Abstract In this study, the removal of Pb(II) from aqueous solutions by tassel powder was studied and optimised. Batch experimentswere conducted on simulated solutions using tassel powder adsorbent and the effects of contact time, pH and concentration on the extent of Pb (II) removalwas studied. Equilibrium and kinetic models for Pb(II) sorption were developed by considering the effect of contact time and concentration at optimum pH 4 and fixed temperature(25 ◦C). The Freundlich model was found to describe the sorption energetics of Pb(II) on tassel more fully than the Langmuir. A maximum Pb(II) loading capacity of 333.3 mg/g on tassel was obtained. The adsorption process could be well described by both the Langmuir and Freundlich isotherms with R2 values of 0.957 and 0.972, respectively. The kinetic parameters were obtained by fitting data fromthe effect of contact time on adsorption capacity into the pseudo-first, pseudo-second-order and intra-particle diffusion equations. The kinetics of Pb(II) on tassel surface was well defined using linearity coefficients (R2) by pseudo-second-order (0.999), followed by pseudo-firstorder (0.795) and lastly intra-particle diffusion (0.6056), respectively. The developed method was then applied to environmental samples taken fromborehole waters contaminated with mine wastewater. The removal of Pb (ND-100%), Se (100%), Sr (5.41–59.0%),U(100%) and V (46.1–100%)was attained using tassel. The uptake of the metals from environmental samples was dependent on pH, ionic strength and levels of other competing species.

A b s t r a c t In this study, the removal of Pb(II) from aqueous solutions by tassel powder was studied and optimised. Batch experimentswere conducted on simulated solutions using tassel powder adsorbent and the effects of contact time, pH and concentration on the extent of Pb (II) removalwas studied. Equilibrium and kinetic models for Pb(II) sorption were developed by considering the effect of contact time and concentration at optimum pH 4 and fixed temperature(25 ◦C). The Freundlich model was found to describe the sorption energetics of Pb(II) on tassel more fully than the Langmuir. A maximum Pb(II) loading capacity of 333.3 mg/g on tassel was obtained. The adsorption process could be well described by both the Langmuir and Freundlich isotherms with R2 values of 0.957 and 0.972, respectively. The kinetic parameters were obtained by fitting data fromthe effect of contact time on adsorption capacity into the pseudo-first, pseudo-second-order and intra-particle diffusion equations. The kinetics of Pb(II) on tassel surface was well defined using linearity coefficients (R2) by pseudo-second-order (0.999), followed by pseudo-firstorder (0.795) and lastly intra-particle diffusion (0.6056), respectively. The developed method was then applied to environmental samples taken fromborehole waters contaminated with mine wastewater. The removal of Pb (ND-100%), Se (100%), Sr (5.41–59.0%),U(100%) and V (46.1–100%)was attained using tassel. The uptake of the metals from environmental samples was dependent on pH, ionic strength and levels of other competing species.

Conditions within maize (Zea mays L.) fields can cause plant-to-plant variability (PPV) because of emergence, spacing, and mid-season growth non-uniformities. PPV has been associated with yield reductions in maize. Maize growers can influence field conditions and maize yields through management practices such as rotation and tillage. The objectives of this research were to determine the effect that tillage and crop rotation systems have on maize growth and PPV, and whether PPV is a mechanism for yield differences observed among management systems. Field experiments were conducted at the Elora Research Station in Ontario, Canada in 2010 and 2011, where maize was grown under various tillage and rotation treatments. Plant-level measurements were taken throughout the season. Diverse crop rotations and conventional tillage (CT) increased grain yields. Maize grown in no-tillage (NT) treatments had later seedling emergence, lower leaf numbers throughout the season, shorter plants at silking, later anthesis and silking, and lower plant grain yields compared to CT treatments. Rotations that incorporated alfalfa or cover crops had earlier silking dates and fewer plants that were developmentally delayed compared to mono-crop rotations. PPV was characterized using variance (s2) and the coefficient of variation (CV), but the two approaches did not drastically change the outcome of the study. Tillage more consistently altered PPV than rotation treatments. NT had higher variability in emergence, leaf number, silking date, plant spacing, anthesis-silking interval, and harvest index than CT. Higher variability in emergence, early-season leaf number, dry matter at silking,and harvest index were found to be mechanisms for lower yields in NT treatments. This research suggests that producers should take measures to limit variability in these parameters due to their associations with yield reductions, especially when growing maize in NT systems.

