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O método sorológico \"tissue blot enzyme immunoassay\" foi utilizado para determinar a taxa de colonização dos vasos do xilema por Leifsonia xyli subsp. xyli (Lxx) em colmos de 28 variedades de cana-de-açúcar, incluindo a CB47-355, CB41-76 e CB49-260 como padrão resistente, intermediário e suscetível, respectivamente. Para cada variedade, 16 gemas foram tratadas termicamente a 50,5ºC por 2 horas e, em seguida, submetidas a banho fungicida a base de benomyl na dose de 6,5 g do princípio ativo por 10 litros de água. Oito gemas foram imersas por 10 minutos em caldo da CB49-260 sabidamente colonizada por Lxx diluído em água destilada na proporção 1:5 (\"INOCULADO\") e a outra metade em água (\"SADIO\"). Após a inoculação, foram plantados três vasos (repetições) para o tratamento, sendo as plantas mantidas em casa-de-vegetação até a colheita durante 7 meses, quando então 2 colmos de cada vaso foram amostrados para determinar a taxa de colonização dos vasos. A variedade CB47-355 não apresentou nenhum vaso colonizado, enquanto na CB41-76 e CB49-260 a taxa de colonização foi igual a 17% e 76%, sendo classificadas como resistente, intermediária e suscetível, respectivamente, concordando com literatura prévia. Das variedades em teste, 12 comportaram-se como intermediárias e 13 como suscetíveis. No primeiro caso, a %VC variou de 7 a 25 e, nas suscetíveis, de 25,7 a 76. Portanto, o aumento da taxa de colonização é praticamente linear da mais resistente para a mais suscetível, o que é característico de caráter quantitativo. Considerando que nenhuma variedade comercial mostrou-se resistente e que Lxx causa perdas significativas em todos os países produtores de cana-de-açúcar, sugere-se que os programas de melhoramento devem dirigir programas para a seleção de genitores e progênies para obter variedades resistentes. Enquanto isso não ocorre, atenção dever ser dada para o uso de mudas indexadas. / The tissue blot immunoassay (TBIA) for detecting Leifsonia xyli subsp. xyli (Lxx) colonized vascular bundles (CVB) were used in determining the reaction of 28 brazilian sugarcane cultivars to ratoon stunting disease (RSD), including CB47-355, CB41-76 e CB49-260 as resistant, intermediate and susceptible standards. For each cultivar, 16 buds were hot water treated at 50,5 oC for 2 hours and protected against root rots with benomyl. Eight buds of each cultivar were than inoculated with infected sap of the CB49-260 diluted 1:5 in water, and the remaining 8 buds were inoculated with distilled water for planting the control plots. The reps of each cultivar were planted in plastic plots at green house. At harvesting, seven months after planting, two stalks were sampled from each plot. The rate of colonization of vascular bandles by Lxx in stalks of each cultivar was determined. Statistical analysis by the univariate clustering method (Scott-Knott) was reliable for grouping genotypes according to their levels of Lxx resistance by the percentage of CVB. The cultivar CB47-355 did not present any CVB, while CB41-76 and CB49-260 presented 17% and 76%, being classified as resistant, intermediate and susceptible, in agreement with previous literature. Among the varieties in test, 12 were intermediates and 13 susceptibles. The percent of CVB among the intermediate and susceptible cultivars varied from 7% to 25% and 25,7 to 76%, respectively. The knowledge of resistance of each cultivar is essential for advising the use of complementary phytossanitary measures to control the disease. Since all cultivars are intermediate or susceptible, the sugarcane breeding programs need specific works for selection and releasing of resistant cultivars. Before this, schemes of nurseries and the use clean seed cane are recommended.

