Effects of greywater irrigation on germination, growth and photosynthetic characteristics in selected African leafy vegetables

The reuse of greywater, wastewater from sources other than toilets, could enable low-income  households to save potable water for drinking and cooking. Greywater irrigation of food crops is widely practised but its effects on African leafy vegetables (ALVs), which hold potential for cultivation to improve food security, are unknown. This study investigated the effects of synthetic greywater  irrigation on germination in three ALVs, viz., Amaranthus dubius, Cleome gynandra and Solanum nigrum, and subsequent seedling growth in A. dubius and S. nigrum. Seeds and seedlings were treated with chlorinated and dechlorinated greywater and tap water, supplemented with nutrients. Greywater application decreased germination capacity (by 23–25%) when assessed in Petri dishes in A. dubius only. However, greywater application was less harmful to A. dubius seeds sown in soil. Vigour was compromised in greywater-treated seeds of all three species but greywater can be used to irrigate freshly-sown seeds of A. dubius without reducing percentage seedling production. However, greywater irrigation reduced capacity (by 21–23%) and rate of shoot emergence in S. nigrum, and growth and chlorophyll content in both species. These negative effects were accompanied by increased soil  electrical conductivity (after 21 d) and pH (after 14 d). The reduced growth under greywater irrigation was most likely based on a reduction in light-harvesting capacity and/or nutrient availability. Overall, S. nigrum seedlings were significantly more sensitive to the negative effects of greywater, possibly due to increased transpirational water loss under greywater irrigation. The effects of greywater were largely independent of chlorine content. Applying greywater in excess of plant requirements and/or alternating greywater irrigation events with freshwater watering events could promote leaching of salts found in greywater. The effects of greywater irrigation on soil water and nutrient availability demand further investigation for ALVs.Keywords: African leafy vegetables, greywater irrigation, germination, seedling growt

Studies on factors influencing viability after cryopreservation of excised zygotic embryos from recalcitrant seeds of two amaryllid species.

Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2010.Recalcitrant unlike orthodox seeds do not show a sharp border between maturation and germination and remain highly hydrated and desiccation-sensitive at all developmental and post-harvest stages. In contrast with recalcitrant seeds, orthodox types retain viability for predictably long periods in the dry state and hence can be stored under low relative humidity and temperature conditions. Storage of recalcitrant seeds under conditions allowing little to no water loss, at moderate temperatures, allows for short- to medium-term storage but only facilitates viability retention for a matter of a few weeks to months, at best, because the seeds are metabolically active and initiate germination while stored. Cryopreservation, i.e. storage at ultra-low temperatures (usually in liquid nitrogen [LN] at -196°C), is a promising option for the long-term germplasm conservation of recalcitrant-seeded species but their seeds present some unavoidable difficulties in terms of the amenability of their germplasm to cryopreservation. Pre-conditioning treatments can reduce the amount of ‘free’ water available for freezing and may increase the chances of cells or tissues surviving exposure to cryogenic temperatures. Such conditioning may be imposed by physical dehydration or cryoprotection, i.e. exposure to compounds that depress the kinetic freezing point of water and so reduce the likelihood of lethal ice-crystal formation during cooling (i.e. exposure to LN at -196°C or sub-cooled LN at -210°C) and subsequent thawing. Partial dehydration is presently a standard pre-treatment for the cryopreservation of recalcitrant zygotic germplasm and explant cryoprotection has been shown to improve postthaw survival in some recalcitrant-seeded species. However, there is a paucity of information on the physiological and biochemical basis of post-thaw survival or death in recalcitrant seeds, and this is the major focus of the current contribution. Additionally, in light of the lack of understanding on how cryo-related stresses imposed at the embryonic stage are translated or manifested during subsequent seedling growth, this study also investigated the effects of partial dehydration and the combination of partial dehydration and cooling of recalcitrant zygotic embryos on subsequent in and ex vitro seedling vigour. All studies were undertaken on the zygotic embryos of two recalcitrant-seeded members of the Amaryllidaceae, viz. Amaryllis belladonna (L.) and Haemanthus montanus (Baker); both of which are indigenous to South Africa. Studies described in Chapter 2 aimed to interpret the interactive effects of partial dehydration (rapidly to water contents > and <0.4 g g-1), cryoprotection (with sucrose [Suc; nonpenetrative] or glycerol [Gly; penetrative]) and cooling rate (rapid and slow) on subsequent zygotic embryo vigour and viability, using three stress markers: electrolyte leakage (an indicator of membrane integrity); spectrophotometric assessment of tetrazolium chloride-reduction (an indicator of respiratory competence); and rate of protein synthesis (an indicator of biochemical competence). These studies showed that in recalcitrant A. belladonna and H. montanus zygotic embryos, stresses and lesions, metabolic and physical, induced at each stage of the cryopreservation protocol appear to be compounded, thus pre-disposing the tissues to further damage and/or viability loss with the progression of each step. Maximum post-thaw viability retention in both species appeared to be based on the balance between desiccation damage and freezing stress, and the mitigation of both of these via Gly cryoprotection. Post-thaw viabilities in both species were best when Gly cryoprotected + partially dried zygotic embryos were rapidly, as opposed to slowly, cooled. However, the rate at which water could be removed during rapid drying was higher in A. belladonna and this may explain why the optimum water content range for post-thaw survival was 0.40 g g-¹ for H. montanus. These results suggest that to optimise cryopreservation protocols for recalcitrant zygotic germplasm, attention must be paid to pre-cooling dehydration stress, which appears to be the product of both the ‘intensity’ and ‘duration’ of the stress. Cryoprotection and dehydration increased the chances of post-thaw survival in A. belladonna and H. montanus zygotic embryos. However, transmission electron microscopy studies on the root meristematic cells from the radicals of these embryos (described in Chapter 3) suggest that their practical benefits appear to have been realised only when damage to the sub-cellular matrix was minimised: when (a) pre-conditioning involved the combination of cryoprotection and partial dehydration; (b) the cryoprotectant was penetrating (Gly) as opposed to non-penetrating (Suc); and (c) embryos were rapidly cooled at water contents that minimised both dehydration and freezing damage. The ability of A. belladonna and H. montanus embryos to tolerate the various components of cryopreservation in relation to changes in extracellular superoxide (.O2 -) production and lipid peroxidation (a popular ‘marker’ for oxidative stress) was investigated in studies featured in Chapter 4. Pre-conditioning and freeze-thawing led to an increase in oxidative stress and the accompanying decline in viability suggests that oxidative stress was a major component of cryoinjury in the embryos presently investigated. Post-thaw viability retention in Gly cryoprotected + partially dried embryos was significantly higher than noncryoprotected + partially dried embryos, possibly due to the relatively lower post-drying lipid peroxidation levels and relatively higher post-drying and post-thawing enzymic antioxidant activities in the former. Exposure of certain plant tissues to low levels of oxidative or osmotic stress can improve their tolerance to a wide range of stresses. In contrast, exposure of H. montanus zygotic embryos to low levels of oxidative stress provoked by exogenously applied hydrogen peroxide (H2O2) or exposure of A. belladonna embryos to low levels of osmotic stress provoked by low water potential mannitol and polyethylene glycol solutions (in studies featured in Chapter 5) increased their sensitivity to subsequent dehydration and freeze-thaw stresses. Exposure of Gly cryoprotected and non-cryoprotected amaryllid embryos to such stress acclimation treatments may pre-dispose A. belladonna and H. montanus embryos to greater post-drying and post-thaw total antioxidant and viability loss than untreated embryos. To assess the vigour of seedlings recovered from partially dried H. montanus embryos, seedlings recovered from fresh (F) and partially dried (D) embryos in vitro were hardened-off ex vitro, and subsequently subjected to either 42 days of watering or 42 days of water deficit (in studies described in Chapter 6). In a subsequent study (described in Chapter 7), seedlings recovered from fresh (F), partially dried (D) and cryopreserved (C) A. belladonna embryos were regenerated in vitro, hardened-off ex vitro and then exposed to 12 days of watering (W) or 8 days of water stress (S) followed by 3 days of re-watering. Results of these studies suggest that the metabolic and ultrastructural lesions inflicted on A. belladonna and H. montanus zygotic embryos during cryopreservation may compromise the vigour (e.g. development of persistent low leaf water and pressure potentials and reduced photosynthetic rates) and drought tolerance of recovered seedlings, compared with seedlings recovered from fresh embryos. While the adverse effects of freeze-thawing were carried through to the early ex vitro stage, certain adverse effects of partial drying were reversed during ex vitro growth (e.g. the increased relative growth rate of seedlings from partially dried embryos). The reduced vigour and drought tolerance of seedlings recovered from partially dried and cryopreserved embryos in the present work may therefore disappear with an extension in the period afforded to them for hardening-off under green-house conditions, and in the field. The results presented in this thesis reinforce the notion that each successive manipulation involved in the cryopreservation of recalcitrant zygotic germplasm has the potential to inflict damage on tissues and post-thaw survival in such germplasm relies on the minimisation of structural and metabolic damage at each of the procedural steps involved in their cryopreservation. The results also highlight the need to design research programmes aimed not only at developing protocols for cryopreservation of plant genetic resources, but also at elucidating and understanding the fundamental basis of both successes and failures

