Please read the abstract in the section 00front of this document / Dissertation (MSc (Botany))--University of Pretoria, 2005. / Plant Science / unrestricted

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.

Abstract available in PDF file. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1982.

Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 152-163).

The water hyacinth (Eichhornia crassipes (Mart.) Solms-Laub (Pontederiaceae)) biological control programme makes use of tight plant-insect interactions to control the weed, by reestablishing the interactions between the plant and its natural enemies. Since the beginning of the water hyacinth biological control initiative, the impact of biological control agent herbivory on water hyacinth’s population growth and fitness have been well documented; however, very few investigations have been conducted to determine whether herbivory elicits insect-induced responses by water hyacinth. Studies were conducted to determine the presence and function of water hyacinth insectinduced responses, using the plant activator, BION®, in attempt to determine the plant hormone-mediated pathways regulating the final expressions of insect-induced defences in response to herbivory by the phloem-feeder, Eccritotarsus catarinensis (Carvalho) (Hemiptera: Miridae) and the leaf chewer, Neochetina bruchi Hustache (Coleoptera: Curculionidae). BION® (Syngenta, acibensolar-S-methyl (benzothiadiazole)) is a dissolvable, granular formulation that contains a chemical analogue of the plant hormone, salicylic acid (SA), which typically regulates defences against pathogens. The application of BION® results in the induction of the SA-mediated defence pathways in plants (activation of defences against pathogens), and consequently the inhibition of the jasmonic acid (JA)- mediated defence pathways (de-activation of defences against insect herbivores). To test for induced defence responses in water hyacinth, plants treated with BION® and then subjected to herbivory, were compared to un-treated plants that were also subjected to herbivory, BION®-only treated plants and control plants. The application of BION® did not confer resistance against the two insect herbivores, as herbivory, reductions in chlorophyll content and plant growth (leaf production and second petiole lengths) significantly increased in comparison to non-BION® treated plants. Furthermore, palatability indices significantly increased (>1.00) in BION® treated plants, reflecting increased weevil preferences for SAinduced water hyacinth plants. This concluded that SA-mediated defences are not effective against insect herbivory in water hyacinth plants, but are in fact palatable to insect herbivores, which reflects ecological and physiological costs of SA-mediated defences (pathogen defences) in water hyacinth. Biochemical analyses of leaves exhibited increases in nitrogen content in BION® treated plants. These elevated levels of nitrogenous compounds account for the increases in mirid and weevil preferences for BION® treated plants. The increases in nitrogenous compounds are probably structural proteins (e.g. peroxidises), because leaves treated with BION® increased in toughness, but only when exposed to herbivory. Regardless, insect herbivory was elevated on these leaves, probably because the nitrogenous compounds were nutritionally viable for the insects.

published_or_final_version / Botany / Master / Master of Philosophy

Thesis (Ph.D.)--Mississippi State University. Department of Plant and Soil Sciences. / Title from title screen. Includes bibliographical references.