O Brasil, maior produtor mundial de cana-de-açúcar, produzirá cerca de 642 milhões de toneladas em 9 milhões de hectares plantados da cultura na safra 2014/2015. A cana-de-açúcar, assim como a maioria das culturas semi-perenes, naturalmente perde produtividade ao longo dos cortes e o setor canavieiro se preocupa com a longevidade dos canaviais, que é limitado, entre outros fatores, por doenças bióticas. O raquitismo das soqueiras (Ratoon Stunting Disease - RSD) é considerada a doença mais importante da cultura por causar significativas perdas em produtividade. O agente causal do RSD é a bactéria Leifsonia xyli subsp. xyli (Lxx); o gênero é cosmopolita e apresenta inúmeras espécies. No entanto, a subespécie Lxx tem como único hospedeiro natural conhecido a cana-de-açúcar. O estudo de hospedeiros alternativos deste patógeno reveste-se de importância pela possibilidade de outras espécies servirem como fonte de inóculo para a cana-de-açúcar e também pela possibilidade da descoberta de um hospedeiro experimental que permita o estudo do RSD em condições experimentais mais favoráveis do que a cana-de-açúcar. O presente trabalho realizou um levantamento de possíveis hospedeiros alternativos de Lxx cultivados a partir de sementes ou coletados em áreas de cultivo de cana-de-açúcar empregando pares de primers desenvolvidos especificamente para a bactéria. O trabalho também objetivou analisar o desenvolvimento de três genótipos de sorgo após inoculações artificiais com Lxx. A bactéria não foi detectada em todos os vinte e sete hospedeiros analisados, sendo vinte e duas espécies de gramíneas, confirmando que seu único hospedeiro é a cana-de-açúcar. Por outro lado, Lxx infectou as três espécies de sorgo e causou significativa redução tanto em altura como em diâmetro das plantas comparado a plantas não infectadas. Conclui-se, portanto, que Lxx não coloniza naturalmente várias gramíneas, no entanto diferentes genótipos de sorgo podem ser usados como hospedeiros experimentais para estudos de RSD. / Brazil is the main world producer of sugarcane, with a predicted production of 642 million tons in approximately 9 million hectares in the 2014/2015 harvest. As most semi-perennial crops, its productivity is reduced along successive cropping (ratoons). Thus, increasing the longevity of sugarcane crops, which is limited by biotic diseases, is an important goal for Brazil´s sugar industry. Ratoon stunting disease (RSD) is considered the most important disease of sugarcane because it causes significant losses in productivity. RSD is caused by the bacteria Leifsonia xyli subsp. xyli (Lxx), a cosmopolitan genus with numerous species. However, to date sugarcane is the only known natural host of this pathogen. Identifying alternative hosts of Lxx is important not only because they might represent an additional source of inoculum but also because some might represent a better working model to the study of RSD than sugarcane. This study carried out a PCR-based screening of potential Lxx hosts with primers developed to specifically detect Lxx, using as source seeds or plant specimens collected in sugarcane fields. The effect of artificial inoculations of Lxx on the growth of three sorghum cultivars was also analyzed. Lxx was not detected in all twenty-seven alternative hosts tested, out of which twenty represented grass species, thus confirming the specificity of the Lxx-sugarcane relationship. In addition, Lxx infected the three sorghum genotypes and significantly reduced their height and diameter when compared to non-infected plants. It is concluded that Lxx does not infect other grass species; however sorghum genotypes can be used as experimental hosts in the study of RSD.

