúveis totais da raiz e parte aérea das duas cultivares de milho. A cultivar Exceler em contato com Al3+ em solução apresentou menor desenvolvimento radicular quando comparada com a cultivar AG8060 mesmo sob influência do Si. A maior massa fresca e seca na raiz foi encontrada na cultivar AG8060 e a maior massa fresca e seca na parte aérea foi encontrada na cultivar Exceler, mesmo sendo sensível ao Al3+. O teor e acúmulo de Si na raiz foi maior na cultivar Exceler mostrando ser mais eficiente na absorção desse elemento. Quando as plantas ficaram maior tempo em contato com Si em solução no primeiro... / Silicon is considered as a beneficial element for plants. It has a great role in plants particularly attributed to changes in the properties of the cell wall bringing benefits against the deleterious action of aluminum. Two experiments were carried out with the aim to verify the possible effects of increasing doses of silicon against the deleterious action of Al3+ in two cultivars of corn. It was changed the root exposure time in nutritive solution containing Si. The experiments were carried out in a greenhouse of Department of Natural Resources – Soil Science, School of Agronomical Sciences – FCA/UNESP, located in Botucatu-SP. Were utilized plastic vessels with 4,5 liters of solution. The experimental design was in a randomized blocks with three replications. It was taken a 4x2 factorial, with four doses (0, 1, 2 and 4 mmol L-1 Si) and two varieties of corn - sensitive and tolerant to Al3+. After ending each period of contact with Si, it was added the Al3+ in solution, remaining for 10 days. Were evaluated the following parameters: length of plants at the initial and end periods, fresh and dry matter, content and accumulate of essential nutrients and Si and total soluble phenols in root and aerial part of both cultivars of corn. Exceler cultivar in the presence of Al3+ in solution presented less root development when compared to AG8060 cultivar even under influence of Si. The highest fresh and dry matter in roots was noted in AG8060 cultivar, and the highest fresh and dry matter in aerial part was noted in Exceler cultivar even... (Complete abstract click electronic access below)

Orientador: Leonardo Theodoro Büll / Co-orientador: João Carlos Cury Saad / Banca: Dirceu Maximino Fernandes / Banca: Takashi Muraoka / Resumo: Efeitos benéficos da adubação com silício (Si) têm sido observados em várias espécies vegetais, especialmente quando submetidas a estresse biótico ou abiótico. A utilização agronômica de resíduos provenientes do processo siderúrgico (ricos em silício) é uma alternativa hoje em dia bastante viável - são aproveitadas as características do material que podem levar à correção da acidez, incremento nos níveis de cálcio e magnésio, aumento da disponibilidade de fósforo, ferro e manganês, redução da toxicidade de alumínio, além de contribuir para a diminuição do impacto desses resíduos no meio ambiente. Este trabalho objetivou avaliar os efeitos da aplicação de Si, proveniente de resíduos de siderurgia, na nutrição, tolerância ao déficit hídrico no ajustamento osmótico, crescimento de plantas e aporte de matéria seca de seis espécies de plantas forrageiras: aveia preta (Avena strigosa Schreb), feijão-guandu (Cajanus cajan), Brachiaria decumbens, Brachiaria ruziziensis, milheto (Pennisetum americanum), crotalária (Crotalaria juncea). As plantas foram cultivadas sob três regimes de umidade no solo - plantas sem estresse hídrico, estresse moderado e estresse intenso. O ensaio foi instalado em casa de vegetação em delineamento inteiramente casualizado, em esquema fatorial duplo (5 × 3) considerando-se cinco doses de Si (0; 242; 484; 968 e 1452 kg.ha-1), três manejos hídricos correspondentes a irrigar quando a tensão de água no solo atingir -0,0232, -0,0484 e -1,5 Mpa, e seis espécies de forrageiras, acima descritas. Os parâmetros analisados foram: Análise do Resíduo Utilizado como Fonte de Si; Caracterização Química do Solo Utilizado; Massa de Matéria Seca; Teores Foliares de Macronutrientes e Silício e Teores de... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Beneficial effects of silicon fertilization (Si) have been observed in grass plants (silicon "accumulator" plants) especially under biotic or abiotic stress. The agricultural use of metallurgy slag, that presents a high level of Si, represents a viable alternative for reducing waste impacts on environment and for Soil-Plant System - are taken advantage of the material characteristics, leading to soil acidity correction, uptake in levels of calcium and magnesium, increase in availability of phosphorus, iron and manganese, reduction of aluminum toxicity. The aim of this work was to evaluate the effect of Si application, from metallurgy slag, on nourishment, drought tolerance, development of plants and dry matter uptake, of six forage plants species: black oat (Avena strigosa Schreb), pigeon pea (Cajanus cajan), Brachiaria decumbens, Brachiaria ruziziensis, pear millet (Pennisetum americanum) and sun hemp (Crotalaria juncea). Plants were cultivated under three soil moisture conditions - plants without stress, moderate stress and