The suitability of water hyacinth (Eichornia crassipes) as a viable feedstock for renewable energy production was investigated in this project. Water hyacinth used in this study was harvested from the Vaal River near Parys in the northwest region of the Free State province, South Africa (26°54′S 27°27′E). The wet plants were processed in the laboratory at the North-West University by separating the roots from the leaves and the stems, thus obtaining two separate water hyacinth feedstock. Characterisation of the feedstock showed that the stems and leaves are more suitable for bio-energy production than roots, due to the higher cellulose and hemicellulose content and very low lignin content of the stems and leaves. Water hyacinth was evaluated as feedstock for the production of bio-ethanol gel, bio-ethanol, bio-oil and bio-char. The recovery of water from the wet plants for use in bio-refining or for use as drip-irrigation in agriculture was also investigated. Cellulose was extracted from water hyacinth feedstock to be used as a gelling agent for the production of ethanol-gel fuel. A yield of 200 g cellulose/kg dry feedstock was obtained. The extracted cellulose was used to produce ethanol-gel with varying water content. The gel with properties closest to the SANS 448 standard contained 90 vol% ethanol and 10 vol% water, with 38 wt% cellulose. This gel was found to ignite readily and burn steadily, without flaring, sudden deflagrations, sparking, splitting, popping, dripping or exploding from ignition until it had burned to extinction, as required by SANS 448. The only specifications that could not be met were the viscosity (23,548 cP) and the high waste residue (32 wt%) left after burning. The other major concern is the extremely high costs involved with the manufacturing of ethanol-gel from water hyacinth cellulose. It can be concluded that ethanol-gel cannot be economically produced using water hyacinth as feedstock. Chemical and enzymatic extraction of water from the feedstock, which is stems and leaves or roots, showed that the highest yield of water was obtained using a combination of Celluclast 1.5 L, Pectinex Ultra SP-L and additional de-ionised water. A yield of 0.89 ± 0.01 gwater/gwater in biomass was realised. This is, however, only 0.86 wt% higher than the highest yield obtained (0.87 ± 0.01 gwater/gwater in biomass) using only Pectinex Ultra SP-L and de-ionised water. It is recommended to use only Pectinex Ultra SP-L and de-ionised water at a pH of 3.5 and a temperature of 40°C. Using one enzyme instead of two reduces operating costs and simplifies the chemical extraction process. The extracted water, both filtered and unfiltered, was not found to be suitable for domestic use without further purification to reduce the total dissolved solids (TDS), potassium and manganese levels. Both the unfiltered and filtered water were, however, found to be suitable for industrial and agricultural purposes, except for the high TDS levels. If the TDS and suspended particle level can be reduced, the extracted water would be suitable for domestic, industrial and agricultural use. The potential fermentation of the sugars derived from the water hyacinth, using ultrasonic pretreatment, was investigated. Indirect ultrasonic treatment (ultrasonic bath) proved to be a better pretreatment method than direct sonication (ultrasonic probe). The optimum sugar yield for the ultrasonic bath pretreatment with 5% NaOH was found to be 0.15 g sugar/g biomass (0.47 g sugar/g available sugar) using an indirect sonication energy input of 27 kJ/g biomass. The optimum sugar yield is lower than those reported in other studies using different pretreatment methods. Theoretically a maximum of 0.24 g ethanol can be obtained per g available sugar. This relates to an ethanol yield of 0.08 g ethanol/kg wet biomass. The low yield implies that ethanol production from water hyacinth is not economically feasible. The production of bio-oil and bio-char from water hyacinth through thermochemical liquefaction of wet hyacinth feedstock was investigated. An optimum bio-char yield of 0.55 g bio-char/g biomass was achieved using an inert atmosphere (nitrogen) at 260°C and the stems and leaves as feedstock. With the roots as feedstock a slightly lower optimum yield of 0.45 g bio-char/g biomass was found using a non-reducing atmosphere (carbon monoxide) at 280°C. The bio-oil yield was too low to accurately quantify. As water is required during thermochemical liquefaction, it was found unnecessary to dry the biomass to the same extent as was the case with the pretreatment and fermentation of the water hyacinth, making this a more feasible route for biofuel production. Bio-char produced through liquefaction of roots as the feedstock and leaves and stems as the other feedstock had a higher heating value (HHV) of 10.89 ± 0.45 MJ/kg and 23.31 ± 0.45 MJ/kg respectively. Liquefaction of water hyacinth biomass increased the HHV of the feedstock to a value comparable to that of low grade coal. This implies a possible use of water hyacinth for co-gasification. The most effective route for bio-energy production in the case of water hyacinth was found to be thermochemical liquefaction (12.8 MJ/kg wet biomass). Due to the high production costs involved, it is recommended to only use water hyacinth as a feedstock for biofuel production if no alternative feedstock are available. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2014

