No description available.

No description available.

No description available.

No description available.

Call number: LD2668 .T4 1959 O38

Ph.D, Faculty of Science, University of the Witwatersrand, 2011 / Abstract Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae) (water hyacinth), a neotropic noxious weed of South American origin, is counted among the “big five” aquatic weeds in South Africa. The weed causes dramatic ecological and economic losses in infested areas. Its control is facilitated by the release of biocontrol agents, mainly Neochetina eichhorniae (Warner) and Neochetina bruchi Hustache (Coleoptera: Curculionidae). Control efforts via biocontrol are hampered, mainly by the climate incompatibility of the agents, aggravated further by the indiscriminate use of lethal doses of glyphosate based herbicides. The lethal doses interfere with the successful establishment and persistence of the biocontrol agents, thus undermining their impact. Continued use of herbicide kills the water hyacinth mat and as a result, the immature stages of the agents are killed. If biocontrol is to succeed as a control strategy, then low doses of the herbicide need to be advocated. It was hypothesized that a low dose will constrain the vegetative and reproductive capacity of the weed, while maintaining the habitat for the biocontrol agents. Consequently, this study was conducted to identify a retardant dose of glyphosate herbicide and test its effect on the Neochetina weevils. A concentration of 0.8% (0.11g m-² or 2880mg a.i /L) glyphosate based herbicide, sprayed at 150 L ha-1 was proved to retard the vegetative and the reproductive growth of the weed, in terms of leaf and ramet production. Further, the retardant dose did not have any detrimental effects on the adult weevils and its larval stages. Weevil herbivory was also enhanced by the retardant dose. Furthermore, the retardant dose did not have any detrimental effects on ‘plant quality’ as evidenced by % nitrogen level in plant tissues such as crown and leaves. Contrary to expectation however, the combined effects of the retardant dose and Neochetina herbivory (0.8%+Ne) did not result in the production of lower number of ramets or leaves than water hyacinth plants dosed with 0.8% herbicide alone. Water hyacinth biocontrol agents in South Africa are subjected to frosty winters with low temperatures which cause the biocontrol agents to decline to an overwintering larval population that fails to catch up with the weed as it rebounds from the frost in spring. This hypothesis was tested in this study at 12 water hyacinth infested sites, which were grouped as temperate and sub-tropical sites. At both the temperate and subtropical sites, water hyacinth plants produced ramets (daughter plants) through autumn and increased biomass during summer. However, weevil numbers were very low at these sites, as evidenced by adult counts and feeding scars, indicating a marked seasonal asynchrony between the phenologies of the weevils and water hyacinth. Hence, intervention by seasonal applications of the herbicide is crucial to constrain weed growth. Herbicidal applications during autumn and spring inhibited the growth of the weed without adversely affecting the adult weevils or immature, immobile stages. Continued use of herbicides raises concerns of effect on non-target species, such as amphibians. Results from this study indicate that a direct application of a retardant dose of glyphosate did not kill or affect the growth of the Xenopus larvae, as determined by survival and body lengths. However, under laboratory conditions, this study has shown for the first time that an invasive aquatic weed (water hyacinth) was more lethal to an aquatic vertebrate (Xenopus larvae) than a herbicide advocated for its control. This study conclusively shows that retardant dose of glyphosate herbicide can be integrated with biocontrol to provide a sustainable and eco-friendly technique with which to combat water hyacinth infestations in South Africa.

A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science / Water hyacinth is one of the most invasive aquatic plants in the world. As such, there have been numerous attempts to model and predict its growth. Some of these models incorporate the influence of temperature or nutrients as the two most important determinants of water hyacinth growth. Other models include the effect of biological control on the growth of the plant, but only one model integrates environmental factors (temperature) with the effect of biological control. In this study, I attempt to incorporate temperature, and biological control effects on the growth of water hyacinth into a single model. Temperature-dependent water hyacinth and stage-structured Neochetina weevil population models were constructed in STELLA 9.1.4 and compared against an empirical dataset for two water hyacinth infested sites in South Africa for a two-year period (2004-2006). Although these models may not simulate field water hyacinth populations accurately, they suggest that Neochetina weevils can reduce water hyacinth populations, to below the assumed carrying capacity (70 kg/m2). It appears that the effects of Neochetina larvae are vital in reducing water hyacinth populations, and need to be further explored in order to simulate water hyacinth/weevil systems accurately.

