The wild watermelon, Citrullus lanatus L. was among the most important foodstuffs to a number of African communities, until the colonists introduced their own foodstuffs in a process that was highly supported by the laws of the time. However, there is now a growing realization by government and other stakeholders of the importance of indigenous crops (including the wild watermelon) as substitute food stuff to improve food security. Wild watermelon is an adaptable crop, which can contribute to food security as it has a potential for commercialization. However, there are no records on the production of wild watermelon with reference to optimum planting density and the effects of mulch on the growth and development of the crop. To investigate this issue, which the smallholder farmers are faced with, a study that designed to (a) determine the effects of population density on growth and yield of wild watermelon and (b) investigate the effects of mulching on growth and yield of wild watermelon under field conditions. The study was undertaken over two seasons during which two different types of propagules, namely seed and seedlings, were used. A field study of wild watermelon establishment and yield using seeds and seedlings to compare the effects of different population densities (3000, 6000, 9000 and 12000 plants/ha) and mulching rates (0, 2.5 and 5 t/ha) based on the availability of grass on soil water, temperature, vine length (height), number of branches and leaves per plant, fruit number, total yields, fruit size and weed distribution was conducted at Dohne Agricultural Development Institute (Lat-32.52521; Long – 27.46119, alt. 907 m above sea-level) over a two year period ( 2009 – 2011 growing season). Results on data collection and analysis of growth and yield parameters are that: When seed was used as means of propagation, there were significant effects (p 0.05) of mulching and population density, on soil temperature and volumetric water content. However, no significant differences were found with regards to vine length, number of branches and leaves per plant. Concerning yield, there were no significant differences recorded on any of the measured parameters in response to mulch. Yet, with population density, significant differences were noted on fruit number per hectare and total yield at p 0.05. The number of fruits and total yield per hectare increased as plant population increased, resulting in high yields to range from 9000 -12 000 plants per hectare with both seed and seedling propagules used during the study period with or without mulching. Seedling propagules were associated with differences in soil temperature and volumetric water content with regards to mulching and population density (p 0.05). Results obtained from this study in both years, revealed that yield is more influenced by plant population density than by mulching. Mulching has been found to be ineffective as far as growth and yield are concerned, but it was found to influence soil temperature and volumetric water content. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Cowpea (Vigna unguiculata (L.) Walp) is an important protein-rich grain legume of major economic importance. It is widely grown by small-scale farmers in the arid and semi-arid regions of the world where it is cultivated for its leaves, fresh immature pods and dry grains. However, it is also an underutilized grain legume. In sub-Saharan Africa where most of the cowpea is produced, drought stress is one of the major factors limiting its productivity. Despite the inherent capacity to survive drought stress, several cowpea varieties are affected by mid and late season drought. Therefore, varieties with a higher tolerance to drought stress are required to obtain higher and more stable yields. The objectives of this study were: (i) to determine morphological responses of four dual-purpose cowpea landraces to water deficits during vegetative and reproductive stages (ii) to determine physiological responses of four dual-purpose cowpea landraces to water deficits and recovery during the reproductive stage (iii) to determine yield performance of cowpea landraces after recovery from water stress and how this relates to (ii) above. Four cowpea landraces namely; Lebudu, Lehlodi, Sejwaleng and Morathathane collectedfrom Kgohloane and Ga-Mphela villages, Limpopo Province, South Africa were used in the study. Pot experiments were conducted under glasshouse conditions at the Controlled Environment Facility (CEF), University of KwaZulu-Natal. The first pot experiment evaluated the morphological responses of four cowpea landraces to water stress and recovery. The study was conducted as a single factor experiment laid out in randomized complete block design (RCBD). The treatments (four cowpea landraces) were each planted in 40 pots giving a total of 160 experimental units (drained polyethylene pots with a 5 litre capacity). Each plant in each pot was treated as a replicate. Plants were well-watered until the formation of six fully expanded trifoliates, then irrigation was withheld for 28 days to simulate drought stress during the vegetative growth. The imposition of drought stress was terminated by re-watering all plants after 28 