Ratoon stunting disease (RSD), caused by the bacterium Leifsonia xyli subsp xyli, is well established in most sugarcane growing regions of the world and is considered to cause more yield losses worldwide than any other sugarcane disease (Hughes, 1974). In South Africa, field trials have demonstrated that yield reductions under rainfed conditions can exceed 40% in highly susceptible varieties (Bailey and Bechet, 1986). When cane is grown under irrigation, yield losses are less noticeable but still significant in many varieties (Bailey and Bechet, 1995). It is estimated that RSD currently results in a one percent reduction in industrial production in South Africa and between 10 and 20% in other African countries where South African varieties are grown (Bailey and McFarlane, 1999; Rutherford et al., 2003). For many years, the reaction of different sugarcane varieties to RSD has been based on large, replicated yield loss trials grown over a number of years under rainfed and irrigated conditions. Although these trials provide valuable information, they are time-consuming and require large areas of uniform land. They are therefore not suitable for incorporation into a routine disease screening programme in which large numbers of genotypes are assessed for their reactions to the important diseases occurring in the industry. As a result, the susceptibility of new commercial varieties to RSD is only known several years after release to the growers. The main objective of this study was to establish a suitable method to reliably evaluate sugarcane genotypes for RSD resistance as part of the plant breeding and selection programme. Emphasis was placed on the use of the tissue blot immunoassay (TBlA) developed by Harrison and Davis (1988) and modified by Davis et al (1994), in relation to the more traditional methods of variety assessment, such as the rate of spread of RSD in the field at harvest and yield loss trials. Although the immunoassay protocol was not altered, slight modifications to the blotting procedure resulted in clearer blots that were easier to interpret. Internode position and the age of the cane were shown to have a marked effect on the extent of colonisation and ultimately the RSD resistance rating. A trial investigating the effect of the extent of colonisation on the rate of spread of RSD at harvest was conducted and showed that the relationship between spread and colonisation was highly significant. This indicated that RSD spread more rapidly through varieties such as N14 and N22 that supported high populations of L. xyli subsp xyli. The control plots in the same trial provided useful information on the extent of colonisation in the twelve varieties planted. In another trial, the effect of RSD on the yield components of six commercially grown varieties was investigated and TBIA was also conducted to compare the two methods of variety assessment. The relationship between yield loss and the extent of colonisation was significant in both the plant and first ratoon crops. TBIA produced consistent results and the ranking of the six varieties was virtually identical, despite the different growing conditions during the two crop cycles. In an attempt to screen large numbers of genotypes under controlled glasshouse conditions, .TBIA was also tested on RSD-infected sugarcane transplants (seedlings). The results of this trial were variable and could not be reliably used as a screening tool. Based on the findings of this study, TBIA has now been adopted as a quicker and cheaper alternative to immunofluorescence microscopy for diagnosing RSD in sugarcane transplants. More importantly, TBIA has been accepted as a method of screening genotypes routinely for resistance to RSD and the first screening trial was planted in November 2002. It will now be possible to inform sugarcane growers of the RSD status of the new varieties as they are released, enabling them to make more informed decisions on how to manage each variety. This information will also be valuable when selecting parents in the crossing programme, with a long term view of improving the general resistance of commercially grown varieties to RSD. This should ultimately result in a substantial reduction in RSD levels in the industry. / Thesis (M.Sc.)-University of Natal, Durban, 2003.

