Graduation date: 1995

No description available.

The seed storage fungi (xerotolerant) species of the genera Aspergillus and Penicillium} are renowned for their devastating effects on stored grain and grain products. In view of the fact that most of these fungi Iiberate toxins which can be harmful to both man and his livestock this problem is becoming increasingly relevant, particularly in developing countries. The seed storage fungi are said to be saprophytes and opportunistic invaders of dead or naturally dried organic matter, and as such no direct host-pathogen relationship has been ascribed to them. This dissertation reports aspects of an investigation into the modes/pathways utilised by these fungi in their infection of maize caryopses (seeds) and plants. The work involved studies on: the effects of protracted storage on maize seeds; the morphology of storage fungi; extra-cellular enzymes of storage fungi; the pathways utiIised by the storage fungi in invasion of seed tissues; and the effects of the storage fungi on the seeds. Correlations have been made on a species basis between the extent of seed deterioration and fungal aggressiveness. The results of these investigations indicated that apart from affecting seed vigour and viability, these fungi can also affect plant vigour. This latter aspect was further investigated to determine whether a seed storage fungus could infect germinating maize seeds, and remain an internal contaminant of the tissues during plant growth and development. These latter studies revealed that Aspergillus flavus var. columnaris is capable of systemic transmission from one seed generation to the next. This hitherto unrecognised phenomenon apart from indicating that the fungal species is in fact a biotroph as well as a saprophyte, also has implications In control measures. / Thesis (Ph.D.)-University of Natal, Durban, 1990.

Seeds of wild rice (Zizania palustris var. interior) have been reported to show highest survival when dehydrated at 25 QC. It has also been reported that axis cells sustained least damage at this drying temperature. In the present study, a linear relationship between drying rate and dehydration temperature was established. Whereas highest positive tetrazolium staining and lowest leakage were recorded for seeds that were dehydrated at 25 QC, maximum germination was recorded for seeds dried at 20 QC. A proportion of seeds showed the presence of glasses, irrespective of the dehydration temperatures used. Parameters of the glass to liquid transition, however, correlated with neither water content nor sugar profiles. The ratio of raffinose to sucrose was similar among all the treatments. A hydroperoxide test revealed a linear relationship between peroxide levels and temperature of drying although the levels of fatty acids were not correlated with hydroperoxide levels. Butanal levels and total aldehydes evolved, on the other hand, showed a high negative correlation with peroxide levels. Electron microscopy showed that the variability and relative abundance of peripheral membrane complexes (PMCs) was the highest for cells of embryonic axes dehydrated at 25 QC and the lowest for embryonic axes of seeds dried at 10 QC. Furthermore, intramembrane particles (IMPs) were evenly distributed in cells of axes dried at 25 or 37 QC. In contrast, membranes of cells of axes dehydrated at 10 QC showed large IMP-free areas. The relative abundance of IMPs was the highest for cells of embryonic axes dried at 25 QC, and the lowest for cells of axes dehydrated at 10 QC. From these observations, it is suggested that membrane phase transition, with the concomitant elimination of proteins, accompanies dehydration of Z. paluslris seeds at 10 QC, whereas at 37 QC peroxidation may predominate. / Thesis (M.Sc.)-University of Natal, Durban, 1996.

The International Seed Testing Association and the Association of Official Seed analysts define seed vigour as the ability of a seed lot to perform during the germination process and crop stand establishment under a wide range of environmental conditions. There are many ways to determine seed vigour, but few satisfy the requirements of being simple, inexpensive and reproducible, among others, to permit the seed industry to adopt seed vigour as an indicator of seed quality when they sell seeds. Hence, the standard germination test, which is performed under uniform and favourable conditions, is generally used to indicate seed quality when seeds are marketed. The objective of this study was to determine the performance of tomato and pepper seeds in response to pre-germination hydration and dehydration relative humidities (12%, 49% and 75% RH). Before hydration, seeds were hydrated at three temperatures (10°C, 20°C and 30°C). Hydration was performed by imbibing pre-weighed pepper ('Santarini' and 'California Wonder'), Chilli and tomato ('Heinz', 'Marondera' and 'Roma') seeds for 2 h in 10 ml of distilled H(2)0 per 100 seeds at 10°C, 20°C and 30°C. Dehydration was performed by change in seed mass determined during a 72-hour dehydration at 12%, 49% and 75% RH. Seed performance in response to imbibition and dehydration was determined by leakage of electrolytes from seeds during imbibition, laboratory germination capacity and seedling emergence under simulated shadehouse nursery conditions. A pot experiment was conducted to determine the effects of seed treatments on yield. Seed mass increased by about 50% during the 2-hour of hydration. Dehydration was hastened by decreasing the RH, and 12% RH significantly (P < 0.05) reduced the post-imbibition seed moisture content compared with 49% and 75% RH. The latter two relative humidities reduced the seed moisture content to about 10% and 15%, respectively, for all cultivars, irrespective of imbibition temperature. Low imbibition temperature (10°C) significantly (P < 0.01) increased electrolyte leakage, compared with high imbibition temperatures (20°C and 30°C), which were not significantly different from each other. At all hydration temperatures, low RH (12%) caused a significant (P < 0.01) decrease in seed germination whereas 49% RH and 75% RH apparently had a priming effect on seeds. There was no significant difference between imbibition temperatures, with respect to seed germination, but 100G caused a significant decrease in germination index, a measure of seed vigour. Seedling emergence was significantly (P < 0.01) reduced by both low imbibition temperature (10oG) and low dehydration relative humidity (12% RH). The negative effects of low imbibition temperature and rapid dehydration at 12% RH were also observed as stunted seedling growth. Principal component analysis and linear regression were used to determine a statistical model to predict seedling emergence from germination percentage. The model predicted emergence consistently, but it overestimated it by about 2% to 3%. It is concluded that low imbibition temperature and rapid dehydration can be used to simulate stress to determine seed performance in pepper and tomato. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