days. The cowpea plants were re-watered sufficiently and allowed to grow until the four landraces reached 50% flowering stage. Watering was withheld again at 50% flowering for a two-week period for all the four landraces to simulate drought stress during the reproductive growth. The second experiment was conducted to investigate physiological responses of the four cowpea landraces to water stress during the reproductive stage. The experiment was laid out as a 4 x 2 factorial treatment structure in randomized complete design (CRD) with the following three factors: cowpea landraces – 4 levels (Lebudu, Lehlodi, Sejwaleng and Morathathane), water regimes – 2 levels (stressed and well-watered) treatment combinations each replicated 20 times (20 pots each containing one plant) giving a total of 160 experimental units (drained polyethylene pots with a 5 litre capacity). Data on morphological responses were collected and included: number of green vs. senesced leaves, visual assessment of leaf greenness, stem, branch greenness and survival percentage. Physiological responses to water stress were determined during the reproductive stage and included: leaf water potential, relative water content, stomatal conductance, proline content, chlorophyll content, carotenoid content, chlorophyll a content, phenolics (free and membrane-bound), total antioxidant capacity and chlorophyll fluorescence parameters (Fv/Fm). Genstat 14th edition (VSN International, UK) was used to perform analyses of variance (ANOVA) and differences between means were determined by the Least Significant Differences (LSD) at the 5% probability level. Landraces showed different morphological responses during both vegetative and reproductive growth stages. Lebudu, Lehlodi and Sejwaleng displayed a strong ability to maintain stem greenness longer as compared to Morathathane during vegetative growth. Lebudu delayed leaf senescence more than other landraces; no differences in survival were observed. All landraces survived for 28 days without water and resumed growth after re-watering. During the reproductive stage, Lebudu displayed a strong ability to maintain leaf, branches and stem greenness longer and showed relatively higher tolerance to drought stress compared to other three landraces. Water stress caused a decline in leaf water potential, relative water content, carotenoid content, chlorophyll content, stomatal conductance and increased proline content, phenolics, chlorophyll a content, total antioxidant capacity and while chlorophyll fluorescence parameter, Fv/Fm, was not affected. All landraces maintained higher relative water content above a critical threshold with Sejwaleng maintaining a significantly higher RWC (69%) than Lehlodi, Lebudu and Morathathane. Morathathane developed a more negative leaf water potential at maximum stress than Lebudu, Lehlodi and Sejwaleng. Stomatal closure was observed in all cowpea landraces during water stress, but re-opened after re-watering. Chlorophyll content was considerably reduced in Morathathane as compared to Lebudu, Lehlodi and Sejwaleng. No significant differences were observed between the cowpea landraces with respect to carotenoid content at maximum stress. Chlorophyll a content increased significantly for Morathathane as compared to Lebudu, Lehlodi and Sejwaleng. High accumulation of proline was observed for Lebudu, Lehlodi and Morathathane as compared to Sejwaleng, which showed a very slow accumulation of proline. Lebudu, Lehlodi and Sejwaleng showed an increase in phenolic compounds while a decline was observed for Morathathane. Total antioxidant capacity (TAOC) was high in all cowpea landraces during water stress. Also, all chlorophyll fluorescence parameters showed that cowpea landraces had efficient photo-protection mechanisms during drought stress. After re-watering, relative water content, leaf water potential, stomatal conductance, chlorophyll content, carotenoids, chlorophyll a, proline content and TAOC recovered and reached the same level as that of well-watered plants. All four landraces were re-watered after the imposition of stress and above ground biomass, pod mass and number and seed yield determined. Although there was a reduction in the total above-ground biomass, pod mass and number in all four landraces under water stress compared to the well–watered treatment; this was not statistically significant (P > 0.05). Furthermore, no significant differences (P > 0.05) were observed between the four landraces with respect to seed yield under stressed and well-watered conditions. This study established that cowpea landraces vary with respect to the various morphological and physiological adaptive mechanisms in response to water deficits. Such adaptive mechanisms probably ensure their survival under severe water stress conditions until the next rainfall and therefore allowing them to produce reasonably relatively higher leaf and seed yield. Detailed knowledge of these mechanisms in the landraces could be useful in the genetic enhancement and breeding for drought tolerance in the existing cowpea germplasm. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