The suitability of water hyacinth (Eichornia crassipes) as a viable feedstock for renewable energy production was investigated in this project. Water hyacinth used in this study was harvested from the Vaal River near Parys in the northwest region of the Free State province, South Africa (26°54′S 27°27′E). The wet plants were processed in the laboratory at the North-West University by separating the roots from the leaves and the stems, thus obtaining two separate water hyacinth feedstock. Characterisation of the feedstock showed that the stems and leaves are more suitable for bio-energy production than roots, due to the higher cellulose and hemicellulose content and very low lignin content of the stems and leaves. Water hyacinth was evaluated as feedstock for the production of bio-ethanol gel, bio-ethanol, bio-oil and bio-char. The recovery of water from the wet plants for use in bio-refining or for use as drip-irrigation in agriculture was also investigated. Cellulose was extracted from water hyacinth feedstock to be used as a gelling agent for the production of ethanol-gel fuel. A yield of 200 g cellulose/kg dry feedstock was obtained. The extracted cellulose was used to produce ethanol-gel with varying water content. The gel with properties closest to the SANS 448 standard contained 90 vol% ethanol and 10 vol% water, with 38 wt% cellulose. This gel was found to ignite readily and burn steadily, without flaring, sudden deflagrations, sparking, splitting, popping, dripping or exploding from ignition until it had burned to extinction, as required by SANS 448. The only specifications that could not be met were the viscosity (23,548 cP) and the high waste residue (32 wt%) left after burning. The other major concern is the extremely high costs involved with the manufacturing of ethanol-gel from water hyacinth cellulose. It can be concluded that ethanol-gel cannot be economically produced using water hyacinth as feedstock. Chemical and enzymatic extraction of water from the feedstock, which is stems and leaves or roots, showed that the highest yield of water was obtained using a combination of Celluclast 1.5 L, Pectinex Ultra SP-L and additional de-ionised water. A yield of 0.89 ± 0.01 gwater/gwater in biomass was realised. This is, however, only 0.86 wt% higher than the highest yield obtained (0.87 ± 0.01 gwater/gwater in biomass) using only Pectinex Ultra SP-L and de-ionised water. It is recommended to use only Pectinex Ultra SP-L and de-ionised water at a pH of 3.5 and a temperature of 40°C. Using one enzyme instead of two reduces operating costs and simplifies the chemical extraction process. The extracted water, both filtered and unfiltered, was not found to be suitable for domestic use without further purification to reduce the total dissolved solids (TDS), potassium and manganese levels. Both the unfiltered and filtered water were, however, found to be suitable for industrial and agricultural purposes, except for the high TDS levels. If the TDS and suspended particle level can be reduced, the extracted water would be suitable for domestic, industrial and agricultural use. The potential fermentation of the sugars derived from the water hyacinth, using ultrasonic pretreatment, was investigated. Indirect ultrasonic treatment (ultrasonic bath) proved to be a better pretreatment method than direct sonication (ultrasonic probe). The optimum sugar yield for the ultrasonic bath pretreatment with 5% NaOH was found to be 0.15 g sugar/g biomass (0.47 g sugar/g available sugar) using an indirect sonication energy input of 27 kJ/g biomass. The optimum sugar yield is lower than those reported in other studies using different pretreatment methods. Theoretically a maximum of 0.24 g ethanol can be obtained per g available sugar. This relates to an ethanol yield of 0.08 g ethanol/kg wet biomass. The low yield implies that ethanol production from water hyacinth is not economically feasible. The production of bio-oil and bio-char from water hyacinth through thermochemical liquefaction of wet hyacinth feedstock was investigated. An optimum bio-char yield of 0.55 g bio-char/g biomass was achieved using an inert atmosphere (nitrogen) at 260°C and the stems and leaves as feedstock. With the roots as feedstock a slightly lower optimum yield of 0.45 g bio-char/g biomass was found using a non-reducing atmosphere (carbon monoxide) at 280°C. The bio-oil yield was too low to accurately quantify. As water is required during thermochemical liquefaction, it was found unnecessary to dry the biomass to the same extent as was the case with the pretreatment and fermentation of the water hyacinth, making this a more feasible route for biofuel production. Bio-char produced through liquefaction of roots as the feedstock and leaves and stems as the other feedstock had a higher heating value (HHV) of 10.89 ± 0.45 MJ/kg and 23.31 ± 0.45 MJ/kg respectively. Liquefaction of water hyacinth biomass increased the HHV of the feedstock to a value comparable to that of low grade coal. This implies a possible use of water hyacinth for co-gasification. The most effective route for bio-energy production in the case of water hyacinth was found to be thermochemical liquefaction (12.8 MJ/kg wet biomass). Due to the high production costs involved, it is recommended to only use water hyacinth as a feedstock for biofuel production if no alternative feedstock are available. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2014