No description available.

More vegetable seeds are needed for developing countries to produce more vegetables. However, high temperature in these areas limits vegetable seed production. Leaf lettuce (Lactuca sativa L.) was grown in growth chambers at 21°C and exposed to different temperatures (28, 35, 38 and 42°C) for different exposure times (1, 4 and 7 hours) when flowers were at seven stages of development near anthesis.

No description available.

Call number: LD2668 .T4 1984 H46 / Master of Science

Graduation date: 1995

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

One of the factors that affect the post-harvest behavior of seeds is provenance. Different geographical locations are characterised by different environmental conditions, hence, plant materials harvested from different locations may respond differently to laboratoryinduced stresses. The aim of the present study was to assess the role that provenance plays on the degree of recalcitrance of a single species – a factor that needs to be taken into consideration when choices are to be made for plant germplasm conservation. In this study, seeds of Trichilia dregeana, which have been shown to display recalcitrant post-harvest behavior, were harvested from four locations that were slightly different in climatic conditions: Mtunzini (MTZN), Durban (DBN), Pietermaritzburg (PMB) and Port Edward (P.ED), all within the KwaZulu-Natal province of South Africa. Clean seeds, whose aril and seed coat have been removed, were subjected to different drying and chilling stresses and their responses to the stresses are examined. Excised embryonic axes of the seeds were also subjected to flash (very rapid) drying and their responses to the stress are shown. Although the vegetation of these locations can be categorized as being sub-tropical, the present study suggests that there may be ‘degrees’ in the sub-tropical nature based on the rainfall and maximum temperature data. The ‘degree of sub-tropicality’ is suggested to be in the order MTZN > DBN > P.ED > PMB. Mean seed size assessed as seed length, width and fresh mass varied significantly across the four regions, with seeds from MTZN being the smallest and those from P.ED being the largest. The shedding water content of the embryonic axes of the seeds for 150 min. However, shoot production, root and shoot length and dry mass accumulation showed that axes of seeds from MTZN were the most adversely affected by rapid drying while those from PMB were the least sensitive. When clean whole seeds were dried slowly by burying in silica gel for 36 h, all seeds of the four provenances still retained more than 50% of their shedding water. MTZN seeds lost viability completely from the 24 h of slow drying while seeds from the other three locations retained some viability after 36 h. The order of survival of slow drying was MTZN < DBN < P.ED = PMB. Storage of cleaned whole seeds at chilling temperatures (3oC, 6oC and 16oC) caused increase in the water content of the embryonic axes of the seeds across the four locations. All seeds of the four provenances had lost more than 50% survival after they had been stored at 3oC for 10 weeks. Survival was completely lost from the 12th week for MTZN seeds, from the 14th week for DBN and P.ED seeds and from the 16th week for PMB seeds. There was no survival recorded for seeds across the four regions at the 18th week. The seeds were able to tolerate storage at 6oC for a little longer than those stored at 3oC. Only MTZN seeds completely lost viability at the 18th week; seeds from the other three locations retained some viability throughout the 18 weeks of storage. Storage at 16oC was the most tolerable, as all seeds from the four provenances maintained some viability until the 18th week in storage, with MTZN having the least survival and those from P.ED having the highest survival. Phylogenetic analysis of the internal transcribed spacer (ITS) region of the DBN and PMB samples showed intraspecific levels of genetic variation, and were separated by a genetic distance of 0.9%, an indicator that differences in storage behavior, chilling and desiccation sensitivity between seeds obtained from different collection localities may be genetically based. This study showed that MTZN seeds were the most sensitive, while seeds from PMB and P.ED were the most tolerant, to drying and chilling treatments, respectively. The prevailing climatic conditions may have a bearing on the responses observed in this study. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.

Bibliography: leaves 155-182. Most agricultural crop seeds are 'orthodox' ie. desiccation is a necessary feature of their complete life cycle. Low moisture content lengthens the storage life of orthodox seeds. Recalcitrant seeds, which do not tolerate low moisture content, lose viability in dry storage. The thesis studies the role of sugars in desiccation tolerance in developing seeds and investigates other mechanisms which might be involved in desiccation tolerance and desiccation sensitivity.

Bibliography: leaves 155-182. / xiv, 182, [10] leaves, [11] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Most agricultural crop seeds are 'orthodox' ie. desiccation is a necessary feature of their complete life cycle. Low moisture content lengthens the storage life of orthodox seeds. Recalcitrant seeds, which do not tolerate low moisture content, lose viability in dry storage. The thesis studies the role of sugars in desiccation tolerance in developing seeds and investigates other mechanisms which might be involved in desiccation tolerance and desiccation sensitivity. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996?

Thesis (MTech (Agriculture))--Cape Technikon, 2001. / Onion seeds (cultivar Caledon Globe), and soil into which the seedlings were planted, were treated with various adjuvants including fungicides, a seed disinfectant and a soil sterilant, as well as soil-applied growth stimulants to determine the effect of these on germination of seed, the growth of plants and the storage life of onions obtained. Three sets of germination trials were undertaken in petri dishes, and sets of seed was also sown in deep seed trays. A trial planting was made and the crop graded and stored. Seed was also sown in pots in soil obtained from a commercial undertaking where poor germination had been obtained. A portion of this soil was pasteurised and a portion inoculated with Fusarium spp. Growth of these seedlings was then followed by re-sowing in the same pots using seed of additional cultivars.