An experiment was conducted at Pongola (27°24´S, 31°25´E; 308m altitude) in South Africa to study the effects of season on growth and potential biomass and sucrose yields on nine commercial sugarcane cultivars. The treatments that were the focus in this study consisted of the cultivars NCo376, N25 and N26 ratooned in March, April, May, August and December. The crops were well fertilized and kept free of weeds and diseases. Irrigation applications were scheduled with a computer programme to keep the crops free of stress at all times. Shoot populations were counted regularly to study shoot density dynamics. Leaf appearance rates, sizes, numbers and senescence were measured to study the development of green leaf area. Green foliage, dead trash and stalk mass were measured at 4, 8, 10, 11 and 12 months in each of the starting times and also at 13 months in the March, April and May ratoon crops. The fibre, sucrose and non-sucrose content of stalks were determined on these harvesting occasions. Yields were calculated in terms of individual shoots and area (m‾²). The fraction of PAR intercepted by the developing canopies was measured until full canopy and daily intercepted solar radiation was interpolated for the entire crop. An automated meteorological station adjacent to the experiment site provided daily weather data. Shoot densities were described by thermal time, however, average peak shoot densities were lowest in the May ratoon (31.8 m‾²) and highest in the December ratoon (48.7 m‾²). Shoot senescence was most rapid in August and December ratoons. At the final harvest shoot densities were highest in the March, April and May ratoon (14.8 to 14.2 m‾²) crops. NCo376 (16.4 m‾²) and N25 (13.6 m‾²) had higher final shoot densities than N26 (10.5 m‾²). Leaf appearance rate was also well described by thermal time, however the first twelve leaves took longer to appear in crops started in December i.e. the first phyllochron was longer (109.5°C d) than in crops started at other times (80.4 to 94.5°C d). Leaves produced during the early stages of December and August ratoon crops were larger (e.g leaf number 13 of N26 was 443 to 378 cm²) than in other crops. April and May ratoon crops produced much smaller leaves (e.g leaf number 9 of N26 was 170 to 105 cm²). Leaf senescence was slower in April and May ratoon crops (0.36 to 0.46 leaves per 100°C d) than in March (0.51 to 0.59 leaves per 100°C d) or August and December ratoon crops (0.60 to 0.68 leaves per 100°C d). December ratoon crops produced very high green leaf area indexes (LAI) (>7.0) at the age of four months; all other crops had lower LAI (3.3 to 6.0) and most peaked later (8 to 11 months of age). The LAI of N25 peaked at the age of 8 months while NCo376 and N26 peaked when 10 to 11 months old. Seasonal fraction of solar radiation intercepted was high in the March ratoon crops (0.84) and declined to 0.63 in the May ratoon crops and was highest in the December ratoon crop (0.88). N26 intercepted lower fractions of PAR than NCo376 and N25, particularly in the May and August ratoon crops. Biomass accumulation, although initially slow, tended to be linear in the March, April and May ratoon crops in relation to intercepted radiation. In August and particularly in the December ratoons biomass accumulation was initially rapid, and RUEs were high (2.65 g MJ‾¹ at 114 days in the December ratoon crops). However, biomass accumulation slowed when these December ratoon crops experienced winter. Low growth rates after winter, as well as low shoot densities resulted in December ratoon crops having produced significantly lower above-ground biomass yields (4 886 g m‾² at the age of 12 months) than March, April and May ratoon crops (6 760 to 5 715 gm‾² at the age of 12 months). The December ratoon crops responded poorly to the better growing conditions in spring and second summer and accumulated little biomass after winter. N26 shoots grew rapidly during the first 6-8 months of the December ratoon crop and it yielded better than NCo376 and N25 at harvesting (biomass yields were 5.8 and 13.3% higher at the age of 12 months, respectively). April ratoons produced significantly higher biomass yields (6 760 g m‾²) than March, August and December ratoons. May ratoon crops produced the highest cane fresh mass yields (18 151 g m‾²) and April, May and August ratoons produced significantly higher sucrose yields than March and December ratoons. The highest sucrose yield was produced by the April ratoon crop of N26 (2 385 g m‾²). On average, across the five ratoon dates, NCo376, N25 and N26 produced similar sucrose yields (1 902 to 1 959 g m‾²). Foliage production was severely limited during winter while sucrose accumulation was less affected by the low temperatures, resulting in accumulation of sucrose in the top sections of the culm. Low temperatures slowed the development of canopies in March, April and May ratoon crops, but these crops were able to recover their growth rates and produced high biomass and sucrose yields at the age of 12 months. The December ratoons experienced low winter temperatures (<12°C) when they had already accumulated relatively high yields and became moribund during winter. They were unable to accumulate any significant amounts of biomass during final four months before the final harvest at the age of 