A cana-de-açúcar é uma das principais culturas agroindustriais do Brasil. Como outras culturas de importância econômica, é também afetada por diversos patógenos como fungos, bactérias, vírus e fitoplasmas que podem limitar sua produção. A bactéria fastidiosa Leifsonia xyli subsp. xyli (Lxx) é o agente causal do raquitismo-da-soqueira da cana-de-açúcar (RSD). Esta doença não apresenta sintomas externos característicos de fácil reconhecimento. Dessa forma, a incidência do RSD pode não ser perceptível durante inspeções visuais de campo e, assim, ser facilmente disseminado de uma região para outra. A bactéria restrita ao xilema é transmitida mecanicamente de plantas infectadas para plantas saudáveis por meio da seiva presente em ferramentas de corte e em outros equipamentos durante o plantio, o cultivo e a colheita da cultura. Em razão da importância da cana-de-açúcar e do dano causado por Lxx, este trabalho visou avaliar a termoterapia e o cultivo in vitro em dois experimentos direcionados à obtenção de plantas de cana-de-açúcar da variedade SP80-3280 livres de Leifsonia xyli subsp. xyli e, assim, fornecer subsídio para o aprimoramento das medidas atuais de controle. O primeiro experimento combinou a termoterapia de toletes de uma gema (52 °C por 30 minutos) com o cultivo de meristemas apicais de três tamanhos (0,5 mm, 1,0 mm e 1,5 mm); o segundo combinou três tempos de termoterapia (1 hora, 2 horas e 3 horas) a 50 °C em gemas laterais imaturas isoladas do tolete com o cultivo in vitro. No primeiro experimento, os resultados de RT-PCR das amostras coletadas aos 15 dias na casa de vegetação mostraram que os três tamanhos de meristemas produziram plantas com títulos bacterianos em média 25 vezes mais baixos que suas genitoras, mas não as isentaram completamente de Lxx, com exceção de 8 plantas que não apresentaram Lxx com 90 dias de cultivo (4 plantas provenientes do cultivo de meristemas de 0,5 mm, 1 planta de meristema de 1,0 mm e 3 plantas de meristemas de 1,5 mm). Além disso, os meristemas de 0,5 mm não necessariamente regeneraram plantas com títulos mais baixos da bactéria quando comparados com os meristemas de 1,0 mm e 1,5 mm, mostrando que estes tamanhos testados não apresentaram correlação direta com o nível de infecção da planta regenerada por eles. Em relação ao segundo experimento, os resultados de RT-PCR mostraram que o incremento no tempo de termoterapia proporcionou maior redução nos títulos bacterianos, sendo os tratamentos de 2 horas e 3 horas os mais bem sucedidos com média de redução de 80,08% e 81,73%, respectivamente, mas não foi capaz de eliminar a bactéria. Portanto, estes experimentos demonstram que a termoterapia associada ao cultivo de tecidos é uma metodologia promissora, pois apresentaram redução da presença da bactéria Lxx em plantas de cana-de-açúcar, mas por não terem sido totalmente efetivos na eliminação da mesma, reforça a necessidade de estudos complementares. / Sugarcane is one of the major agro-industrial crops of Brazil. Like other crops of economic importance, it\'s also affected by several pathogens such as fungus, bacteria, viruses and phytoplasmas that may limit its production. The fastidious bacterium Leifsonia xyli subsp. xyli (Lxx) is the causal agent of ratoon stunting disease in sugarcane (RSD). This disease shows no external symptoms characteristic of easy recognition. Thus, the incidence of RSD may not be noticeable during visual inspection in the field and be easily spread from one region to another. The xylem-limited bacterium is transmitted mechanically from infected plants to healthy plants by the sap present in cutting tools and others equipments for planting, growing and harvesting the crop. Due to the importance of sugarcane and the damage caused by Lxx, this work aimed to evaluate thermotherapy and in vitro culture in two experiments in order to obtain sugarcane plants of variety SP80-3280 free from Leifsonia xyli subsp. xyli and thus provide subsidy for the improvement of current control methods. The first experiment combined thermotherapy on the individual bud (52 °C for 30 minutes) and the cultivation of apical meristems of three sizes (0,5 mm, 1,0 mm and 1,5 mm); the second combined three period of thermotherapy (1 hour, 2 hours and 3 hours) at 50 °C in immature lateral buds totally isolated from the tissue source followed by in vitro culture. In the first experiment, the results of RT-PCR samples collected at 15 days in the greenhouse showed that the three sizes of meristems produced plants with bacterial titers on average 25 times lower than their mother plants, but not completely exempted them from Lxx, except 8 plants that showed no Lxx after 90 days of cultivation (4 plants were from cultivation of meristems with 0,5 mm, 1 plant from 1,0 mm meristem and 3 plants from 1,5 mm meristems size). Furthermore, the meristems of 0,5 mm does not necessarily regenerate plants with lower title of the bacteria compared with the meristems of 1.0 mm and 1.5 mm, showing that these sizes tested did not present direct correlation with the level of infection on the plants regenerated from them. Regarding the second experiment, RT-PCR results showed that the increase in time of thermotherapy provided greater reduction in bacterial titers, and the treatments of 2 and 3 hours were the most successful with average reduction of 80,08 % and 81,73%, respectively, but was not able to eliminate the bacteria. Therefore, these experiments showed that thermotherapy associated with tissue culture is a promising methodology because it reduced titer of Lxx in sugarcane, but were not fully effective in eliminating the same, reinforcing the need for complementary studies.