intensive stress. The experiment was carried out in a greenhouse, in the Soil Science Department, São Paulo State University, Botucatu, Brazil, in a completely randomized factorial design, with five doses of Si (0, 242, 484, 968 and 1452 kg ha-1), three water management systems, corresponding to irrigate when soil water tension reached -0.0232, -0.0484 and -1.5 MPa and six forage plants species. Were evaluated the following parameters: analysis of the slag used as Si source; soil chemical characterization; dry matter production; macronutrients, micronutrients and Si contents in leaves and soil, besides the biochemical parameter related to activity of Superoxide Dismutase (SOD). The use of metallurgy slag as an... (Complete abstract click electronic access below) / Mestre

Orientador: Renato de Mello Prado / Coorientador: Aguinaldo José Freitas Leal / Banca: Jairo Osvaldo Cazetta / Banca: Fábio Olivieri Nobile / Resumo: A resposta das brássicas ao nitrogênio amoniacal na solução nutritiva pode ser potencializada com adição de silício na solução, dependendo da espécie cultivada. Objetivou-se avaliar a interação do amônio com silício sobre a nutrição, fisiologia e desenvolvimento de plantas de brócolis e repolho. Utilizou-se do delineamento inteiramente casualizado, com 4 repetições, em esquema fatorial 5 x 2, correspondendo a cinco concentrações de amônio (1,3; 2,7; 5,5; 8,3 e 11,1 mmol L-1) na ausência e na presença de silício (1,0 mmol L-1). Foram realizadas as seguintes avaliações: índice de cor verde, acúmulo de nitrogênio, potássio, cálcio, magnésio e silício, na raiz e na parte aérea, fotossíntese, condutância estomática, transpiração, diâmetro de caule, área foliar, massa de matéria fresca e seca da parte aérea e seca da raiz. O fornecimento de Si na solução nutritiva potencializa a resposta em crescimento das plantas de brócolis ao amônio, não havendo efeito em repolho. Para o cultivo do brócolis e do repolho, são indicadas as concentrações de amônio de 8,6 e 7,3 mmol L-1, respectivamente, associadas ao silício apenas para o brócolis / Abstract: The response of the brassica to ammonia nitrogen in the nutrient solution can be enhanced with the addition of silicon in the solution depending on the cultivated species. It aimed to evaluate the interaction of ammonium with silicon on nutrition, physiology and development of plants in two brassicas. A completely randomized design with four repetitions was used in a factorial 5 x 2, corresponding to five ammonium concentrations (1.3, 2.7, 5.5, 8.3 and 11.1mmol L-1) in absence and presence of silicon (1.0 mmol L-1). The following evaluations were performed: green index, accumulation of nitrogen, potassium, calcium, magnesium and silicon, in the root and shoot, photosynthesis, stomatal conductance, transpiration, stem diameter, height, leaf area, fresh and dry weight of shoot and root. Nutritive solution Si supply enhances broccoli plants growth response to ammonium, with no effect on cabbage. For broccoli and cabbage cultivation, ammonium concentrations of 8.6 and 7.3 mmol L-1 are indicated, respectively, with silicon association only for broccoli / Mestre

A greenhouse study was carried out to investigate the effectiveness of soil-applied silicon (Si) with that of foliar applications for sorghum growth. Silicon sources were soil-applied as calmasil (calcium silicate) at two rates (4 and 8t/ha) and foliar applied Si including pure K-silicate, K-humate and K-fulvate (all three foliar treatments at rates of 300 and 600 ppm). Another treatment included soil applied calmasil plus low rate of foliar applied K-humate. The soils used for the greenhouse trial were Cartref, Glenrosa, Nomanci and Fernwood. Results indicated that application of calcium silicate to the soil before planting increased sorghum yield and Si uptake in three of the four soils. Silicon uptake from different experimental treatments followed the order: Calmasil 8t/ha > calmasil 4t/ha ~ calmasil + 300 ppm K-humate> K-humate = K-fulvate = pure-K silicate = control. Foliar sprays were ineffective at increasing yield, Si content of the plant tissues or Si uptake. The concentrations of exchangeable Ca, Mg as well as soil pH were significantly increased by calmasil treatments. Extractable AI concentrations were also reduced due to the Iiming effect of calcium silicate and also possibly formation of insoluble aluminosilicates. The yield response to applied calmasil seemed to be primarily related to its Iiming effect and reductions in extractable AI in the Cartref, Glenrosa and Nomanci soils. The dry matter yield was highest in Fernwood and lowest in Cartref soil. However, there was no significant yield response to calmasil in Fernwood soil which had an initial pH of 5.8 and insignificant extractable AI concentrations. Therefore application of calcium silicate had no significant effect on extractable AI concentration in this soil. Yield response to calmasil may also have been partly due to direct positive effects of applied Si on crop growth through mechanisms such as increased photosynthetic rate and reduced transpiration rate, Addition of calmasil increased the concentrations of Si in the plant