12 months. NCo376, N25 and N26 all yielded poorly in the December ratoon crop. However, there are cultivars that appear to be less sensitive to the low winters and are able to yield relatively well when they are ratooned in December. Sucrose yields of March, April and May ratoons were increased substantially (10.6 to 22.7%) by harvesting at the age of 13 months rather than at the age of 12 months. The poor growth of December ratoon crops after winter is possibly due to the recently revealed feedback signaling by high sugar levels induced by low temperatures on photosynthesis. The incorporation of the effects of low temperature and the feedback signaling with the objective of better simulating yields of December ratoons is a proposed study at the South African Sugarcane Research Institute. Annual mean sucrose yields of NCo376, N25 and N26 crops were estimated to be 17% higher in March than in December ratoons. The suggested short term remedy therefore of the poor December yields is to shift milling seasons to include March and exclude December harvested crops in the northern irrigated regions. March crops grow vigorously during the months close to harvesting and therefore have lower levels of sucrose content which can be corrected with chemical ripeners. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Despite the importance of taro (Colocasia esculenta L. Schott) as a food security crop, scientific research on it is scanty in South Africa. Production site, planting date and fertiliser regime affect crop performance and quality, particularly that of cultivars, because they tend to be adapted to specific localities. Storage temperature and packaging method on the other hand affect the shelf-life. To investigate performance and quality of three taro cultivars in response to planting date and fertilisation, a study was carried out at two sites in KwaZulu-Natal, South Africa (Ukulinga and Umbumbulu), during the 2007/2008 growing seasons. The effect of two storage temperatures (12oC and ambient temperature) and three packaging methods (polyethylene bags, mesh bags and open boxes) on cormel quality following storage was also investigated for three cultivars. Delayed planting negatively affected the number of cormels plant-1 and fresh cormel mass plant-1. Fertilisation and cultivar affected the number of cormels plant-1 and fresh cormel mass plant-1 only when planting was done in October and November at both sites. Fertilisation increased the number of cormels plant-1 for all cultivars except Dumbe-dumbe. Dumbe-dumbe had the lowest number of cormels plant-1 but the highest number of marketable cormels plant-1. Dumbe-dumbe showed the lowest fresh cormel mass plant-1 in October and the highest in November at Ukulinga. Fertisation increased fresh cormel mass plant-1 in October at Umbumbulu. Dry matter content was negatively affected by fertilisation at Ukulinga. The response of dry matter content, specific gravity, protein, minerals, reducing sugars and starch content was variable depending on cultivar. Delayed planting negatively affected starch content for Dumbe-dumbe and Pitshi at Ukulinga. Fertilisation decreased starch content of Pitshi, while delayed planting increased sugar content for Dumbe-dumbe and decreased it for Mgingqeni and Pitshi at Umbumbulu. Dumbe-dumbe had higher starch content and higher reducing sugars. Considering all growth and quality parameters, it is recommended that Dumbe-dumbe is the best taro cultivar for crisping and the best time to plant it is October with 160 kg N ha-1 of organic fertiliser and November with 320 kg N ha-1 at Ukulinga whereas at Umbumbulu the best time to plant Dumbe-dumbe is October with 320 kg N ha-1 of the fertiliser. Starch granules degradation, alpha-amylase activity and sprouting increased with storage time and storage temperature. Cormels of Mgingqeni stored in polyethylene bags showed highest alpha-amylase activity and sprouting. Reducing sugar content increased and starch content decreased with time in storage and decline in storage temperature. It is recommended that taro cormels be stored in mesh bags at 12oC. The chapters of this thesis represent different studies presented as different papers. Chapter 1 is a general introduction to explain the study background and hypothesis. Chapter 2 is a general review of literature. Chapter 3 is on growth, development and yield of taro in response to planting date and fertilisation. Chapter 4 is on the influence of planting date and organic fertiliser on crisping quality of taro cormels. Chapter 5 is on changes in the surface morphology of starch granules and alpha-amylase activity of taro during storage. Chapter 6 is on the effects of pre- and post-harvest practices on starch and reducing sugars of taro. The last chapter is a general discussion and conclusions. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Cowpea (Vigna unguiculata. L) is an important African crop. However, it is also an underutilized grain legume. Consequently, there is not enough research data on cowpea seed physiology. Whereas there is evidence of cowpea being a drought tolerant crop, there is no evidence to associate plant drought tolerance with seed quality in response to water stress. This study sought to understand the effect of production site and water stress on cowpea seed quality development with respect to germination capacity and vigour. Patterns of raffinose family of oligosaccharides (RFO) during seed development to mature dry stage were used to physiologically relate seed performance to water stress. The effect of water stress and exogenous ABA on the accumulation of stress LEA proteins (dehydrins) in relation to seed quality development and germination was investigated. RFOs are known for their roles in desiccation sensitivity but no studies have shown their significance in cowpeas. Seeds of six cowpea cultivars were produced at two distinct growth sites characterised by irrigated and dry land conditions. The seeds were assessed during six developmental stages, for water content, dry matter accumulation, and performance. Harvested seeds were then planted in a pot experiment under controlled conditions to examine the effect of water stress on seed quality development and data collected during three developmental stages. Harvested seeds from the pot experiment were subsequently analyzed for changes in RFO accumulation during development using gas chromatography. The seeds were also used to investigate the effect of water stress and ABA on the accumulation of stress LEA proteins (dehydrins) in relation to seed quality development in cowpea. In addition, this study evaluated the use of image analysis as a method that can be used to objectively determine seed coat colour variation in cowpea. Statistical variation in individual seed’s solute leakage for cowpea cultivars differing in seed coat colour and produced under different environmental conditions was explored and correlations were done between seed conductivity test with other aspects of seed performance during germination. Furthermore the results of the conductivity test were compared with accelerated aging test, in relation to seed performance. The study provided evidence that cowpea seed lots produced under different environmental, and possibly management conditions may not differ with respect to seed quality as determined by germination capacity and vigour. However, significant differences between sites with respect to seed maturation patterns determined by water content and dry matter accumulation were observed. Adverse maternal environmental effects on the subsequent performance of seeds in a drought tolerant crop may not necessarily lead to poor performance. Cultivar differences in response to simulated drought conditions at the whole plant and tissue level can be considerable and highly variable; however, these differences may not have adverse effects on the germination and vigour of the seeds. Drought avoidance mechanisms at the whole plant level in cowpea are quite efficient in allowing the species to adapt to simulated drought conditions. These mechanisms may allow the cowpea cultivars to maintain metabolism and restore conditions for their continued growth under water stress; and produce few seeds of high germination capacity and vigour. Stachyose was found to be the predominant member of the raffinose family of oligosaccharides in cowpea. It is suggested that stachyose accumulation could be used as an indicator of stress tolerance in cowpea. However, the relationship between RFO concentration and the acquisition of desiccation remained as a matter of speculation in the present study and is still generally inconclusive. There was no evidence to suggest the acquisition of maximum desiccation tolerance is associated with maximum seed vigour. It is suggested in cowpea, which is drought tolerant, that maximum vigour does not necessarily imply the acquisition of maximum desiccation tolerance; rather there is a minimum level of desiccation tolerance that is required for the development of optimal seed vigour. The use of an in vivo approach in the study of LEA function in cowpea enabled the accurate comparison of two different groups of LEA proteins in developing cowpea seeds under conditions of water stress and in relation to germination and vigour. Both group 1 LEA and group 2 LEA (dehydrin) were shown to increase in concentration in response to water stress. In addition group 1 LEA protein was observed to be relatively abundant in cowpea seeds. A maternal influence on LEA protein gene expression under conditions of water stress, which may induce dehydrin accumulation vii during the earlier stages of seed development, was implied by the observation that dehydrin-like proteins were induced after two weeks of development in cowpea plants subjected to stress during the vegetative phase. In addition, the exogenous application of ABA delayed radicle protrusion; this was associated with a delay in the disappearance of LEA proteins and is suggestive of a relationship between LEA protein accumulation and the acquisition of desiccation tolerance. The study has demonstrated that image analysis can objectively discriminate seed coat colour variation in cowpea. Dark coloured seeds in general performed better than light coloured seeds; however seed coat colour was not always associated with better performance. A newly developed Aging Stress Differential Index (ASDI) has been used in