Studies in both children and adults indicate that waist circumference (WC), a measure of abdominal obesity is closely related to cardiovascular risk factors. The accurate identification of abdominally obese children in health screening programmes for early intervention is of importance. There are, however, concerns about using international definitions for screening purposes because in most instances these have been derived from Western populations and, therefore, may have limited usefulness to children in other parts of the world. When these cut–off points are used in developing countries, they ignore the fact that the growth patterns of children and burdens of disease vary between countries. Due to lack of population specific cut–off points for children in the developing world it may be tempting and convenient to use the same cut–off points as for children in developed countries, but such a practice runs the risk of exporting failure. Ideally, a screening tool should have both high sensitivity and specificity, and these are important considerations in choosing the definition for the detection of childhood abdominal obesity. High sensitivity is necessary to avoid failure of identifying obese children and high specificity of the screening tool ensures that non–obese children are not misclassified as obese, which may otherwise lead to unnecessary treatment and psychosocial implications of stigmatisation. Failure to identify the abdominally obese child may have more serious consequences than misclassification, since it results in an increase in adult morbidity and mortality. Therefore, the main aim of this thesis was to examine fat distribution patterns of black South African (SA) children in relation to health risk. The specific objectives were to: compare the body composition of black stunted and non–stunted children from two rural communities in South Africa; to describe and compare the age and sex specific WC percentile distribution for black SA children from different study populations and compare the WC percentile distribution with those for African–American (A–A) children and to assess the diagnostic accuracy of waist–to–height ratio (WHtR) as a marker for high blood pressure, a cardiovascular risk factor in SA children. Findings of this study demonstrated increased total adiposity in non–stunted children, but trends of increased central adiposity, measured as WHtR in stunted children. This warrants further investigation on this relationship among children older than 13 years in the African context where many children are stunted. The differences observed between the different data sets and between SA and A–A children suggest that nationally representative data should be used to develop age, sex and ethnic specific WC percentiles for this population. The results indicate clearly that the median WC of children from SA studies is smaller than those of A–A children, with a medium to large effect size for the difference. Results also suggest concern with respect to high WC values (> 80 cm) among some children. The recommended universal WHtR cut–off value of 0.5 for assessment of cardiovascular risk is not suitable for black SA children because it had low sensitivity in predicting high blood pressure. The absence of locally developed cut–off values for WC and WHtR for children warrants research due to the associations between being overweight and obese and disease outcomes. It is fundamental to detect risk at an early stage so that appropriate intervention can be initiated timeously. / Thesis (Ph.D. (Nutrition))--North-West University, Potchefstroom Campus, 2011.

Studies in both children and adults indicate that waist circumference (WC), a measure of abdominal obesity is closely related to cardiovascular risk factors. The accurate identification of abdominally obese children in health screening programmes for early intervention is of importance. There are, however, concerns about using international definitions for screening purposes because in most instances these have been derived from Western populations and, therefore, may have limited usefulness to children in other parts of the world. When these cut–off points are used in developing countries, they ignore the fact that the growth patterns of children and burdens of disease vary between countries. Due to lack of population specific cut–off points for children in the developing world it may be tempting and convenient to use the same cut–off points as for children in developed countries, but such a practice runs the risk of exporting failure. Ideally, a screening tool should have both high sensitivity and specificity, and these are important considerations in choosing the definition for the detection of childhood abdominal obesity. High sensitivity is necessary to avoid failure of identifying obese children and high specificity of the screening tool ensures that non–obese children are not misclassified as obese, which may otherwise lead to unnecessary treatment and psychosocial implications of stigmatisation. Failure to identify the abdominally obese child may have more serious consequences than misclassification, since it results in an increase in adult morbidity and mortality. Therefore, the main aim of this thesis was to examine fat distribution patterns of black South African (SA) children in relation to health risk. The specific objectives were to: compare the body composition of black stunted and non–stunted children from two rural communities in South Africa; to describe and compare the age and sex specific WC percentile distribution for black SA children from different study populations and compare the WC percentile distribution with those for African–American (A–A) children and to assess the diagnostic accuracy of waist–to–height ratio (WHtR) as a marker for high blood pressure, a cardiovascular risk factor in SA children. Findings of this study demonstrated increased total adiposity in non–stunted children, but trends of increased central adiposity, measured as WHtR in stunted children. This warrants further investigation on this relationship among children older than 13 years in the African context where many children are stunted. The differences observed between the different data sets and between SA and A–A children suggest that nationally representative data should be used to develop age, sex and ethnic specific WC percentiles for this population. The results indicate clearly that the median WC of children from SA studies is smaller than those of A–A children, with a medium to large effect size for the difference. Results also suggest concern with respect to high WC values (> 80 cm) among some children. The recommended universal WHtR cut–off value of 0.5 for assessment of cardiovascular risk is not suitable for black SA children because it had low sensitivity in predicting high blood pressure. The absence of locally developed cut–off values for WC and WHtR for children warrants research due to the associations between being overweight and obese and disease outcomes. It is fundamental to detect risk at an early stage so that appropriate intervention can be initiated timeously. / Thesis (Ph.D. (Nutrition))--North-West University, Potchefstroom Campus, 2011.

