Browsing by Author "Erdey, Deon Philip."

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The potential of hot water treatments for curtailing seed-associated mycoflora.
(1995) Erdey, Deon Philip.; Berjak, Patricia.; Mycock, D. S.
The consequences of toxigenic fungi associated with stored seed have stimulated these investigations aimed at developing treatments to minimise this mycoflora, without significantly reducing seed quality or viability. The effects of immersion in water at 55, 57 and 60 QC for durations of 5 to 60 min were assessed for maize (Zea mays L.) seed in terms of fungal status, water uptake, electrolyte leakage, germination and seedling establishment. These assessments were conducted immediately after treatment, after re-dehydration for 2 days in an ambient air stream, and following a 1 month storage period under either cold (4 QC) or ambient (25 QC) conditions (33% and 91% RH, respectively). In all cases, the results are compared with those of control seeds and seeds pre-imbibed for 4 h at ambient temperature. The level of internal contamination, represented almost entirely by Fusarium moniliforme Sheldon, declined significantly when assessed immediately after treatment, the efficacy of which increased with increasing temperature and duration of treatment. Seeds immersed in water at 55 QC for a duration of 15 min exhibited an 85% reduction in infection levels, when compared with those of the control, while those treated at 57 and 60 QC (same duration) were uninfected. Immersing seeds in hot water, however, resulted in a lag in germination rate and drop in germination totality, the degree of which was enhanced by increasing duration and temperature of treatment, suggesting the status of the manipulation to be an accelerated ageing treatment. The electrolyte leakage studies indicated that the reduced germination performance of these seeds was not due to plasmalemma disorganisation. These deleterious effects, however, were counter-balanced as seeds treated at 55, 57 and 60 QC for durations up to 60, 30 and 10 min, respectively, produced plants of superior quality than those of the control, which is ascribed to the reduction of systemically transmitted pathogens. The efficacy of the hot water treatment in reducing the levels of seed infection and improving seedling quality was enhanced by subsequent re-dehydration. The reduction in seed-associated mycoflora was maintained following storage for 1 month at both 4 QC (33% RH) and 25 QC (91% RH). However, both seed and seedling quality were adversely affected following storage even under cold, dry conditions, which may be a consequence of the pre-treatment history of the seeds, which had been cold-stored for two years prior to the experiments. Applied as a pre-sowing treatment, therefore, hot water treatment shows promise for producing a crop of superior quality, less prone to fusarial pathogenesis. This treatment may be of particular importance to Third-World subsistence communities.
Sub-imbibed storage of recalcitrant seeds of four species.
(2007) Eggers, Sharon Kim.; Berjak, Patricia.; Pammenter, Norman William.; Erdey, Deon Philip.
The seeds of Trichilia dregeana, Trichilia emetica, Podocarpus henkelii and Syzygium cuminii display the characteristics typical of recalcitrant seeds. It is the phenomena of ongoing metabolic activity and desiccation sensitivity that render them unsuitable for storage by the conventional methods used for orthodox seeds. Investigations on the storage responses of 'sub-imbibed' (partially dried) and fully hydrated seeds of all four species were carried out to study the effects of partial drying on viability and subsequent storage lifespan; i.e. to assess whether 'sub-imbibed' storage is feasible for these species. The outcome of this investigation was proposed to contribute to the resolution of the argument that storing recalcitrant seeds at lowered water contents might extend their longevity; i.e. storage at a relatively high water content but below the fully hydrated level, might prevent germination but would not be sufficient to be injurious to the seed. Seeds of T. dregeana, T. emetica, P. henkelii and S. cuminii were dried to various target moisture contents (which were determined for each species in the initial drying experiment) and then subjected to storage for 3-22 weeks at 6, 16 and 25°C (in sealed containers). In parallel, seeds of each species were stored at the shedding water content. The seeds were periodically removed for sampling, and assessed for water content, germination, respiration, electrolyte leakage and microscopical features. Storage temperature appeared to affect viability of seeds of T. emetica and T. dregeana which displayed characteristics of chilling sensitivity. Storage at 6°C was detrimental (when compared with seeds stored under the same conditions at 16 and 25°C), but regardless of whether the seeds were undried or partially dried prior to storage. The seeds of P. henkelii did not demonstrate chilling sensitivity, the viability not being compromised at 6°C compared with those seeds stored at 16 and 25°C. Syzygium cuminii seeds were not subject to storage at 6°C because previous work indicated that they would be chilling-sensitive. Storage of 'sub-imbibed' seeds of T. dregeana, T. emetica, P. henkelii and Syzygium cuminii does not to confer any benefit over seeds stored in the fully hydrated state; rather it appears to be deleterious to seed survival during storage. This was apparent from the assessment of viability, electrolyte leakage and respiration. Vigour and viability of the 'sub-imbibed' seeds of all species declined more rapidly than the fully hydrated seeds. The only exception was P. henkelii seeds stored at 25°C, the fully hydrated seeds showed no survival after 11 weeks in storage, while 88% of the 'sub-imbibed' seeds survived this period. These results were, however, attributed to the proliferation of fungi on the fully hydrated seeds at 25°C. Although ultrastructural observations were made only on the T. emetica seeds, it was apparent that the cells from the 'sub-imbibed' seeds (after storage at 16 and 25°C) showed extensive degradation, with the intra-cellular components being largely unrecognisable. The cells from the seeds stored in the fully hydrated condition at 16 and 25°C maintained integrity and appeared metabolically active. In keeping with the suggestion that T. emetica seeds are chilling sensitive, the ultrastructure of the cells from both the 'sub-imbibed' and fully hydrated seeds showed deteriorative changes. All the results of the present study indicated that storage in the 'sub-imbibed' state is deleterious to seed survival. It is apparent that the removal of water, however small a proportion, accelerates seed deterioration during storage. Thus 'sub-imbibed' storage has no practical application for the storage of recalcitrant seeds.