this study to demonstrate a link between seed coat colour and sensitivity to water stress. The ASDI correlated well with the observations relating stress tolerance to stachyose accumulation. The skewed distribution patterns in individual electrical conductivity and the presence of extreme values may have implications with respect to the suitability of using standard statistical analyses which compare mean values to evaluate such data. In addition variation in individual electrical conductivity may also be influenced by cultivar differences and the chemical composition of the seed coat. Therefore associations between seed coat colour and electrical conductivity as a measure of performance should be treated with caution. The AA test does reflect changes in seed vigour, however ranked electrical conductivity values after AA did not consistently reflect differences in seed performance between cultivars and sites, and they did not correlate well with other aspects of performance. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

The aim of the study was to determine the effect of day/night temperatures (22/l6°C, 2712l oC and 33/27°C) and phosphorus levels (0, 0.12 and 1.2g per 20 kg soil) on seedling establishment and seed viability during three stages of seed development (15, 22 and 33 days after flowering) for seed of normal and quality protein maize cultivars. Soluble carbohydrate accumulation and mineral element content were determined using environmental scanning electron microscopy (ESEM) in relation to seed phytate levels and seed germination capacity at different stages of development. Leaf emergence rate and plant height during seed development were significantly (P < 0.05) influenced by temperature and phosphorus nutrition. Phosphorus in seed is stored primarily in the form of phytic acid, also known as phytate. Accumulation of phytate takes place during maturation phase of seed development. Phosphorus nutrition and temperature also caused a.significant (P < 0.05) increase in seed germination at all stages of seed development. Furthermore, phosphorus nutrition and temperature influenced occurrence of soluble carbohydrates in seeds. Myo-inositol, the sugar alcohol that forms the basic structure of phytate, was increased by P nutrition and increasing growth temperature. Whereas, QPM maize was generally found to perform poorly than normal maize, with respect to phytate content, seed germination and seedling establishment, both cultivars displayed the same responses to phosphorus nutrition and temperature. In both cultivars, globoids, the sites of phytate synthesis and storage, were found only in the embryonic axis. Subsequently, there were significantly low levels of mineral elements (P, Mg and K) found in the endosperm, compared with embryonic axis. This finding suggested that the embryonic axis plays a major role in seed performance, through its effects emanating from phyate metabolism. Myo-inositol plays a role in membrane biogenesis during stress conditions such as temperature by maintaining the integrity of the cell wall and minimizes the leaching of cations essential during germination. Myo-inositol, although it occurs in small concentrations, could be used to indicate seed quality in maize, because its accumulation was found to be associated with enhanced phyate levels and better seed germination in a wide range of temperatures. Low vigour seeds are associated with high electrolyte leakage during imbibition. Mineral elements form a significant portion of the imbibition leachate, which causes seeds to lose nutrients for early seedling growth. This study provided evidence that phosphorus nutrition can alleviate poor seed vigour of maize by improving phytate levels. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

The taro landraces that are most preferred by farmers from Umbumbulu, KwaZulu-Natal were identified through focus group discussions with farmers. Farmers ranked taro landraces on the basis of preference as determined by economic value, social significance, ecological importance and food characteristics. Using pairwise ranking, the farmers' preference of taro landraces across all locations was found to be in the following order: Dumbe-dumbe, Mgingqeni, Pitshi and Dumbe-lomfula. Dumbe-dumbe was identified as the currently actively cultivated taro whereas Mgingqeni was regarded as a less desirable cultivated taro. Pitshi was regarded as an antiquated landrace and Dumbe-lomfula was generally regarded as a taro type of no economic, social or food value that grew on river banks as a wild species. Glasshouse and field studies were conducted to determine the effects of temperature and growing location [Pietermaritzburg (UKZN) and Umbumbulu] on emergence, plant growth and yield of taro. Starch and mineral composition of taro corms were determined in harvest-mature corms. Effects of three day/night temperature levels (22/12°C, 27/17°C and 33/23°C) were examined on the growth of four taro landraces Dumbe-dumbe, Mgingqeni, Pitshi and Dumbe-lomfula. Pitshi-omhlophe, an ecotype of Pitshi for which there was a limited amount of planting material, was also included in the glasshouse studies. The farmers stated that the normal growing season for the