O método sorológico \"tissue blot enzyme immunoassay\" foi utilizado para determinar a taxa de colonização dos vasos do xilema por Leifsonia xyli subsp. xyli (Lxx) em colmos de 28 variedades de cana-de-açúcar, incluindo a CB47-355, CB41-76 e CB49-260 como padrão resistente, intermediário e suscetível, respectivamente. Para cada variedade, 16 gemas foram tratadas termicamente a 50,5ºC por 2 horas e, em seguida, submetidas a banho fungicida a base de benomyl na dose de 6,5 g do princípio ativo por 10 litros de água. Oito gemas foram imersas por 10 minutos em caldo da CB49-260 sabidamente colonizada por Lxx diluído em água destilada na proporção 1:5 (\"INOCULADO\") e a outra metade em água (\"SADIO\"). Após a inoculação, foram plantados três vasos (repetições) para o tratamento, sendo as plantas mantidas em casa-de-vegetação até a colheita durante 7 meses, quando então 2 colmos de cada vaso foram amostrados para determinar a taxa de colonização dos vasos. A variedade CB47-355 não apresentou nenhum vaso colonizado, enquanto na CB41-76 e CB49-260 a taxa de colonização foi igual a 17% e 76%, sendo classificadas como resistente, intermediária e suscetível, respectivamente, concordando com literatura prévia. Das variedades em teste, 12 comportaram-se como intermediárias e 13 como suscetíveis. No primeiro caso, a %VC variou de 7 a 25 e, nas suscetíveis, de 25,7 a 76. Portanto, o aumento da taxa de colonização é praticamente linear da mais resistente para a mais suscetível, o que é característico de caráter quantitativo. Considerando que nenhuma variedade comercial mostrou-se resistente e que Lxx causa perdas significativas em todos os países produtores de cana-de-açúcar, sugere-se que os programas de melhoramento devem dirigir programas para a seleção de genitores e progênies para obter variedades resistentes. Enquanto isso não ocorre, atenção dever ser dada para o uso de mudas indexadas. / The tissue blot immunoassay (TBIA) for detecting Leifsonia xyli subsp. xyli (Lxx) colonized vascular bundles (CVB) were used in determining the reaction of 28 brazilian sugarcane cultivars to ratoon stunting disease (RSD), including CB47-355, CB41-76 e CB49-260 as resistant, intermediate and susceptible standards. For each cultivar, 16 buds were hot water treated at 50,5 oC for 2 hours and protected against root rots with benomyl. Eight buds of each cultivar were than inoculated with infected sap of the CB49-260 diluted 1:5 in water, and the remaining 8 buds were inoculated with distilled water for planting the control plots. The reps of each cultivar were planted in plastic plots at green house. At harvesting, seven months after planting, two stalks were sampled from each plot. The rate of colonization of vascular bandles by Lxx in stalks of each cultivar was determined. Statistical analysis by the univariate clustering method (Scott-Knott) was reliable for grouping genotypes according to their levels of Lxx resistance by the percentage of CVB. The cultivar CB47-355 did not present any CVB, while CB41-76 and CB49-260 presented 17% and 76%, being classified as resistant, intermediate and susceptible, in agreement with previous literature. Among the varieties in test, 12 were intermediates and 13 susceptibles. The percent of CVB among the intermediate and susceptible cultivars varied from 7% to 25% and 25,7 to 76%, respectively. The knowledge of resistance of each cultivar is essential for advising the use of complementary phytossanitary measures to control the disease. Since all cultivars are intermediate or susceptible, the sugarcane breeding programs need specific works for selection and releasing of resistant cultivars. Before this, schemes of nurseries and the use clean seed cane are recommended.

