School of Life Sciences

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Alleviating delayed field curing-induced deterioration in rice seeds by cathodic water invigoration: a comparison of seed and seedling responses in two upland rice species and their interspecific hybrid.
(2021) Bam, Raphael Kwame.; Varghese, Boby.; Naidoo, Sershen.; Pammenter, Norman William.
Rice constitutes the major source of the world’s food supply. A number of varieties are grown in many parts of the world, all which produce orthodox seeds that are usually stored between growing seasons. As in other crop species, storage-induced loss of seed quality (viability and vigour) is inevitable but considerable research effort has been invested in optimising seed bank storage protocols for rice to ensure acceptably high levels of seed germinability and seedling emergence. However, poor post-harvest practices such as delayed field curing before threshing in developing countries in the humid tropics, such as Ghana, result in curing-induced seed deterioration in the field prior to ex situ storage. Given that many rice growing regions are likely to experience significant levels of climate change, seed processing and storage induced declines in rice seed quality could exacerbate the crop losses incurred by rice farmers in these regions in the future. This motivated the present study which was designed around three aims: 1) to investigate how environmental conditions and the duration of field curing influenced seed macro-structural integrity, susceptibility to microbial infection, and seed germinability and vigour; 2) to identify macro-structural and ultrastructural indicators/ biomarkers of field curing and associated storage-induced stress/ damage; 3) to assess whether the invigoration of field-cured seeds with cathodic water (CW), an established antioxidant-based seed invigoration medium, and deionized water (DW) can alleviate the deteriorative effects of delayed field curing on rice seed cellular integrity, germination and subsequent seedling growth and biomass. The specific objectives of this comparative study, which involved an Asian (Oryza sativa L.) and African (Oryza glaberrima Steud) upland rice species and their interspecific hybrid (O. sativa × O. glaberrima), were as follows: a) to compare the impacts of delayed field curing in wet and dry environments on seed physical, physiological and pathological quality; b) to identify potential ultrastructural biomarkers of seed sensitivity to delayed field curing-induced stress/ damage in embryonic root meristematic cells using transmission electron microscopy (TEM); c) to assess whether CW invigoration alleviates cellular stress/ damage induced by delayed field curing using selected ultrastructural biomarkers of seed sensitivity to such curing-induced stress/ damage; and d) to assess whether invigoration with CW and DW improves seed germinability and emergence, and subsequent plant growth in field cured seeds, relative to non-invigorated (NI) dry seeds.
Bioeconomic feasibility of aquaponics in South Africa: leapfrogging for sustainable development of freshwater aquaculture.
(2020) Adeleke, Babatunde Ayoade.; Robertson-Andersson, Deborah Vivienne.; Moodley, Ganas Kandasamy.; Taylor, Simone.
Food security is being threatened globally due to a combination of factors, such as climate change, anthropogenic pressures and burgeoning competition for limited water and land resources. The need to adopt environmentally and economically sound sustainable food production systems which are adaptable to the prevailing environmental stressors is imperative. Aquaponics sustainably converts aquaculture waste into nutrients for plant uptake resulting in an unconventional food production system which potentially provides an economically viable means of food production. Integrated recirculating aquaculture as adaptive technology is complex and capital intensive, thus, must be financially sustainable. This study, therefore, assessed the bioeconomic feasibility of aquaponics (a branch of aquaculture) in South Africa as a potential leapfrog technology for the rapid development of aquaculture, attainment of food security and local economic development. Quantitative and qualitative SWOT analyses, and key success factors of leading aquaculture players in Africa (Egypt, Nigeria and Uganda) were used as a benchmark to assess the South African aquaculture sector. Qualitative analysis of South African aquaculture sector vis-à-vis the leading aquaculture players in Africa reveals a suboptimal environment that is not suitable to drive costeffective and competitive conventional large-scale commercial aquaculture. Also, inadequate enabling environment due to bureaucratic hindrances towards the implementation of well-crafted aquaculture development policies and framework, and higher operating cost were identified. The quantitative SWOT analysis of key aquaculture players in Africa revealed Egypt was having the highest aquaculture development competitive strengths, and Nigeria showed the highest aquaculture development and market opportunities. Quantitative SWOT analysis of key aquaculture species in South Africa showed trout and tilapia have the highest competitive strengths, while