Proefschrift--Wageningen. / Bibliographies: p. 265-288.

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Milling data from sugar factories in Mauritius were examined from 1960 to 2004 to assess the trend in the quality of cane received at mills and the change in factory performance. A deterioration in overall quality was apparent due to the increased level of extraneous matter delivered in the cane supply. Comparison was made with available data from other countries in the world, notably those of South Africa and Australia. Controlled addition of extraneous matter to clean cane was effected under laboratory conditions to determine the relative impact of dry leaves, green leaves and cane tops on the quality of cane and the resulting juice, and to predict through derived equations, their impact on cane processing. The addition of dry leaves was found to have the most adverse effect followed by green leaves and cane tops. In the case of dry leaf addition to cane the detrimental effects were found to be masked by an increase in the concentration of solutes in the juice extracted. This phenomenon was thought to be due to the selective sorption of water (so-called Brix-free water) by dry leaves. To test this assertion, the sugar cane stalks of four different cane varieties aged 52, 44 and 36 weeks were separated into their component parts by means of a method devised in this work. There were nine component parts: stalk fibre, stalk pith, rind fibre, rind fines, top fibre, dry leaf fibre, dry leaf fines, green leaf fibre and green leaf fines which, on characterisation by Fourier transform infrared spectroscopy and scanning electron microscopy, were very similar except that stalk pith was more flaky and had a higher surface area than the others. Various analytical techniques were tested for the determination of Brix-free water. The most convenient method proved to be a refractometric method which was improved so as to be applicable to the wide range of cane components fibres studied. Statistical analysis of the Brix-free water content of the separated samples showed that when the combined effect of fibre and pith in the cane stalk of three ages was considered, the four cane varieties were not different. This was not the case for dry leaf, green leaf, top and rind. Of the nine cane components, stalk pith exhibited the highest Brix-free water value of about 20 g/100 g fibre, whereas all the other components exhibited values of about 15 g/100 g fibre, which are much lower than the traditionally accepted value of 25% for cane. The latter was found to be the fibre saturation point of bound water determined at 20 oC, which is the sum of dissolved and hydrated waters, and which is normally greater than the Brix-free water value as determined in this work. The water sorption characteristics of the various cane component parts were further investigated by making measurements to determine the equilibrium moisture contents at various water activity values. These data were used to construct adsorption isotherms. These were fitted to 17 existing isotherm models, of which two, namely, the Hailwood-Horrobin and Guggenheim-Anderson-de Boer models, gave the best fit. The sorbed water was subsequently characterised in terms of various parameters, namely, the monolayer moisture content, the number of adsorbed monolayers, the percentage of bound water, the total surface area for hydrophilic binding, the heats of sorption of the monolayer and multilayers, the net and total isosteric heats of sorption and the entropy of sorption. From the monolayer moisture content and the amount of “hydrated water” as calculated from the Hailwood-Horrobin model, it is clear that at EMC values between 0 and 5% (aw = 0 – 0.3), the non-freezable water is tightly bound to the surface of the fibre. The second region starts at EMC values from 5% to 10 – 15% (aw = 0.3 to 0.6 – 0.8) depending on the cane components, and the bound water in this region is termed the freezable water. The third type of water is essentially free water, it exists after the second region and ends at EMC values of about 25%. From this study, it is apparent that the Brix-free water as measured in this work measures the amount of water bound in the first two regions. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2008.