A cana-de-açúcar é uma das principais culturas agroindustriais do Brasil. Como outras culturas de importância econômica, é também afetada por diversos patógenos como fungos, bactérias, vírus e fitoplasmas que podem limitar sua produção. A bactéria fastidiosa Leifsonia xyli subsp. xyli (Lxx) é o agente causal do raquitismo-da-soqueira da cana-de-açúcar (RSD). Esta doença não apresenta sintomas externos característicos de fácil reconhecimento. Dessa forma, a incidência do RSD pode não ser perceptível durante inspeções visuais de campo e, assim, ser facilmente disseminado de uma região para outra. A bactéria restrita ao xilema é transmitida mecanicamente de plantas infectadas para plantas saudáveis por meio da seiva presente em ferramentas de corte e em outros equipamentos durante o plantio, o cultivo e a colheita da cultura. Em razão da importância da cana-de-açúcar e do dano causado por Lxx, este trabalho visou avaliar a termoterapia e o cultivo in vitro em dois experimentos direcionados à obtenção de plantas de cana-de-açúcar da variedade SP80-3280 livres de Leifsonia xyli subsp. xyli e, assim, fornecer subsídio para o aprimoramento das medidas atuais de controle. O primeiro experimento combinou a termoterapia de toletes de uma gema (52 °C por 30 minutos) com o cultivo de meristemas apicais de três tamanhos (0,5 mm, 1,0 mm e 1,5 mm); o segundo combinou três tempos de termoterapia (1 hora, 2 horas e 3 horas) a 50 °C em gemas laterais imaturas isoladas do tolete com o cultivo in vitro. No primeiro experimento, os resultados de RT-PCR das amostras coletadas aos 15 dias na casa de vegetação mostraram que os três tamanhos de meristemas produziram plantas com títulos bacterianos em média 25 vezes mais baixos que suas genitoras, mas não as isentaram completamente de Lxx, com exceção de 8 plantas que não apresentaram Lxx com 90 dias de cultivo (4 plantas provenientes do cultivo de meristemas de 0,5 mm, 1 planta de meristema de 1,0 mm e 3 plantas de meristemas de 1,5 mm). Além disso, os meristemas de 0,5 mm não necessariamente regeneraram plantas com títulos mais baixos da bactéria quando comparados com os meristemas de 1,0 mm e 1,5 mm, mostrando que estes tamanhos testados não apresentaram correlação direta com o nível de infecção da planta regenerada por eles. Em relação ao segundo experimento, os resultados de RT-PCR mostraram que o incremento no tempo de termoterapia proporcionou maior redução nos títulos bacterianos, sendo os tratamentos de 2 horas e 3 horas os mais bem sucedidos com média de redução de 80,08% e 81,73%, respectivamente, mas não foi capaz de eliminar a bactéria. Portanto, estes experimentos demonstram que a termoterapia associada ao cultivo de tecidos é uma metodologia promissora, pois apresentaram redução da presença da bactéria Lxx em plantas de cana-de-açúcar, mas por não terem sido totalmente efetivos na eliminação da mesma, reforça a necessidade de estudos complementares. / Sugarcane is one of the major agro-industrial crops of Brazil. Like other crops of economic importance, it\'s also affected by several pathogens such as fungus, bacteria, viruses and phytoplasmas that may limit its production. The fastidious bacterium Leifsonia xyli subsp. xyli (Lxx) is the causal agent of ratoon stunting disease in sugarcane (RSD). This disease shows no external symptoms characteristic of easy recognition. Thus, the incidence of RSD may not be noticeable during visual inspection in the field and be easily spread from one region to another. The xylem-limited bacterium is transmitted mechanically from infected plants to healthy plants by the sap present in cutting tools and others equipments for planting, growing and harvesting the crop. Due to the importance of sugarcane and the damage caused by Lxx, this work aimed to evaluate thermotherapy and in vitro culture in two experiments in order to obtain sugarcane plants of variety SP80-3280 free from Leifsonia xyli subsp. xyli and thus provide subsidy for the improvement of current control methods. The first experiment combined thermotherapy on the individual bud (52 °C for 30 minutes) and the cultivation of apical meristems of three sizes (0,5 mm, 1,0 mm and 1,5 mm); the second combined three period of thermotherapy (1 hour, 2 hours and 3 hours) at 50 °C in immature lateral buds totally isolated from the tissue source followed by in vitro culture. In the first