Orientador: Edvaldo Aparecido Amaral da Silva / Banca: Juliana Pereira Bravo / Banca: Marcel de Almeida Silva / Resumo: Durante o processo de germinação da semente várias enzimas estão presentes em reações metabólicas importantes durante a respiração, como por exemplo, malato desidrogenase e álcool desidrogenase. Além disso, para que a germinação aconteça, são necessárias a expansão e a posterior divisão das células do embrião, nesses processos estão envolvidos os genes actina e ciclina, respectivamente. São importantes ainda, os mecanismos de proteção das sementes contra estresses abióticos durante a germinação, dentre eles podem ser citadas a presença de proteínas de choque térmico, relacionadas com a tolerância à dessecação e de enzimas como a glutationa-S-transferase, consideradas antioxidantes. Objetivou-se com este estudo avaliar o perfil de expressão de genes associados com a respiração, citoesqueleto, ciclo celular e estresse no embrião de sementes de Solanum lycocarpum durante a germinação. As sementes de lobeira foram avaliadas com relação a sua qualidade fisiológica, determinando-se: porcentagem de germinação, índice de velocidade de germinação, tempo médio de germinação, frequência de germinação. Além disso, determinou-se uma curva de embebição. O RNA do embrião das sementes foi extraído aos 1, 5, 10 e 15 dias de embebição em água seguido da síntese de cDNA. A expressão gênica foi realizada usando-se a técnica de PCR em tempo real. Os genes estudados no embrião foram malato desidrogenase (MDH), álcool desidrogenase (ADH2), actina (ACT7), ciclina (CDC2), proteína de choque térmico (HSPS17.6), glutationa-S-transferase (GST). A partir dos resultados obtidos conclui-se que, durante o processo de germinação de sementes de lobeira, existe variação no perfil de expressão de ... / Abstract: During the process of seed germination various enzymes are present in important metabolic reactions during respiration, such as malate dehydrogenase and alcohol dehydrogenase. In addition, for germination to take place, is necessary expansion and subsequent division of the cells of the embryo, which requires the involved of the genes cyclin and actin, respectively. Mechanisms associated with seed protection against abiotic stresses during germination, among which may be mentioned is the presence of heat shock proteins related to desiccation tolerance and enzymes such as glutathione-S-transferase, considered as antioxidant. The aim of this study was to evaluate the expression profile of genes associated with respiration, cytoskeleton, cell cycle and stress in the embryo of seeds of Solanum lycocarpum during germination. Lobeira seeds were evaluated with respect to their physiological quality, determining: germination percentage, speed of germination, means germination time, frequency of germination and was also given a curve of soaking. The RNA from the embryo of the seeds was extracted at 1, 5, 10 and 15 days of imbibitions in water, followed by cDNAS synthesis The gene expression was carried out using the technique of real time PCR. The genes studied in the embryo were malate dehydrogenase (MDH), alcohol dehydrogenase (ADH2) and actin (ACT7), cyclin (CDK2), heat shock protein (HSPS17.6), glutathione-S-transferase (GST). From the results obtained we concluded that, during the process of germination of lobeira, there is variation in the expression of genes associated with respiratory, stress protection and expansion and cell division / Mestre