Made available in DSpace on 2014-06-11T19:28:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-02-24Bitstream added on 2014-06-13T20:18:15Z : No. of bitstreams: 1 borges_bmmn_me_jabo.pdf: 294740 bytes, checksum: aa89f904a1201e91b8e3415febff98f6 (MD5) / O sistema de colheita da cana-de-açúcar sem despalha a fogo acumula palha na superfície do solo e pode alterar o manejo do nitrogênio na cultura, especialmente com uso do silício. Objetivou-se avaliar os efeitos da aplicação de nitrogênio em cobertura associado ao silicato e calcário nas propriedades químicas do solo, no estado nutricional e na produção da soqueira de cana-de-açúcar. O experimento foi desenvolvido na segunda soqueira de cana-de-açúcar com colheita sem despalha a fogo, cultivada em Latossolo Vermelho distrófico. Os tratamentos foram constituídos de doses de nitrogênio 0; 40; 80; 120 e 160 kg ha-1 na forma de ureia, e duas fontes de materiais corretivos, silicato de cálcio e magnésio (presença de Si) e calcário (ausência de Si). Foram avaliados os efeitos dos tratamentos nos atributos químicos do solo, no desenvolvimento, produção de massa seca, nutrição, produtividade e na qualidade tecnológica da segunda soqueira. O uso do nitrogênio associado aos corretivos não afetou a fertilidade do solo, entretanto, o uso do silicato aumentou o teor de Si do solo aos 12 meses após a brotação da cana-de-açúcar. As variáveis de desenvolvimento não foram afetadas pela aplicação dos tratamentos, exceto número de colmos na época da colheita, apresentando aumento na presença do silício. As doses de N e os corretivos não afetaram o estado nutricional da cultura, porém influenciaram o acúmulo de N e Si na planta. As doses de N, independentemente do uso do silicato, aumentaram a produtividade da soqueira da cana-de-açúcar, todavia, não afetaram a qualidade tecnológica / The sugarcane harvest system without burning accumulates trash at the soil surface and can modify the culture nitrogen management especially with silicon application. The objective was to evaluate the effects of the nitrogen application associated to the silicate and to lime at the nutritional status, yield and the soil chemical properties at the second sugarcane ratoon. The experiment was carried out at the second sugarcane ratoon harvested without burning the trash, cultivated in an Oxisol. The treatments were constitute of nitrogen rates 0; 40; 80; 120 and 160 kg ha-1, urea, and two sources of corrective materials, calcium and magnesium silicate (presence of Si) and lime (absence of Si). Were evaluated the treatment effects at the soil chemistry attributes, sugarcane development, dry matter plant nutrition, productivity and yield, and the technological quality of the second sugarcane ratoon. The use of nitrogen associated to the use of silicate and lime did not affect the soil fertility, however, the use of silicate increased the soil silicon content 12 months after sugarcane sprouting. The development variables were not affect by the application of the treatments, except for number of culms at the harvesting period, showing increase at silicon presence. The N rates and the correctives did not affect the culture nutritional status, yet they affected the N and Si accumulation in the plant. The N rates independently of the use of silicate increased the sugarcane ratoon yield, though, did not affect the technological quality

Orientador: Renato de Mello Prado / Banca: João Chrisóstomo Pedroso Neto / Banca: Miguel Angelo Mutton / Resumo: O sistema de colheita da cana-de-açúcar sem despalha a fogo acumula palha na superfície do solo e pode alterar o manejo do nitrogênio na cultura, especialmente com uso do silício. Objetivou-se avaliar os efeitos da aplicação de nitrogênio em cobertura associado ao silicato e calcário nas propriedades químicas do solo, no estado nutricional e na produção da soqueira de cana-de-açúcar. O experimento foi desenvolvido na segunda soqueira de cana-de-açúcar com colheita sem despalha a fogo, cultivada em Latossolo Vermelho distrófico. Os tratamentos foram constituídos de doses de nitrogênio 0; 40; 80; 120 e 160 kg ha-1 na forma de ureia, e duas fontes de materiais corretivos, silicato de cálcio e magnésio (presença de Si) e calcário (ausência de Si). Foram avaliados os efeitos dos tratamentos nos atributos químicos do solo, no desenvolvimento, produção de massa seca, nutrição, produtividade e na qualidade tecnológica da segunda soqueira. O uso do nitrogênio associado aos corretivos não afetou a fertilidade do solo, entretanto, o uso do silicato aumentou o teor de Si do solo aos 12 meses após a brotação da cana-de-açúcar. As variáveis de desenvolvimento não foram afetadas pela aplicação dos tratamentos, exceto número de colmos na época da colheita, apresentando aumento na presença do silício. As doses de N e os corretivos não afetaram o estado nutricional da cultura, porém influenciaram o acúmulo de N e Si na planta. As doses de N, independentemente do uso do silicato, aumentaram a produtividade da soqueira da cana-de-açúcar, todavia, não afetaram a qualidade tecnológica / Abstract: The sugarcane harvest system without burning accumulates trash at the soil surface and can modify the culture nitrogen management