experiment, the results of RT-PCR samples collected at 15 days in the greenhouse showed that the three sizes of meristems produced plants with bacterial titers on average 25 times lower than their mother plants, but not completely exempted them from Lxx, except 8 plants that showed no Lxx after 90 days of cultivation (4 plants were from cultivation of meristems with 0,5 mm, 1 plant from 1,0 mm meristem and 3 plants from 1,5 mm meristems size). Furthermore, the meristems of 0,5 mm does not necessarily regenerate plants with lower title of the bacteria compared with the meristems of 1.0 mm and 1.5 mm, showing that these sizes tested did not present direct correlation with the level of infection on the plants regenerated from them. Regarding the second experiment, RT-PCR results showed that the increase in time of thermotherapy provided greater reduction in bacterial titers, and the treatments of 2 and 3 hours were the most successful with average reduction of 80,08 % and 81,73%, respectively, but was not able to eliminate the bacteria. Therefore, these experiments showed that thermotherapy associated with tissue culture is a promising methodology because it reduced titer of Lxx in sugarcane, but were not fully effective in eliminating the same, reinforcing the need for complementary studies.

O Brasil, maior produtor mundial de cana-de-açúcar, produzirá cerca de 642 milhões de toneladas em 9 milhões de hectares plantados da cultura na safra 2014/2015. A cana-de-açúcar, assim como a maioria das culturas semi-perenes, naturalmente perde produtividade ao longo dos cortes e o setor canavieiro se preocupa com a longevidade dos canaviais, que é limitado, entre outros fatores, por doenças bióticas. O raquitismo das soqueiras (Ratoon Stunting Disease - RSD) é considerada a doença mais importante da cultura por causar significativas perdas em produtividade. O agente causal do RSD é a bactéria Leifsonia xyli subsp. xyli (Lxx); o gênero é cosmopolita e apresenta inúmeras espécies. No entanto, a subespécie Lxx tem como único hospedeiro natural conhecido a cana-de-açúcar. O estudo de hospedeiros alternativos deste patógeno reveste-se de importância pela possibilidade de outras espécies servirem como fonte de inóculo para a cana-de-açúcar e também pela possibilidade da descoberta de um hospedeiro experimental que permita o estudo do RSD em condições experimentais mais favoráveis do que a cana-de-açúcar. O presente trabalho realizou um levantamento de possíveis hospedeiros alternativos de Lxx cultivados a partir de sementes ou coletados em áreas de cultivo de cana-de-açúcar empregando pares de primers desenvolvidos especificamente para a bactéria. O trabalho também objetivou analisar o desenvolvimento de três genótipos de sorgo após inoculações artificiais com Lxx. A bactéria não foi detectada em todos os vinte e sete hospedeiros analisados, sendo vinte e duas espécies de gramíneas, confirmando que seu único hospedeiro é a cana-de-açúcar. Por outro lado, Lxx infectou as três espécies de sorgo e causou significativa redução tanto em altura como em diâmetro das plantas comparado a plantas não infectadas. Conclui-se, portanto, que Lxx não coloniza naturalmente várias gramíneas, no entanto diferentes genótipos de sorgo podem ser usados como hospedeiros experimentais para estudos de RSD. / Brazil is the main world producer of sugarcane, with a predicted production of 642 million tons in approximately 9 million hectares in the 2014/2015 harvest. As most semi-perennial crops, its productivity is reduced along successive cropping (ratoons). Thus, increasing the longevity of sugarcane crops, which is limited by biotic diseases, is an important goal for Brazil´s sugar industry. Ratoon stunting disease (RSD) is considered the most important disease of sugarcane because it causes significant losses in productivity. RSD is caused by the bacteria Leifsonia xyli subsp. xyli (Lxx), a cosmopolitan genus with numerous species. However, to date sugarcane is the only known natural host of this pathogen. Identifying alternative hosts of Lxx is important not only because they might represent an additional source of inoculum but also because some might represent a better working model to the study of RSD than sugarcane. This study carried out a PCR-based screening of potential Lxx hosts with primers developed to specifically detect Lxx, using as source seeds or plant specimens collected in sugarcane fields. The effect of artificial inoculations of Lxx on the growth of three sorghum cultivars was also analyzed. Lxx was not detected in all twenty-seven alternative hosts tested, out of which twenty represented grass species, thus confirming the specificity of the Lxx-sugarcane relationship. In addition, Lxx infected the three sorghum genotypes and significantly reduced their height and diameter when compared to non-infected plants. It is concluded that Lxx does not infect other grass species; however sorghum genotypes can be used as experimental hosts in the study of RSD.