Effects of exogenous application of five antioxidants on vigour, viability, oxidative metabolism and germination enzymes in aged cabbage and lettuce seeds

Ageing induces modifications capable of compromising seed vigour and viability. This study investigated the effects of exogenous application of five antioxidants: ascorbic acid (AA), gallic acid (GA), reduced glutathione (GSH), trolox and glycerol, on physical and biochemical lesions induced by controlled deterioration (CD) in Brassica oleracea (cabbage) and Lactuca sativa (lettuce) seeds. The antioxidants were applied at 0.2, 0.4 and 0.6 mM to fresh seeds and seeds subjected to CD: 75% viability (P75), 50% viability (P50) and 25% viability (P25); deionised water (DW) served as control. Controlled deterioration resulted in more abnormal seedlings production in cabbage than in lettuce seeds. Additionally, CD increased electrical conductivity (EC) and protein carbonylation (PC), lowered antioxidant and germination enzymes activities in both species but increased lipid peroxidation in lettuce seeds only. Exogenous application of antioxidants enhanced seed viability of cabbage at P25 and lettuce at P50 and P25; seedling vigour of fresh, P75 and P25 cabbage; P50 and P25 lettuce seeds. Electrolyte conductivity and lipid peroxidation were reduced by AA, GA, glycerol, GSH and trolox in lettuce seeds, while PC was reduced by GA, glycerol and GSH in both species

Pineapple stem-derived bromelain based priming improves pepper seed protein reserve mobilization, germination, emergence and plant growth

Pepper seeds are slow to germinate and emergence is often non-uniform and incomplete, reducing gains from this cash crop. This study investigated the effects of pineapple stem- derived protease (stem bromelain) based priming on pepper seed germination in relation to reserve mobilization (specifically, proteins and amino acids), germination, emergence and plant growth. These parameters were compared across two controls, (1) unsoaked seeds and (2) seeds soaked in deionized water, and seeds soaked in pineapple stem bromelain crude extract (treatment). Seeds were soaked in bromelain crude extract possessing a proteolytic activity of 6.25 tU or deionized water (first control) for 3 h at 35 C. Light microscopy revealed an abundance of protein bodies in the endosperm of the seeds prior to imbibition

Impacts of plastic debris on biota and implications for human health: A South African perspective

Entanglement and ingestion of plastics are the main ecological impacts of marine plastic debris on marine biota, but indirect effects such as the transport of alien species and benthic smothering are also important to note. Entanglement of invertebrates, sharks, turtles, birds and marine mammals is mainly caused by macroplastics (>5 mm), and leads to reduced mobility, ineffective foraging and subsequent mortality. The main plastic types associated with entanglement are improperly discarded fishing nets, lines, ropes and straps

A leadership model validation: Dimensions influential to innovation

Background: Current pressures for globalisation force organisations to explore, create and implement new ideas in order to remain competitive. This necessitates the need to utilise innovation to diversify products and services, introduce new technology, establish new managerial and administrative practices, and initiate transformation in other areas of the organisation. Objectives: This article explored the relationship between the latent variables, namely, rewards, resources, leadership vision and innovation, as postulated by De Jong and Den Hartog’s leadership model for stimulating innovation. Method: The research approach chosen to investigate the research questions was an ex post facto, cross-sectional field survey. Secondary data from a reputable financial institution with extensive business in three African countries (Botswana, Lesotho and Namibia) were used as the data were collected by the institution and made available to the researcher for further analysis. A complete sample size of N = 584 was obtained across the three countries. Confirmatory factor analysis was initially used to provide a confirmatory test of the measurement theory followed by structural equation modelling which allowed to test for regression amongst the latent variables (rewards, resources, leadership vision and innovation). Results: Structural equation modelling revealed that only leadership vision and resources were found to be statistically significant; rewards showed a negative relationship (r = −0.02) with innovation. Resources made the greater contribution (r = 0.75) to innovation, compared to leadership vision (r = 0.28). Conclusion: The study empirically validate and support the assertion of De Jong and Den Hartog (2007) that the latent variables resources and leadership vision positively correlate with innovation in the context of the financial services industry

Quantification and characterisation of microplastics ingested by selected juvenile fish species associated with mangroves in KwaZulu- Natal, South Africa