economically important landraces, Dumbe-dumbe and Mgingqeni, was six months, but in this study plants were grown in glasshouses for nine months, and in the field, for seven months before the attainment of harvest maturity. Emergence was determined daily for glasshouse experiment until all plants had emerged and it was determined monthly for the field experiment. Leaf number, plant height and leaf area were measured every month to determine growth and development, while number of corms and fresh corm weight were used at harvest to determine yield. For all landraces, time to emergence increased significantly with decrease in temperature from 33/23°C to 27/17°C, but it increased significantly for only Dumbe-dumbe and Mgingqeni from 27/17°C to 22/12°C. Mgingqeni showed the shortest time to emergence, whereas, Pitshi showed the longest delay in emergence. The locations were not significantly different in emergence. Mgingqeni displayed the highest emergence in UKZN (91.4%), whereas, Dumbe-dumbe displayed the highest emergence (95.5%) and Dumbe-lomfula displayed the lowest emergence (55.9%) in Umbumbulu. Leaf number was highest for Pitshi-omhlophe, in glasshouse experiment due to its tendency to produce multiple shoots compared with the other landraces. Plant height increased with increase in temperature for all landraces except for Pitshi, for which height decreased with an increase in temperature. Leaf area was greatest for Dumbe-lomfula at all temperatures and lowest for Pitshi at both 22/12°C and 27/17°C. Leaf number was highest for Mgingqeni and lowest for Dumbe-lomfula at both sites, although it was significantly lower only for Dumbe-lomfula in UKZN. Plant height and leaf area were significantly highest for Dumbe-lomfula at both sites. The highest total number of corms per plant was shown by Pitshi-omhlophe at 22/12°C. Total fresh corm weight was highest for Dumbe-lomfula at 27/17°C and lowest for Pitshi at 22/22°C. The field experiment results showed Pitshi and Dumbe-lomfula with significantly higher total fresh corm weight in UKZN compared with Umbumbulu. Corms were analysed for mineral elements and starch. There were significant differences in starch content between temperatures (P = 0.017) and taro landraces (P = 0.025). There was also a significant interaction of temperatures and landrace (P = 0.002). Starch content increased with temperature for all landraces except for Pitshi-omhlophe and Dumbe-lomfula which showed a decrease at 27/17°C. There were significant differences in corm mineral content between temperatures, locations and landraces (P < 005). It is concluded that the chemical composition of taro corms is influenced by growth temperature and the location (site) where the crop is grown. The results of this study also indicated that taro plant growth is enhanced by high temperatures (33/23°C). High temperatures are, however, associated with short leaf area duration and subsequently low yield. The findings of this study may also be useful in determining taro quality for processing. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

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.

Onions are widely produced within the tropics, but little scientific research has been done specifically on the Eritrean cultivars, like Hagaz Red 1 and 2 (HR I, and HR 2). Many onion cultivars are limited in their range of adaptation due to the combined effects of photoperiod and temperature. A priority for research on the crop was to elucidate the local crop's growth response to environmental conditions, particularly temperature and daylength. The Eritrean cultivars HR I and 2 and an American (Louisiana) cultivar Red Creole (RC) grown in South Africa were grown in growth rooms under all combinations of three daylengths (11.5h, 12h, 12.5h) and three day/night temperatures (25/12°C, 30/15°C and 35/18°C). Growth responses were determined at 108 days and by using a growing degree day (GDD) base. A broken-stick regression model was used to determine the points of inflection, indicating the initiation of bulbing. Based on leaf area and plant height data, mathematical differentiation equations and coefficient of determination (R2) were applied to determine the base temperature (6.4°C) for these particular cultivars. All three cultivars needed at least 12 h daylength for bulb initiation when assessed by a bulbing ratio >=2.0. A bulbing ratio >=2.0 characterizes the onset of bulbing. Under a 11.5 h daylength, a temperature higher than 25/12°C decreased vegetative growth. Temperature in this region may be a supra-optimal condition for the growth of these cultivars at this daylength. However, the 25/12°C and 30/15°C temperatures were found to be ideal for onion bulb production under 12 hand 12.5 h daylengths. The three cultivars (HR I, HR 2 and RC) showed very similar growth response to the daylength and temperature interactions. The thermal presentation of plant growth indicated that there were relationships between bulb initiation and rate of leaf area growth under inductive conditions (12 hand 12.5 h). Under the 12 h daylength, cultivars needed 343, 482, and 597 GDD units before bulb initiation and 405, 432, and 431 GDD to increase the rate of leaf area development