Cardiovascular disease (CVD) is a major cause of adult morbidity and mortality in developed as well as in developing countries. In black population groups, stroke is more prominent than ischaemic heart disease. This may be attributed to a combination of risk factors seen in this population group inter alia raised haemostatic markers, which favour the development of stroke since it is well known that a disturbance in the haemostatic balance (a hypercoagulable and a hypofibrinolytic state) predisposes to CVD. It is generally accepted that childhood genetic, environmental and behavioural factors lay the groundwork for the manifestation of adult CVD. Therefore, one of the studies that form part of this dissertation was a cross-sectional study to determine whether haemostatic abnormalities are already present in black African adolescents and to determine whether high risk groups exist [in relation to the following haemostatic markers: fibrinogen, factor VIII (FVIII), plasminogen activator inhibitor type 1 activity (PAI-Iact), and thrombin anti-thrombin complex (TAT)] for the development of CVD later in life. The population subdivisions were made according to gender, body fat %, maturity status, height for age Z-score, and habitual PA levels. Since behavioural factors [diet, physical activity (PA), smoking and drinking habits] are controllable determinants, it could be possible to improve CVD risk to a certain degree. Therefore, the second study that forms part of this dissertation attempted to establish whether a PA programme will successfully reduce haemostatic variables in a subset of the study population used in the first study. The reader is referred to the abstracts at the beginning of each separate study manuscript (Chapters 3 and 4), for a description of the subjects, study design and methods used in each study. The results of the cross-sectional study showed that in African adolescents (a) gender independently contributed to the variability in PAI-Iact, but that the gender difference in fibrinogen and TAT could be explained by the significant differences in fat mass and PA levels observed between the genders; (b) fibrinogen was significantly higher in the stunted compared to the non-stunted children indicating that childhood chronic malnutrition may possibly predispose independently to CVD; (c) fitness influences TAT concentrations positively and that (d) no significant differences in FVIII could be found between any of the subdivisions. As these determinants seem to be modifiable through behavioural changes and optimal nutrition status through early life, it raises a sense of urgency to develop strategies for the prevention and treatment of these risk factors. The results of the intervention study showed that an 11-week outdoor PA intervention programme had no significant effect on the haemostatic markers of African adolescents, but the results of this study should be interpreted with caution since (a) seasonal variations could have clouded the effect of the PA intervention as baseline measurements were taken in the summer and end measurements in the winter; (b) attendance of the PA sessions does not necessarily implicate compliance to the exercises given; (c) baseline values seem to play a prominent role in the changes that could be expected during an intervention and, therefore, improvements in the haemostatic profile would most likely be more significant in individuals with raised baseline levels. Similar research on African children is warranted since studies investigating PA's effect on haemostatic variables remain a topic of debate and speculation and data on African population groups are scanty. / Thesis (M.Sc. (Nutrition))--North-West University, Potchefstroom Campus, 2007