especially with silicon application. The objective was to evaluate the effects of the nitrogen application associated to the silicate and to lime at the nutritional status, yield and the soil chemical properties at the second sugarcane ratoon. The experiment was carried out at the second sugarcane ratoon harvested without burning the trash, cultivated in an Oxisol. The treatments were constitute of nitrogen rates 0; 40; 80; 120 and 160 kg ha-1, urea, and two sources of corrective materials, calcium and magnesium silicate (presence of Si) and lime (absence of Si). Were evaluated the treatment effects at the soil chemistry attributes, sugarcane development, dry matter plant nutrition, productivity and yield, and the technological quality of the second sugarcane ratoon. The use of nitrogen associated to the use of silicate and lime did not affect the soil fertility, however, the use of silicate increased the soil silicon content 12 months after sugarcane sprouting. The development variables were not affect by the application of the treatments, except for number of culms at the harvesting period, showing increase at silicon presence. The N rates and the correctives did not affect the culture nutritional status, yet they affected the N and Si accumulation in the plant. The N rates independently of the use of silicate increased the sugarcane ratoon yield, though, did not affect the technological quality / Mestre

Sugarcane is harvested during nine months per year in Brazil with a wide range of water balance that ultimately affect response to nitrogen (N). However, a single N rate of approximately 1.1 kg N per Mg of sugarcane produced is used over the harvest season, applied as a single application few weeks after sugarcane harvest. In addition, there is a trend of growers to increase N rates in the green cane trash blanketing system (GCTB) of Brazil. This study aimed to test the hypothesis that optimal N management will be achieved by means of ascertaining N rates in each harvest season through split instead of single application. Five field trials were conducted in each harvest season (autumn: April to June; winter: July to September; and spring: October to December) across center-south region of Brazil in the 2016/2017 crop season. The experimental design was a N response curve with the N rates being defined according the yield obtained in the previous season (0.8; 1.0; 1.2 and 1.4 kg N per Mg sugarcane; plus an additional control); additional treatments with split N application were tested in autumn and winter, but not in spring. Sugarcane harvested during autumn presented higher response to N when compared to areas harvested in winter or spring. Higher responsiveness to N can be related to the lower water deficit suffered from sites harvested during autumn. Split application showed a limited but positive potential in increasing yields by 2.3 Mg ha-1 during autumn, but not in winter. Nitrogen rates of 1.0, 0.8, and 0.8 kg N Mg-1 can be recommended for sugarcane areas harvested respectively in autumn, winter and spring of center south, Brazil. The finding of this study is that optimal N management should consider the harvest time to ascertain N rates for profitable sugarcane production. / A cana-de-açúcar é colhida nove meses por ano no Brasil, com uma ampla variação no balanço hídrico, o que afeta significativamente a resposta ao nitrogênio (N). Contudo, uma única dose de aproximadamente 1,1 kg N por Mg de cana-de- açúcar produzida é usualmente utilizada durante esse período, aplicada em uma única vez algumas semanas após a colheita. Além disso, há uma tendência dos produtores em aumentar as doses de N em função do sistema brasileiro de colheita de cana crua. Este estudo objetiva testar a hipótese de que um manejo otimizado de N será alcançado por meio da averiguação de doses de N em cada época de colheita através do parcelamento ao invés de aplicação única. Cinco experimentos de campo foram conduzidos em cada época de colheita (começo de safra: abril a junho; meio de safra: julho a setembro; final de safra: outubro a dezembro) na região centro-sul do pais durante a safra 2016/2017. O delineamento experimental foi uma curva de resposta a doses de N, sendo as doses definidas de acordo com a produtividade obtida na última colheita (0,8; 1,0; 1,2 e 1,4 kg N por Mg de cana-de-açúcar; mais um controle); tratamentos adicionais com parcelamento de N foram testados no começo e meio de safra, mas não no final de safra. A cana-de-açúcar colhida no início de safra apresentou a maior resposta a N quando comparada às áreas colhidas no meio ou final de safra. Maior potencial de resposta a N pode estar relacionado ao menor déficit hídrico sofrido nos locais colhidos em início de safra. O parcelamento de N mostrou potencial positivo, mas limitado de resposta ao aumentar a produtividade de colmos em 2,3 Mg ha-1 no início de safra, mas não no meio de safra. Doses de 1,0; 0,8 e 0,8 kg N Mg-1 podem ser recomendadas para áreas colhidas no inícios, meio e final de safra, respectivamente, no centro-sul do Brasil. A descoberta desse trabalho é que o manejo otimizado do nitrogênio deve considerar a época de corte visando ajustar as doses de N para produção rentável de cana-de-açúcar.