abalone, oyster and marron crayfish showed good market opportunities but weak in competitive strengths. Growth performance of Oreochromis mossambicus and the yields from plants – tomato, pepper and cucumber due to the effects of plant density and stem pruning were assessed in a twin system designed, constructed and operationalized as a low-cost, small-scale aquaponic system. The economic viability of the aquaponic system was assessed using the price trend analysis of fresh produce in South Africa, biomass yield, cost inputs and revenue models using conventional aquaponic cultural methods. Financial performance was determined using financial metrics such as return on investment (ROI), net present value (NPV), internal rate of return (IRR) and profitability. Analyses were modelled to determine the financial performance of the aquaponic system. The growth performance and yield of fish cultured in the aquaponic system showed excellent performance based on FCR (1.25 %), survival rate (97.5 %), LWR r2 (0.945), regression coefficient b (3.1) and condition factor K (1.93). Total and marketable yield of vegetables (tomato, sweet pepper and cucumber) significantly increased (p < 0.05) with a higher plant density of 8 plants /m2 compared to 5 plants/m2. Plants with a higher stem pruning to two and three stems performed significantly better than those pruned to one stem (p < 0.05). The interactive effects of a higher plant density and stem pruning resulted in significant (p < 0.05) higher total and marketable yields with all the plants. Economic analysis of the small-scale aquaponic setup and operation did not present economic feasibility with the adoption of conventional cultural techniques (a revenue model of 59: Abstract 41 % fish to plant ratio) as a result of the higher operating cost associated with fish production. A fish to plant revenue model of 42 : 58 % ratio (achieved by adopting optimized cultural technique) however, showed marginal economic viability. Plant yield in aquaponics can be improved for higher economic returns through the synergistic optimization of plant density and stem pruning while adopting other optimal cultural management practices. A minimum revenue model of 30 : 70 % fish to plant ratio is recommended for aquaponic operations in South Africa to attain economic feasibility. Aquaponics thus presents optimistic potential to drive sustainable and feasible food production in South Africa with the adoption of viable production and marketing strategies.
Cathodic water invigoration of deteriorated orthodox seeds – implications on subsequent plant growth.
(2020) Fatokun, Kayode.; Beckett, Pichard Peter.; Varghese, Boby.; Pammenter, Norman William.
Orthodox seeds deteriorate even when kept under the best of conditions leading to loss of germination, poor seedling growth. In this study, a novel approach via the use of cathodic water, an electrolysed form of calcium magnesium solution, was used to invigorate fresh and controlled deteriorated seeds of wild (Bolusanthus speciosus (Bolus) Harms, Combretum erythrophyllum (Burch.) Sond., Erythrina caffra Thumb.) and agricultural (Pisum sativum L., Cucurbita pepo L.) species. Other treatment solutions investigated alongside cathodic water were un-electrolysed calcium-magnesium solution and deionized water. Fresh seeds of the test species were controlled deteriorated to 50% germination (P50) at 40°C and 100% relative humidity. Thereafter, the seeds were invigorated with the treatment solutions. Fresh and un-primed controlled deteriorated seeds served as the control. In addition, to study the mechanism of invigoration, the effects of priming on the membrane stability index (MSI), amylase activities, lipid peroxidation products malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) were investigated. The effects of priming on the reactive oxygen species (ROS) scavenging enzymes superoxide dismutase, and catalase and DNA (concentration and purity). All priming treatments improved germination, emergence, growth parameters and subsequent seedling photosynthesis relative to the unprimed seeds. In general, cathodic water was most effective at invigorating seeds in the all test species. Also, controlled deteriorated seeds benefitted more than the fresh seeds treatments. Analyses of the lipid peroxidation products and antioxidant enzyme activities in invigorated seeds provided support for the hypothesis that the effectiveness of cathodic water in the invigoration of debilitated orthodox seeds derive from its ability to act as a potent antioxidant. This study, which is a novel approach at bringing the concept of electrochemistry into germplasm conservation via the use of cathodic water, has also confirmed the efficacy of cathodic water in invigorating debilitated seeds. This is especially critical for seeds containing traits that may be under the threat of being lost due to various reasons. The current study reinforces the strong potential of cathodic water in the recovery of aged germplasm and improved yield of orthodox seeded species.
Designing T-cell epitope-based vaccine against Eimeria infection in chicken using immunoinformatics approach.
(2021) Madlala, Thabile.; Adeleke, Matthew Adekunle.; Okpeku, Moses.