tissues and reduced those of N, P and Kin Nomanci and Fernwood soils respectively. This indicates that nutrient interactions were occurring in the plant. It was concluded that foliar-application is not an effective way of applying Si to a Siresponsive crop such as sorghum when growing in soils low in extractable soil Si. This is because Si is accumulated in plant tissues in similar amounts to macronutrients. It was also concluded that in future, studies of crop response to applied Si should include the use of non-Iiming source of Si (e.g. silicic acid) so as to separate a liming effect of calcium silicate from effect of applied Si. In a laboratory study, the effects of applied silicic acid, calcium silicate and calcium hydroxide on levels of extractable P in two Si-deficient soils were investigated. Two soils (Fernwood and Nomanci soils) were treated with two rates of P and three soil amendments (calcium silicate, calcium hydroxide and silicic acid) and incubated for six weeks at room temperature. Phosphorus was extracted using Truog, AMBIC and resin methods, and levels of exchangeable and solution AI and extractable and solution Si were also measured. Application of calcium silicate and calcium hydroxide increased soil pH in both soils while silicic acid additions had no significant effect compared with the control. The pH increase was much greater in the Fernwood than Nomanci soil because of the low buffering capacity of the sandy Fernwood soil. Exchangeable AI and concentrations of monomeric and total AI in soil solution generally followed the order: control ~ silicic acid> calcium silicate> calcium hydroxide. The lowering of soluble AI concentrations in the silicic acid treatments was attributed to formation of insoluble aluminosilicate compounds while that in the calcium silicate and calcium hydroxide treatments was attributed to their Iiming effects causing a rise in pH. Concentrations of Si in soil solution were lower in the calcium hydroxide than the control treatment suggesting the solubility of Si decreased with increased pH. Additions of both Si sources increased Si concentrations in solution and the effect was more marked for the calcium silicate treatment. This was attributed to formation of insoluble aluminosilicates in the silicic acid treatment. Concentrations of H2S04extractable Si with treatment did not closely follow the same trends as those for Si concentrations in soil solution. That is, levels of extractable Si were very much higher in the calcium silicate than silicic acid treatment in both soils. In addition, concentrations of extractable Si in the calcium hydroxide treatment were similar to control in the Nomanci soil, while for the Fernwood soil, concentrations in the calcium hydroxide treatment were exceptionally high. It was suggested that liming with calcium silicate or calcium hydroxide had rendered some Si-containing compounds in the soil acid-extractable and that the nature of acid-extractable Si fraction need further study in future. The quantities of P extracted from the two soils by the various extractants followed the order: Truog> AMBle> resin. The greatest increase in extractable P induced by additions of P was recorded for Truog P and the least for resin P. The effects of Iiming (addition of calcium silicate or calcium hydroxide) on extractable P levels differed depending on the soil and extractant used with increase, decrease or no effect being recorded. Such results confirm the complexity of lime and P interactions which occur in acid soils. Additions of silicic acid had no effect on levels of extractable P, compared to control. It was suggested that the reason for this was that phosphate is adsorbed to AI and Fe oxide surfaces much more strongly than silicate. As a result, additions of Si are ineffective at increasing extractable P levels. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

The South African avocado industry is export-orientated with forty percent of total production sold overseas. The avocado fruit is a highly perishable product with a relatively high rate of respiration which results in the quick deterioration of fruit quality. Good phytosanitary procedures are a necessity in ensuring good product quality. Due to the threat of pests and diseases becoming resistant to the conventional chemicals currently used to control them, there has been a great need to diversify from their usage. Silicon (Si), being the second most abundant element (28%) in the earth’s crust after oxygen, is a major constituent of many soils and has been associated with disease resistance in plants for a long time. It has been used in a number of crop species to provide resistance against pathogenic agents. In some horticultural crops Si has been found to offer protection against fungal infections by strengthening cell walls, thus making it more difficult for the fungi to penetrate and colonize the plant. The aim of this research was to investigate the effects of postharvest silicon application on the quality of ‘Hass’ avocado fruit. The specific objectives included investigating the effect of silicon on the ripening pattern as well as the metabolic physiology of the