at 25/12°C, 30/15°C, and 35/18°C, respectively. Under a 12.5 h daylength, these cultivars needed 344, 423, and 432.2 GDDs to initiate bulbing and 140, 411, and 579 GDDs to increase leaf growth rates at 25/12°C, 30/15°C, and 35/18°C, respectively. In the 12 h daylength, bulbing was initiated and followed by an increased rate of growth of leaf area. However, the reverse happened for the 12.5 h daylength. Overall, where plant response to temperature can be expressed as the rate of progress towards a morphogenetic change, GDD values can be used to predict a plant developmental stage at a particular temperature. It must be concluded that temperatures induced significant variations in growth components (leaf number, plant height, leaf area), and affected bulbing response. The findings in this study confirmed that the cultivars require only a certain fixed amount of thermal time for their development at a particular temperature, and that, if anything, the slow growth rate at the higher temperature must be due to supra-optimal temperatures. They also require a minimum 12 h photoperiod for bulb formation. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

Ethno-archaeological evidence shows that taro [Colocasia esculenta (L.) Schott] originated in Asia. It may have been brought into South Africa a few hundred years after 300 BC from Madagascar, where Malaysian settlers introduced it about 300 BC. The crop is grown in the tropical and subtropical regions of the world, largely for subsistence on farms. In South Africa, taro is mainly produced in the subtropical coastal belt, stretching from Bizana in the Eastern Cape to the KwaZulu-Natal north coast. Although it is a staple crop for the subsistence farmers who grow it, there are no data on taro agronomy in South Africa. The hypothesis of this study was that traditional knowledge about taro production practices is not adequate to form a basis for agronomic and extension interventions to promote the status of the crop to that of a commercial commodity. A survey was conducted at two districts in KwaZulu-Natal, Umbumbulu and Ndwedwe, where taro is a staple crop. The objective of the survey was to determine the cultural practices associated with taro production, including knowledge about varieties, agronomy, plant protection, storage and marketing. Qualitative data obtained from the survey was used to plan an investigation into the agronomy of taro. The survey showed that subsistence farmers at Ndwedwe and Umbumbulu used traditional methods for taro production that had very small influence from the extension services from the Department of Agriculture. The farmers identified three varieties of taro, which they designated as the "red", "white" and "Zulu" types. The "red" and "white" designations were based on consistent crop morphological characteristics. This finding confirmed the reliability of indigenous knowledge for crop classification.The survey also revealed that wetland and dryland conditions are used to produce taro. At Umbumbulu, production occurred predominantly under dryland conditions, whereas at Ndwedwe there was an almost even utilisation of both wetlands and drylands. At both locations, the farmers estimated plant spacing using their feet, which showed that the plant populations would be about 18400 plants ha(-1). Full corms were a predominant type of propagation material. In the light of the survey findings about site types (wetland or dryland), propagation material and plant spacing for taro production, field experiments were designed to 1) determine the effect of site type on taro production, 2) compare three propagule types (full corm, full corm with a shoot and half corm) in taro production and 3) examine the effect of planting density (18400, 24600 and 37000 plants ha(-1) on the performance of propagules with respect to production under wetland and dryland conditions. Field experiments showed that wetland cultivation improved taro yield by 40% compared with dryland production. However, in each of the two site categories, there were significant differences between sites. Using full corms with shoots also enhanced taro yield (42% > full corms without shoots and 66% > half corms), when means were determined across all sites and planting densities. Increasing planting density also caused an increase in taro production (4.9 t ha (-1), 6.8 t ha (-1) and 11.5 t ha (-1), for 18400,24600 and 37000 plants ha,(-1), respectively; LSD (0.05) = 1.4 t ha,1). The enhanced performance of taro under wetland conditions, where corms with a shoot were used and at high planting densities may have been associated with photosynthetic efficiency. Wetland conditions and corms with shoots improved plant emergence and plant growth, which are essential agronomic conditions for efficient capture of the sun's energy for photosynthesis. It is proposed that using propagules with shoots and high plant populations under dryland conditions could enhance taro production. Although wetland cultivation enhanced yield, the survey showed that the total area of land that could be used for wetland cultivation at Ndwedwe and Umbumbulu was too small to warrant sustainable wetland production. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.