South Africa is the leading producer of sugarcane in Africa and one of the largest sugarcane producers in the world. Sugarcane is grown under a wide range of climatic, agronomic, and socio-economic conditions in the country. Stress factors such as water and nutrient deficiencies, and insect pests and diseases are among the most important factors affecting sugarcane production in the country. Monitoring of stress in sugarcane is therefore essential for assessing the consequences on yield and for taking action of their mitigation. The prediction of sugarcane yield, on the other hand is also a significant practice for making informed decisions for effective and sound crop planning and management efforts regarding e.g., milling schedules, marketing, pricing, and cash flows. In South Africa, the detection of stress factors such as nitrogen (N) deficiency and sugarcane thrips (Fulmekiola serrata Kobus) damage and infestation are made using traditional direct methods whereby leaf samples are collected from sugarcane fields and the appropriate laboratory analysis is then performed. These methods are regarded as being time-consuming, labour-intensive, costly, and can be biased as often they are not uniformly applied across sugarcane growing areas in the country. In this regard, the development of systematically organised geo-and time-referenced accurate methods that can detect sugarcane stress factors and predict yields are required. Remote sensing offers near-real-time, potentially inexpensive, quick and repetitive data that could be used for sugarcane monitoring. Processing techniques of such data have recently witnessed more development leading to more effective extraction of information. In this study the aim was to explore the potential use of remote sensing to quantify stress in and predict yield of sugarcane in South Africa. In the first part of this study, the potential use of hyperspectral remote sensing (i.e. with information on many, very fine, contiguous spectral bands) in estimating sugarcane leaf N concentration was examined. The results showed that sugarcane leaf N can be predicted at high accuracy using spectral data collected using a handheld spectroradiometer (ASD) under controlled laboratory and natural field conditions. These positive results prompted the need to test the use of canopy level hyperspectral data in predicting sugarcane leaf N concentration. Using narrow NDVI-based vegetation indices calculated from Hyperion data, sugarcane leaf N concentration could reliably be estimated. In the second part of this study, the focus was on whether leaf level hyperspectral data could detect sugarcane thrips damage and predict the incidence of the insect. The results indicated that specific wavelengths located in the visible region of the electromagnetic spectrum have the highest possibility of detecting sugarcane thrips damage. Thrips counts could also adequately be predicted for younger sugarcane crops (4–5 months). In the final part of this study, the ability of vegetation indices derived from multispectral data (Landsat TM and ETM+) in predicting sugarcane yield was investigated. The results demonstrated that sugarcane yield can be modelled with relatively small error, using a non-linear random forest regression algorithm. Overall, the study has demonstrated the potential of remote sensing techniques to quantify stress in and predict yield of sugarcane. However, it was found that models for detecting a stress factor or predicting yield in sugarcane vary depending on age group, variety, season of sampling, conditions at which spectral data are collected (controlled laboratory or natural field conditions), level at which remotely-sensed data are captured (leaf or canopy levels), and irrigation conditions. The study was conducted in only one study area (the Umfolozi mill supply area) and very few varieties (N12, N19, and NCo 376) were tested. For practical and operational use of remote sensing in sugarcane monitoring, the development of an optimum universal model for detecting factors of stress and predicting yield of sugarcane, therefore, still remains a challenging task. It is recommended that models developed in this study should be tested – or further elaborated – in other South African sugarcane producing areas with growing conditions similar to those under which the predictive models have been developed. Monitoring of sugarcane thrips should also be evaluated using remotely-sensed data at canopy level; and the ability of multispectral sensors other than Landsat TM and ETM+ should be tested for sugarcane yield prediction. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Sugarcane has become an increasingly important crop in recent years, with South Africa featuring as one of the prominent producers. This has led to a significant growth in the South African sugarcane industry, translating into an increased demand for planting material. Although this demand is now satisfied by recent biotechnological advancements such as protocols for somatic embryogenesis to increase the production of planting material, such techniques are limited as a result of the progressive loss of the embryogenic potential of calli over time. In order to facilitate management of this material, it is desirable to develop a protocol for the long-term storage of the germplasm. This study reports on investigations of the different parameters that influenced the cryoprocess in attempts to develop a protocol for the successful cryopreservation of sugarcane somatic embryos of the 88H0019 variety. Experiments were carried out to determine in vitro culture conditions for successful induction of somatic embryos via both the direct and indirect routes of micropropagation. A suitable regeneration medium for plantlet establishment pre- and post-cooling was established (Chapter 2). Investigations were also carried out to ascertain the responses of somatic embryos to both rapid and slow dehydration techniques (Chapter 3). Finally, several cooling techniques (both slow and rapid), were applied, on partially dehydrated somatic embryos, either without, or after cryoprotection, in an attempt to achieve survival after cryopreservation of the somatic embryos (Chapter 4). Both directly- and indirectly-derived somatic embryos were converted, most successfully, on full strength Murashige and Skoog medium without addition of plant growth regulators. The initial mean water contents of directly- and indirectly-derived somatic embryos were not significantly different from each other (8.38±0.19 g g-1 and 8.45±0.33 g g-1 [dry mass basis], respectively). The percentage conversion at these water contents was also not significantly different; 97% for directly- and 98% for indirectlyinduced embryos. Slow dehydration by culture on a series of media with increasing concentrations of sucrose (from 0.2 M to 1.2 M) for a period of 48 h each was the most effective technique, with water content being reduced to 0.94±0.03 g g-1 and 0.95±0.02 g g-1 after dehydration on media containing 1.0 M sucrose, while maintaining between 98% and 100% conversion, respectively. Of the various cryoprotectants tested, proline and casamino acid had the least adverse effects on the somatic embryos. The encapsulation-vitrification cooling technique was the most efficient of all techniques employed. The best conditions involved encapsulation of embryo clumps in a solution of MS medium with 3% (w/v) Na-alginate and loading solution containing 2 M glycerol plus 0.4 M sucrose, followed by infiltration and dehydration at 0°C for various time intervals (0, 5, 10, 15, 20, 25, 30 min) with 1 ml PVS2 solution and thereafter, rapid immersion in liquid nitrogen. Under such conditions, 30% of the cryopreserved somatic embryos retained viability, going on to form callus from which shoots and roots were produced. Although somatic embryos of sugarcane of the local variety 88H0019 have proved to be recalcitrant to cryopreservation, the results obtained with explants that had been processed by encapsulation-vitrification suggest that this approach may be worth pursuing and refining. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2009.

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Thesis (Ph. D.)--University of Hawaii at Manoa, 1991. / Includes bibliographical references (leaves 112-124) / Microfiche. / xiv, 124 leaves, bound ill. 29 cm

Thesis (Ph. D.)--University of Hawaii at Manoa, 1995. / Includes bibliographical references (leaves 227-240). / Microfiche. / xvi, 240 leaves, bound ill. 29 cm

Typescript. / Bibliography: leaves [223]-228. / xiv, 228 l graphs, tables