avocado fruit. Avocado fruit were obtained from two locations in the KZN Midlands (Everdon Estate in Howick and Cooling Estate in Wartburg). Fruit were treated with different forms of Si (potassium silicate (KSil), calcium silicate (CaSil), sodium silicate (NaSil) and Nontox-silica® (NTS)) at concentrations ranging from 160 ppm to 2940 ppm. After dipping for 30 minutes in the silicon treatments, the fruit were stored at -0.5°C, 1°C, 5°C or at room temperature (25°C). Energy dispersive x-ray (EDAX) analysis was then conducted on the exocarp and mesocarp tissues to determine the extent of silicon infiltration within each treatment. Firmness measurements, ethylene evolution and CO2 production were recorded as fruit approached ripening. The CO2 production of fruit that were stored at room temperature was analysed daily until they had fully ripened, while fruit from cold storage were removed weekly to measure respiration. Mesocarp tissue from each fruit was extracted using a cork borer and subsequently freeze-dried and stored for physiological analysis. The freeze-dried mesocarp tissue was then finely ground and later analysed for sugar content, total anti-oxidant capacity (TAOC), total phenolic (TP) content and phenylalanine ammonia lyase (PAL) activity using their respective assays. Statistical analyses were carried out using GenStat® version 11 ANOVA. Treatment and storage temperature means were separated using least significant differences (LSD) at 5% (P = 0.05). The experimental design in this study was a split-plot design with the main effect being storage temperature and the sub-effect being treatments. Each replication was represented by a single fruit. EDAX analysis revealed that Si passed through the exocarp into the mesocarp tissue in fruit treated with high concentrations of silicon, i.e., KSil 2940 ppm. Significant differences (P < 0.001) were observed in temperature means with regards to firmness. Fruit treated with KSil and NTS only and stored at 5°C were firmer than fruit stored at other temperatures. Fruits treated with Si in the form of KSil 2940 produced the least amount of CO2, while non-treated fruits (Air) had the highest respiration rate. Fruit stored at room temperature (25°C) produced significantly higher amounts of CO2 and peaked much earlier than fruit stored at other temperatures. Ethylene results showed that there were differences (P < 0.05) between temperature means with the highest net ethylene being produced by fruit stored at 25°C. There were also significant differences amongst treatment means (P < 0.001), with fruits treated with KSil 2940 ppm producing the least ethylene. There were significant differences (P < 0.001) in temperature means with regards to the total phenolic concentration with fruits stored at 1°C having the highest TP concentration (26.4 mg L-1 gallic acid). Fruit treated with KSil 2940 ppm had the highest total phenolic concentration whilst the control fruit (Air and Water) had the lowest. There were also differences (P < 0.05) in storage temperature means with respect to the total antioxidant capacity. Fruit stored at -0.5°C had the highest TAOC (52.53 μmol FeSO4.7H2O g-1 DW). There were no significant differences in TAOC (P > 0.05) with regards to treatment means although fruit treated with KSil 2940 ppm and stored at -0.5°C showed the highest TAOC of 57.58 μmol FeSO4.7H2O g-1 DW. With regards to the concentration of major sugars in avocado, mannoheptulose and perseitol (mg g-1), no significant differences (P > 0.05) were observed in temperature means. However, fruit stored at -0.5°C had the highest concentration of these C7 sugars compared with fruit stored at other temperatures. There were significant differences in treatment means (P < 0.001) showing that fruit treated with KSil 2940 ppm had the highest concentration of both mannoheptulose (18.92 mg g-1) and perseitol (15.93 mg g-1) in the mesocarp tissue. Biochemical analyses showed differences (P < 0.05) in storage temperature means with respect to PAL enzymatic activity. Fruit stored at 5°C had the highest PAL activity (18.61 mmol cinnamic acid g-1 DW h-1) in the mesocarp tissue compared with fruit stored at other temperatures. There were significant differences in treatment means (P < 0.001) with regard to PAL activity. Fruit treated with KSil 2940 ppm had the highest PAL activity (23.34 mmol cinnamic acid g-1 DW h-1). This research has demonstrated the beneficial effects, particularly applications of 2940 ppm Si in the form of KSil. This treatment successfully suppressed the respiration rate of avocado fruit. Biochemical analyses of total antioxidants, total phenolics and PAL activity in the mesocarp tissue have shown the usefulness of Si in improving the fruit’s metabolic processes. The C7 sugars (D-mannoheptulose and perseitol) also seem to be more prevalent in avocado fruit treated with Si (particularly KSil 2940 ppm) than in non-treated fruit. This suggests that an application of Si to avocado fruit can aid in the retention of vital antioxidants (C7 sugars). / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2008. / Full text also available online. Scroll down for electronic link.