Chicken coccidiosis is the most significant ubiquitous, intestinal parasitic disease known to infect chickens globally. It is recognised for incurring significant production loss to the poultry industry, caused by single or multiple Eimeria spp. infections which threaten chicken welfare and productivity. The emergence of drug resistance in parasites and pathogenicity reversion has put pressure on the poultry industry to reduce chemoprophylactic drugs and live vaccines as preventive measures against coccidiosis. Recombinant DNA vaccines have shown promising results as an alternative option, but complete protection has not been reported highlighting the need for the design of new vaccine against this disease. In this study, Eimeria antigens Immune Mapped Protein-1(IMP1) and Microneme Protein-2(MIC2) were explored using reverse vaccinology and immunoinformatics tool to predict and design potential multiepitope vaccine candidate against coccidiosis. A total of 28 and 19 antigenic T-cell epitopes were predicted and used to construct two multiepitope vaccines with 610 and 512 amino acids for IMP1 and MIC2, respectively. The produced vaccines exhibited favoured characteristics for an ideal vaccine candidate; they were antigenic (Vaxijen score of 0.5989 and 0.5103), immunogenic (scores: 10.15 and 9 419), thermostable (instability index <40 ), and non-allergic. The presence of IFN-gamma and IL-4 inducing epitopes in the constructed vaccine enables vaccine to trigger a cellular and humoral response within the host. Molecular docking of designed vaccines with toll-like receptors (TLR4 and TLR5) to determine vaccine interaction and stability was confirmed by molecular dynamics simulation root-mean square deviation (RMDS) and root-mean-square fluctuation (RMSF) analysis. The designed vaccines induced immune response through production of cytokines and antibodies associated with tertiary response. When exposed to online immune simulation C-ImmSim, both vaccines produced potent immune response through production of IgG, Tc and Th cell and memory Bcells. The constructed multiepitope vaccine in this present study is highly promising and as such further experimental work should be done to confirm its suitability against chicken coccidiosis.
Diversity of Eimeria tenella apical membrane antigen-1 from chickens in Mpumalanga province and its in silico epitope prediction as a vaccine candidate.
(2021) Tenza, Petronella Nokukhanya.; Adeleke, Matthew Adekunle.; Fatoba, Abiodun Joseph.
Coccidiosis has been a significant challenge in the poultry industry. There is a high request for the modification of a cost-effective immunizing agent to curtail this disease. Apical membrane antigen 1 (AMA1) has been reported as a protective antigen in sub-unit vaccine development against several apicomplexan parasites such as Plasmodium falciparum, Eimeria tenella and Eimeria maxima. However, knowledge of genetic diversity in this vaccine candidate is imperative. Also, to minimize the cost and time involved in producing a vaccine, computational vaccine design has received much attention through the immunoinformatics method. Therefore, screening for the potential vaccine epitopes in AMA1 that can induce cellular and humoral immune response through the immunoinformatics technique looks promising. This investigation aimed to detect the level of genetic diversity amid Eimeria tenella Apical Membrane Antigen 1(EtAMA1) in selected farms in Mpumalanga province and predict vaccine epitopes from this antigen. Four hundred fresh faecal samples were collected from 10 selected broiler chicken farms in Mpumalanga. The samples were screened for Eimeria oocyst using a compound microscope, and samples containing oocyst were further screened for E. tenella using molecular methods. AMA1 (n=103) was amplified from positive samples for E. tenella, and resulted amplicons were sent to Inqaba Biotec for sequencing and analyzed using MEGA6.06 and DnaSP programs. The results revealed low levels of genetic diversity among Mpumalanga EtAMA1 sequences which were measured by nucleotide diversity (0.0007) diversity, haplotype diversity (0.113) and haplotype number (3). Correspondingly, the haplotype network revealed 4 haplotypes, 3 of which consist of samples from Mpumalanga. Identification of immunogenic B- and T-cell epitopes from EtAMA1 sequences was further carried out and were used to construct a multiepitope vaccine (MEV) using immunoinformatics approaches. The constructed MEV is 311 amino acids long. It was constructed by linking 6 B-cell, 3 CD8+ epitopes and 6 CD4+ epitopes with appropriate adjuvant and linkers. Both adjuvant and linkers were used to increase the immunogenicity of the MEV. The designed MEV was highly antigenic and non-allergenic. The results showed a strong binding affinity of MEV with TLR4. These results suggest that the predicted vaccine could be a significant vaccine candidate against chicken coccidiosis through further experimental validation is still necessary.