No description available.

xx, 94 leaves : graphs, tables ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1980) from the Dept. of Agricultural Biochemistry, University of Adelaide

Maize (Zea mays L.) is a cereal crop grown throughout the world. It plays an important role in the diet of millions of African people due to its high yields per hectare, its ease of cultivation and adaptability to different areas, its versatile food uses and storage characteristics (Asiedu, 1989). Maize is a staple crop in Southern Africa where it accounts for 70% of total human intake of calories (Martin et al., 2000). Thus it is essential that maize can be sustainably produced in South Africa and that maize seeds are of the highest possible quality. Fungi rank as the second biggest cause of deterioration and loss of maize (Ominski et al., 1994). At the very early stages of seedling development, maize seedlings are attacked by fungi such as Pythium, Fusarium and Rhizoctonia spp., which cause severe diseases, including pre-emergence damping-off, which lead to yield losses (Dodd & White, 1999). These diseases can be effectively controlled by applying fungicidal seed treatments (Peltier et al., 2010). However, these seed treatments should be tested to ensure that they provide an acceptable level of control against the pathogens and that they do not have any negative effects on the germination and vigour of the maize seed. In Chapter 3 of this dissertation, three important fungal genera, namely Pythium, Fusarium and Rhizoctonia spp., were isolated from diseased maize plant samples and soil. The beet seed baiting method was used for Rhizoctonia sp. and the citrus leaf disk baiting method for Pythium sp. Fusarium sp. was isolated by means of serial dilution on a selective medium. The selective media used were agar containing chlorotetracycline hydrochloride and streptomycin sulfate for Rhizoctonia, pimaricin and vancomycin, PARP (pimaricin + ampicillin + rifampicin + pentachloronitrobenzene (PCNB) agar) for Pythium sp. and Rose Bengal Glyceraldehyde Urea (RBGU) for Fusarium sp. These fungal isolates, as well as some isolates revivedfrom the University of Pretoria’s culture collection and obtained from the Agricultural Research Council (ARC-PPRI), were used for pathogenicity trials conducted on maize in the between-paper method (BP), and in six-celled plastic seedling trays in the greenhouse (described in Chapter 5). In order to test the efficacy of Stamina, Flite and Celest® XL for controlling Pythium spp., Fusarium spp. and Rhizoctonia spp. in vitro, each of the three fungicides was added to PDA at concentrations of 1, 2 and 3ppm. In order to mirror the treatments used in other experiments, a combination of Stamina and Flite was also incorporatedinto PDA at concentrations of 1, 2 and 3ppm each. A 5mm2 block of each of the fungi was plated onto the centre of the media and incubated at 25C. The diameter of the fugal growth was measured at regular intervals depending on the rate of growth of the fungus. It was found that Celest® XL was very effective in controlling all three of these pathogens in vitro, confirming research done by Govender (2005), who found that Celest® XL effectively controlled these pathogens on maize. The combination of Stamina and Flite also controlled these pathogens although to a lesser extent. Research done by BASF in 2008 showed that Stamina is able to control Pythium, Fusarium and Rhizoctonia spp. Pyraclostrobin (the active ingredient of Stamina) has also been found to effectively control all three of these pathogens in numerous in vitro and in vivo experiments (Broders et al., 2007; Peltier et al., 2010; Solorzano & Malvick, 2011). In Chapter 4 of this dissertation, the effect of three different fungicides (Stamina, Flite and Celest® XL) on the germination and vigour of two Zea mays cultivars (Monsanto DKC78-15B and PANNAR 6Q308B) was assessed. This was achieved by carrying out a standard germination test, a cold soil test, short accelerated ageing and long-term storage tests according to the guidelines of the International Seed Testing Association (ISTA, 2012). It was found that none of the fungicides had a detrimental effect on either seed germination or vigour and no phytotoxic effects were observed. The combination of Stamina and Flite treatment also led to an increased percentage germination after the cold soil test when compared to the untreated control. This confirms the research of Govender (2005), who showed that Celest® XL had no negative effects on the germination or vigour of maize, and BASF (2008), which showed that Stamina could even lead to increased germination and an increased yield of maize under cold conditions when compared to an untreated control. Bradley et al. (2001) found that fungicide seed treatments do not affect the vigour and viability of maize seeds. Seeds treated with fludioxonil also showed an increased radicle length in some cases (Munkvold & O’Mara, 2002). Increased radicle length could indicate increased vigour of the seeds (Matthews & Khajeh-Hosseini,2006). / Dissertation (MSc (Agric))--University of Pretoria, 2013. / Microbiology and Plant Pathology / MSc (Agric) / Unrestricted

Philosophiae Doctor - PhD / Mycotoxins attract worldwide attention because of the significant economic losses associated with their impact on human health, animal productivity, domestic and international trade. Over 300 mycotoxins have been discovered, of which a few are of serious concern (Smith and Moss 1985; Rheeder et al., 1994). Exposure to these mycotoxins can produce both acute and chronic effects ranging from death to effects upon the central nervous, cardiovascular, pulmonary systems and upon the alimentary tract. Mycotoxins may be carcinogenic, mutagenic, teratogenic and immunosuppressive (Ferrante et al., 2002). Mycotoxins are currently considered as a major problem in developing countries (Miller, 1994).