Though the number studies on microplastic ingestion by fish is growing, data on fish species charac- teristic of the South African coastline are scarce. This study quantified and characterised (physically and chemically) microplastics ingested by four species of juvenile fish (viz. Oreochromis mossambicus [Peters, 1852], Terapon jarbua [Forsskål, 1775], Ambassis dussumieri [Cuvier, 1828] and Mugil sp.), within four mangroves along the east coast of South Africa. Microplastics were isolated from whole fish using a proteinase K digestion method, and then quantified and characterised in terms of shape, chemical nature (plastic type), colour and length. Fibres (68%) and fragments (21%) were the dominant shapes found. Of the 174 fish sampled, 52% contained microplastic particles, with 0.79 ± 1.00 particles per fish. The average number of particles per fish did not differ significantly across species within sites and across sites but was higher than in juvenile fish of other species sampled in oceanic habitats. The main plastic types collected using 10 mm filters and identified with Fourier Transform Infrared Spectroscopy (FTIR), were rayon (70.4%), polyester (10.4%), nylon (5.2%) and polyvinylchloride (3.0%). Particle length ranged from 0.1 to 4.8 mm, averaging 0.89 ± 0.77 mm, but irrespective of length, particles were mostly blue in colour. This study provides evidence that juvenile fish inhabiting mangroves are consuming significant quan- tities of microplastics. Importantly, it should be noted that rayon, though the most abundant plastic type found, is a semi-synthetic fibre made from regenerated cellulose that is commonly reported in studies of this nature. The habitats studied serve as nurseries for numerous fish species; however, more detailed studies are needed to assess whether microplastic ingestion could compromise the health of these fish or whether these effects are dependent on species, feeding habit and/or plastic type

Oxidative Stress, Ageing and Methods of Seed Invigoration: An Overview and Perspectives

The maintenance of seed quality during the long-term conservation of plant genetic resources is crucial for averting the projected food crises that are linked to the changing climate and rising world population. However, ageing-induced loss of seed vigour and viability during storage remains an inevitable process that compromises productivity in several orthodox-seeded crop species. Seed ageing under prolonged storage, which can occur even under optimal conditions, induces several modifications capable of causing loss of intrinsic physiological quality traits, including germination capacity and vigour, and stand establishment. The problems posed by seed ageing have motivated the development of various techniques for mitigating their detrimental effects. These invigoration techniques generally fall within one of two categories: (1) priming or pre-hydrating seeds in a solution for improved post-harvest performance, or (2) post-storage reinvigoration which often involves soaking seeds recovered from storage in a solution. Seed priming methods are generally divided into classical (hydropriming, osmopriming, redox priming, biostimulant priming, etc.) and advanced (nanopriming, magnetopriming and priming using other physical agents) techniques. With the increasing popularity of seed invigoration techniques to achieve the much-desired enhanced productivity and resilience in the face of a changing climate, there is an urgent need to explore these techniques effectively (in addition to other important practices such as plant breeding, fertilizer application, and the control of pests and diseases). This review aims to provide an overview of ageing in orthodox seeds and invigoration techniques that can enhance desirable agronomic and physiological characters

Water security in South Africa: perceptions on public expectations and municipal obligations, governance and water re-use

South Africa is a water-scarce country with increasing pressure on its water resources. Urgent interventions are needed to protect water security within this rapidly developing country. This paper reports on an interdisciplinary Water Security Colloquium, convened by the South African Young Academy of Science in 2014. A selected group of water professionals from academia, civil society and local government was brought together to discuss water security under three focus themes: ‘public expectations and municipal obligations’, ‘water security and governance: challenges and advances’, and ‘water re-use: health and infrastructural considerations’. Participant perceptions were generated using a focus group methodology, combined with participatory data collection methods. Under each theme, inputs were categorised as ‘challenges’, ‘gaps in knowledge’, and ‘solutions/recommendations’ and these inputs were thereafter ranked in order of importance via a ‘voting’ process. Major challenges perceived included a lack of both skills and political will in government, a need to restore citizen trust in government intention and capability to deliver water-related services, and a failure to up-scale existing water re-use technology. Participants identified understanding of the process and implications of the Green and Blue Drop Programmes, knowledge transfer to the public, and the role of educators as major knowledge gaps. The top suggestions proposed included creating public awareness around and buy-in to initiatives to improve water security, accessible and user-friendly conversion of research results to implementation, and ensuring an active role for educators in creating awareness around water security. In view of the concerns identified, participants suggested as potential solutions: improving government and public understanding around water issues, incentivising water re-use and conservation, introducing rising block tariffs and improving human capacity development in the water sector. Developing the ecological infrastructure that protects both quantity and quality of water and building strong partnerships among all stakeholders were also recognised as key.Keywords: capacity development, education, governance, water security, water re-use, water conservation, local governmen