Optimization of antifungal production by Bacillus species in the presence of nanoparticle supplementation and preliminary scale-up.
(2023) Nzimande, Sikhulile Nosimo.; Gueguim Kana, Evariste Bosco.; Ramchuran, Santosh Omrajah.; Sanusi, Adeyemi Isaac.
The intensive agricultural practices used to meet global crop production demands have resulted in the rigorous use of chemical pesticides. These ultimately compromise crop production as well as the environment. In order to alleviate this, cheaper and environmentally friendly, biocontrol agents have been considered as an alternative to chemical pesticides. Biosurfactants are a promising alternative to chemical pesticides due to their higher biodegradability, lower toxicity, and environmental friendliness. Amongst the many bacterial and fungal biosurfactant producers, biosurfactants from Bacillus species show promise as biocontrol agents. These biosurfactants are known for their wide biotechnological use in agricultural, industrial, and medicinal fields. However, large scale production is still faced with challenges such as low yields and high production cost thus raising the need for modelling, optimization, catalytic and scale up investigations. Hence, a study was undertaken with the aim of enhancing biosurfactant production through process modelling and optimization with subsequent assessment of the scale up potential of the optimized process. A Response Surface Methodology (RSM) using box Behnken design was used to investigate the optimal process conditions for improved biosurfactant production from B. subtilis BS20. The investigated process parameters included glucose concentration (10 – 30 g/L), incubation temperature (25 – 45℃) and incubation time (24 – 96 h). The developed model gave a high coefficient of determination (R2 ) = 0.86, p-value of 0.0279 and F-value of 4.62 for the modelled biosurfactant production. Optimized process conditions of 11.5 g/L glucose concentration, 24 h incubation time and 41o C for incubation temperature were obtained and produced a maximal antifungal activity of 68 mm. Moreover, supplementary inclusion of seven (7) different nanoparticles as a biocatalyst in the cultivation of B. subtilis BS20 was carried out using the optimal process condition to further improve antifungal (biosurfactant) production. The inclusion of nanoparticles favored increased biomass yield, but biosurfactant with high antifungal activity was not obtained. Moreover, when it comes to commercializing new bioprocess and bioproduct developments, bio – process scale-up in the biotechnology industry is an essential stage. This study therefore evaluated the scale up of biosurfactant production based on constant power consumption, Reynold number and impeller tip speed. The stirrer speed (n), impeller diameter (di), number of impellers (N), power number (Np), broth density (⍴), working volume and geometric factor (fc) were correlated with impeller tip speed (Vtip), Reynolds number (𝑅𝑅𝑅𝑅) and power consumption rate (P/V) to obtain the most suitable criterion for biosurfactant production in a 10 L bioreactor. Implementing constant Vtip value from the 1 L scale: 93 rpm, Reynold number (Re) 5.9E - 04, Power (P) 0.32 W, Power to Volume ratio (P/VL) 160 W/m3 , circulation time (tc) 5.2 s and shear stress (γ) 15.5 S-1, at 41 °C, gave the highest antifungal activity of 65 mm zone of inhibition in the 10 L scale bioreactor. The antifungal activity obtained for constant Vtip were comparable to those obtained at 1L bioreactors (57 mm), this showed that the bioprocess dynamics for achieving high antifungal activity are available, further paving the way for feasible commercialization strategies. This study has elucidated the optimum process conditions for B. subtilis BS20 metabolism for improved biosurfactant production resulting in significant antifungal activity. Furthermore, findings showed that the inclusion of nanoparticles biocatalyst to the process enhanced biomass yields. Process scale up provided preliminary data for large scale production of biosurfactant production from B. subtilis BS20.
Physiological and biochemical investigations into the reinvigoration of deteriorated Brassica oleracea L. (Cabbage) and Lactuca sativa L. (Lettuce) seeds with antioxidants and inorganic salt solutions.
(2021) Adetunji, Ademola Emmanuel.; Varghese, Boby.; Naidoo, Sershen.; Pammenter, Norman William.