Aflatoxins are a secondary metabolite produced by the fungus Aspergillus flavus. A. flavus has been known to infect several crops including tree nuts, peanuts, rice, cotton and maize. Aflatoxins have been found to cause tumors with aflatoxin B1 being the most carcinogenic biologically produced substance known to man. Therefore, the FDA has restricted the amount of aflatoxin in maize for human consumption to 20 ppb (ng/g). An estimated $225 million are lost each year in the United States due to aflatoxin contamination in maize crops alone. Agriculture is a vital part of Mississippi’s economy, and maize is one of its largest crops. The purpose of this research is to track the correlations between aflatoxin accumulation and Aspergillus flavus fungal biomass for the first several weeks after inoculation, as well as the spreading of the fungus and the aflatoxin throughout the inoculated ear of maize. This will allow for better understanding of the pathogen-host interactions and how the fungus progresses over time. GA209 x T173 is the aflatoxin accumulation susceptible maize hybrid, GA209 x Mp313E is the susceptible and resistant hybrid, and Mp717 x Mp313E is the resistant maize hybrid to aflatoxin accumulation. These maize hybrids were each inoculated with toxin producing Aspergillus flavus NRRL 3357 and water as a control 21 days after silk maturation. Collections of the inoculated maize cobs were made 3, 7, 14, 21, 28, 35, and 60 days after inoculation. Maize samples were collected and analyzed for aflatoxin and DNA concentration. The extracted aflatoxin was analyzed using an LC/MS. The fungal biomass was determined by performing quantitative real time polymerase chain reaction (PCR). GA209xT173 and Mp717xMp313E showed no aflatoxin production two days after inoculation. The resistant maize hybrid lead in aflatoxin accumulation the last two years but had the least amount of fungal biomass for second and third years of the experiment The production of aflatoxin seems to begin decelerating after 21 days after inoculation. Resistance characteristics are more to prevent fungal infection. Fungal biomass was significantly higher in the susceptible hybrid GA209xT173 compared to the other hybrids. However, fungal spread was significantly higher in Mp313ExT173 and Mp717xMp313E.

No description available.

To determine the limiting factors in nitrate assimilation in maize and barley, the effects of nitrate on 1) steady state levels of nitrate reductase activity (NRA) and nitrate reductase protein (NRP); 2) the uptake, translocation and accumulation of nitrate in the shoots of the seedling plant were examined. Seedlings were grown on Kimpack paper containing l, 5 or 20mM KN0₃ for 7 days at 20°c (barley) or 28°C (maize). At lmM KN0₃ the rate of 3 nitrate uptake and the levels of NRA and NRP were higher in maize than in barley. In contrast., at 5 and 20mlv1 KNo₃, the rate of uptake, the accumulation of nitrate and the NRA were higher in barley than in maize. The results suggest that the synthesis of NR is induced by lower levels of nitrate in maize relative to barley. In addition, nitrate-nitrogen appears to be more efficiently converted to proteins, other than NR, in maize than in barley. At very low levels of nitrate an inactive NR protein was present. in maize. To characterize the inactive NR, maize plants were grown under conditions where high levels of NRA were detected (vermiculite:sand, l:lw/w, containing 10mM KN0₃) and under conditions where NR was present primarily in the inactive form (Kimpack paper:washed sand). Nitrate reductase was purified from primary leaves using Blue Sepharose affinity chromatography. The column was washed with NADH and KN0₃ in each case. The peaks of NR were 3 detected using Dot-immunoblotting, with an antibody prepared against maize leaf NR and by assessing the NRA. Active and inactive NR forms were found both at the NADH-and the KN0₃-wash. In the NADH-wash, the inactive NR as compared to the active form, has very low NADH (complete), FMNH₂, MV and BPB (reductase) activities. Significant levels of cyt-c and FeCN (dehydrogenase) partial activities were detected. Similarly, the inactive NR in the KN0-wash, had 3no NADH (complete), FMNH2 , MV and BPB (reductase) activities. Very low levels of cyt-c and FeCN (dehydrogenase) NR partial activities were detected, compared to the respective activities of the active enzyme in the KNO₃ wash. / Thesis / Master of Science (MSc)