A seleção de biótipos de plantas daninhas resistentes ao herbicida glyphosate no Brasil vem crescendo a cada ano em conseqüência principalmente da dependência dos principais sistemas de produção a este herbicida. Este fenômeno é evidente na citricultura brasileira, onde o glyphosate é o principal herbicida utilizado no controle de plantas daninhas há anos. As infestações da planta daninha conhecida como buva na citricultura é composta da mistura de duas espécies, Conyza canadensis e C. bonariensis, que apresentam ciclo de vida anual ou bianual, e são espécies altamente adaptadas a agroecossistemas com baixo distúrbio mecânico no solo, sendo nos sistemas de produção citrícolas altamente prolíficas. A suspeita de seleção de biótipos de buva resistente ao herbicida glyphosate motivou o desenvolvido desta pesquisa com o objetivo de comprovar a existência de biótipos resistentes, identificar suas principais características de crescimento e estudar alternativas de controle desses biótipos. A comprovação da existência dos biótipos resistentes ao glyphosate foi feita através de curvas dose-resposta, onde se verificou que o nível de resistência (GR50 do biótipo resistente (R) dividido pelo GR50 do biótipo suscetível (S)) está entre 6,15 a 10,79 para os biótipos da espécie Conyza canadensis e entre 1,52 a 14,75 para os biótipos da espécie Conyza bonariensis. Com relação ao estudo de herbicidas alternativos ao glyphosate no seu controle, comparando a aplicação dos herbicidas estudados em plantas de buva sob dois estádios fenológicos, verificou-se que os níveis de controle (%) em plantas com até 10 folhas de desenvolvimento foram de 88, 81,5 e 76,6% respectivamente para os tratamentos com glyphosate + bromacil + diuron (1.440 + 1.200 + 1.200 g ha-1), glyphosate + atrazina (1.440 + 1.500 g ha-1) e glyphosate + diuron (1.440 + 1.500 g ha-1), considerados como mais eficazes; já em plantas em estádio de desenvolvimento reprodutivo, as melhores alternativas de controle foram os tratamentos que continham o herbicida amônio glufosinato 400 g ha-1. O crescimento vegetativo, baseado na biomassa seca de raízes e parte aérea e área foliar, dos biótipos resistentes de ambas as espécies comparados com o seu respectivo biótipo suscetível foi menor que o das plantas resistentes. A umidade demonstrou-se como o principal fator de interferência da germinação de buvas na região de Matão-SP. Dessa maneira, a presente pesquisa comprovou a resistência dos biótipos estudados ao herbicida glyphosate, destacando as diferenças de crescimento entre os biótipos; a eficácia dos herbicidas alternativos de manejo dos biótipos resistentes de buva ao glyphosate é dependente do estádio fenológico de desenvolvimento da planta daninha, sendo o herbicida amônio-glufosinato excelente alternativa de controle do biótipo resistente ao glyphosate. / The selection of weed biotypes resistant to glyphosate in Brazil has been increasing each year, as a consequence of the over reliance of the main cropping systems to this herbicide. This phenomenon is observed in citrus production systems, where glyphosate is the main herbicide used for weed control for several years. The infestation of the weed known as horseweed is composed by the mixture of two species, Conyza canadensis and Conyza bonariensis, that present annual or biannual life cycle, and adaptation to agroecossystems with low mechanical disturbance in the soil, being in the citrus production systems highly prolific. The suspicion of glyphosate resistant biotypes of horseweed motivated the development of this research with the objective of detecting the existence of resistant biotypes, identifying the main characteristics of growth and development and studying alternatives of control of these resistant biotypes. By using dose-response curves it was possible to verify that the level of resistance (GR50 of the resistant biotype (R) divided by the GR50 of the susceptible biotype (S)) is between 6,15 and 10,79 for the biotypes of the species Conyza canadensis and between 1,52 and 14,75 for the biotypes of the species Conyza bonariensis. With regard to the best control herbicide alternatives of control, comparing horseweed plants at different phonological stages, it was observed that the control level (%) in plants at 10 leaves of development were of 88.0, 81.5 and 76.6% respectively for the treatments with glyphosate + bromacil + diuron (1,440 + 1,200 + 1,200 g ha-1), glyphosate + atrazina (1,440 + 1,500 g ha-1) e glyphosate + diuron (1,440 + 1,500 g ha-1), considered as the most effective treatments; for the plants at reproductive stage, the best alternatives of control were the treatments with ammonium glufosinate. The growth based on shoot and root dry biomass and leaf area of the resistant biotypes of both species compared to the susceptible biotype of the respective species were lower than of the resistant plants, but the resistant plants have higher seed production potential, The humidity was the main factor to interfere the germination on Matão-SP. Therefore, it is possible do conclude from this research that the biotypes studied are resistant to glyphosate, and they have the same competitiveness compared to the susceptible ones; the efficacy of the alternative herbicides for management of the resistant biotypes of horseweed to glyphosate depends on the development stage of the weed.

Typescript (photocopy). / Digitized by Kansas Correctional Industries