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. / Thesis (M.Sc)-University of KwaZulu-Natal, 2007.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xx, 305 p.; also includes graphics. Includes bibliographical references (p. 278-305). Available online via OhioLINK's ETD Center

Endosperm mobilization studies in cereal seeds are typically based on the view that α-amylase synthesis in the aleurone tissue is controlled by gibberellins from the germinating embryo. However, α-amylase is often produced by de-embryonated endosperm segments in the absence of added gibberellins. Two specific systems exhibiting this phenomenon were examined; 1) the ability of amino acids to promote α-amylase production in de-embryonated wild oat segments and, 2) autonomous starch hydrolysis (in the absense of exogenous GA₃ or amino acids) in de-embryonated barley endosperm halves. Specific technical problems were addressed prior to the onset of these studies. Captan (66 μM) controlled fungal contamination in the incubation medium without inhibiting GA₃-induced sugar release, which occurs following seed sterilization in hypochlorite and ethanol. The Nelson-Somogyi reducing sugar assay was not suitable for quantifying sugar levels in incubation solutions containing amino acids as cysteine, cystine, serine, tryptophan and tyrosine interfered with the assay. Absorbance (540 nm) increased as concentrations increased from 0.1 to 1 mM; simultaneous additions of amino acids with glucose resulted in absorbance values higher than glucose alone. MnCl₂ (0.5 mM) inhibited absorbance in the presence of glucose and the amino acids serine, cystine, and tryptophan. The ability of individual amino acids to promote α-amylase production in wild oat endosperm halves is yet unclear. Although certain amino acids were shown to enhance enzyme production, the level was often quite different between replicated experiments. However, incubation of endosperm halves in a mixture of 18 amino acids consistently promoted α-amylase synthesis; enzyme production was further enhanced if a level of GA₃ (10⁻⁹ M), which was too low to promote α-amylase synthesis alone, was included within the amino acid mixture. Autonomous endosperm mobilization (AEM) was variable in different barley cultivars. High sugar release correlated well with α-amylase production; the levels were similar among individual cultivars harvested in two different seasons. The onset of AEM was delayed, as the majority of sugar was released in the second day of incubation. AEM was greatly reduced by inhibitors of RNA (6-methyl purine) and protein (cycloheximide) synthesis suggesting that AEM was a result of the de novo synthesis of α-amylase. Incubation conditions greatly affected AEM. Although AEM was high at acidic pH (4.6-5.6), it was greatly reduced at basic pH (7.6-8.6). AEM increased as the temperature was raised to 28°C. Low levels of Ca²⁺ (0.25-0.5 mM) enhanced AEM whereas higher amounts (0.5-1 mM) were inhibitory. Incubation of wild oat endosperm halves in solutions of pre-emergence herbicides affected GA₃-induced sugar release to varying extents when applied at field application levels. Only triallate (22% reduction) and trifluralin (21% reduction) prevented sugar release (only - 5 at 3x10⁻⁵ M); no inhibition was seen following incubation in EPTC (5xl0⁻⁵, 5xl0⁻⁶ M), metribuzin (5xl0⁻⁶, 1x10⁻⁶M) and oryzalin (3xl0⁻⁵, 3x10⁻⁶M). However, the higher concentrations of each herbicide effectively inhibited the development of wild oat seedlings. / Land and Food Systems, Faculty of / Graduate

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Call number: LD2668 .T4 1949 M21 / Master of Science