Although silicon (Si) has not yet been recognized as an essential nutrient element, its application to sugarcane (Saccharum officinarum L.) has proved to be beneficial. Since optimum crop production depends on the maintenance of adequate plant nutrients in the soil, there is a need in the South African sugar industry for a reliable index for assessing the requirement for supplemental silicon (Si) in soils, particularly in reducing the risk of Eldana saccharina stalk borer infestation in cane. The objective of this study was to assess Si availability in soils, to select a suitable Si extraction method and a critical value for determining when a response is likely. For this purpose, five acid soils (representing. some of the most important agricultural soil groups used for sugarcane production in the sugar belt) were used in October 2004, in the lAKE WILSON glasshouse of the South African Sugarcane Research Institute (SASRI) based at Mount Edgecombe. Except for the Arcadia form soil with an initial Si content of 1.2 mmol kg- I as estimated using the O.OlM H2S04 + (NH4)zS04) extractant, soils representing the other five soil forms namely Cartref, Glenrosa, Longlands and Nomanci; exhibited a sub-optimal Si content of not more than 4.0 mmol kg-I. Sorghum was used as a plant crop and sugarcane as a ratoon crop because of their Si accumulator status. Three different Si sources: calmasil, slagment and wollastonite; with respectively 9.85, 15.20, and 5.25% Si content were applied at increasing rates of 0, 3 and 6 tons ha- 1 as Si fertilizers. Silicon (Si) was extracted from untreated and treated soils by utilizing six different extractants, (1) O.OlM H2S04 + (NH4)2S04; (2) Distilled water; (3) 0.025M H2S04; (4) 0.5M CH3COOH; (5) 0.5M CH3COONH4pH 4.8; and (6) O.OlM CaCh.2H20. The amount of soil Si extracted followed the order: 0.025M H2S04 > 0.5M CH3COOH > O.OlM H2S04 + (NH4)2S04 > O.OlM CaCh.2H20 > 0.5M CH3COON~ pH 4.8 > distilled water. Soil Si extracted by 0.025M H2S04 was significantly correlated with soil exchangeable cations,. CEC, clay content, cane biomass yield, cane Si uptake and increasing rates of applied Si. Averaged over all soil forms investigated, the increases in dry biomass yield and Si uptake ranged. from 18% to 154% for sorghum; and from 23% to 85% for cane respectively. Even though the highest increases (%) in cane biomass yield and Si uptake were obtained on a Nomanci form soil with initial poor fertility status, the highest means were obtained on an Arcadia form soil with the highest Si initial content. There was no difference between different Si sources in their ability to influence cane biomass yield and Si uptake, and therefore the supply to the soils. Even though the lower and higher Si source rates were not different from each other, they increased cane yield and Si uptake, indicating that Si was undoubtedly beneficial for sugarcane. The Si critical levels for different soils as estimated by 0.025M H2S04 were 6.0 mmol kg-1 (168 mg kg-I) for Arcadia; 2.6 mmol kg-I (64 mg kg-I) for Cartrel; 2.5 mmol kg-I (64 mg kg-I) for Glenrosa; 1.6 mmol kg-I (45 mg kg-I) for Longlands; and 2.4 mmol kg-I (67 mg kg-i) for Nomanci form soils. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.