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Doctoral Degrees (Biological Sciences)

Permanent URI for this collectionhttps://hdl.handle.net/10413/12381

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Browsing Doctoral Degrees (Biological Sciences) by SDG "SDG2"

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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.
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    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.
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    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.