This study focused on reinvigorating deteriorated Brassica oleracea L. (cabbage) and Lactuca sativa L. (lettuce) seeds with antioxidants and inorganic (electrolysed and non-electrolysed) salt solutions. All pre-treatment solutions were applied to fresh (control) and controlled deteriorated (CDd) seeds at 75% viability (P75), 50% viability (P50) and 25% viability (P25). The pre-hydration treatments were compared in terms of their effects on seed germination, seedling vigour, electrolyte conductivity (EC), accumulation of lipid peroxidation products, protein carbonylation (PC), antioxidant enzymes and germination enzymes. The study also investigated the effects of invigorating CDd seeds with selected antioxidants on subsequent seedling growth, gas exchange and photochemistry under greenhouse conditions. Controlled deterioration, in general, resulted in the loss of seed vigour and viability but at higher rates in lettuce than cabbage, and increased EC and PC, and lowered antioxidant and germination enzymes activities in both species. However, significant lipid peroxidation was only recorded in lettuce seeds. Antioxidant pre-treatments enhanced viability of CDd seeds of cabbage at P25 and lettuce at P50 and P25, and improved seedling vigour of fresh, P75 and P50 cabbage, and P50 and P25 lettuce seeds. Antioxidant pretreatments reduced EC and lipid peroxidation in lettuce seeds, while PC was reduced in both species. The treatments also elevated antioxidant and germination enzymes activities in P25 cabbage seeds and P50 and P25 lettuce seeds. The inorganic salt pre-treatments did not enhance percentage seedling production in CDd cabbage seeds. However, in CDd lettuce seeds, Cacontaining solutions and electolysed (cathodic water) treatments promoted percentage normal seedling production and enhanced seedling vigour irrespective of pre-treatment solution pH or seed deterioration level. In the greenhouse studies, certain antioxidants promoted seedling vigour and leaf area in both species and enhanced shoot dry weight and gas exchange in lettuce. In summary, CDd lettuce seeds responded better to both types of invigoration (i.e., antioxidants and inorganic salt solutions) than cabbage seeds, while antioxidants appeared to be relatively more beneficial than inorganic salts in both species. The results suggest that the benefits of certain pre-treatment solutions were based on the enhancement of the activities of key antioxidant and germination enzymes, and the efficiency of photosynthesis at the early stages of growth. The results argue for the use of these seed pre-hydration treatments for mitigating poor stand establishment brought about by seed ageing, and as a useful approach to reinvigorating seeds in long-term storage collections for ensuring global food security.
Responses to chilling and cryopreservation of recalcitrant seeds of Ekebergia capensis from different provenances.
(2020) Bharuth, Vishal Behary Lal.; Beckett, Richard Peter.; Pammenter, Norman William.
Recalcitrant seeds are shed at relatively high water contents and are metabolically active. The effect of chilling the recalcitrant seeds of purportedly a single species, Ekebergia capensis, from Port Elizabeth (PE; Eastern Cape), St Lucia (KwaZulu-Natal [KZN]) and Tanzania (tropical southern Africa) was tested. Viability and axis ultrastructure, solute leakage and protein synthesis were investigated. Additionally, cryopreservation of embryonic axes (explants) was studied. In particular, the ability of cathodic water to improve explant survival was tested, and related to its effect on the production of potential harmful reactive oxygen species such as superoxide (·O2-) and hydrogen peroxide (H2O2), and its ability to maintain levels of total aqueous antioxidants (TAA). Shoot and root ultrastructure were examined after each cryopreparative step in explants treated with and without cathodic water, and ultrastructure correlated with survival. The seeds from PE retained 80% viability after 12 weeks storage at 1° and 3°C and 100% when stored at 6°C. Those from St Lucia were dead after 38 d storage at 3°C. All the seeds from Tanzania were dead after 9 d when stored at 3°C. The rate of protein synthesis decreased gradually over the storage period, irrespective of the provenance. Electrolyte leakage from axes showed that those from St Lucia and Tanzania ‘leaked’ solutes irrespective of the duration or temperature or storage, but those from PE showed an initial increase, which then decreased. A 30% mass loss was achieved after 48 d, 230 h and 21 h for seeds from PE, St Lucia and Tanzania, respectively. Nuclear ribosomal ITS1 sequences revealed the presence of three well-to-strongly-supported monophyletic clades corresponding to the geographical areas from which the seeds were sampled (PE, KZN and Tanzania). Axes from the seeds from St Lucia and Tanzania lost ultrastructural integrity during storage while those from PE did not. The levels of ·O2- and H2O2 increased gradually after each cryopreparative step. Using cathodic water allowed 30% of PE explants to survive cryopreservation, while none of the St Lucia explants did. Root ultrastructure was well preserved, however, gradual ultrastructural deterioration was observed in the shoot meristem.

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