M. Tech. (Biotechnology, Department of Biosciences, Faculty of Applied and Computer Sciences) Vaal University of Technology / Sweetpotato is one of the most important food crops in developing countries including South Africa. Currently two major types of cultivars are grown in South Africa: one is the orange-fleshed sweetpotato (OFSP) which has high β-carotene content, a precursor of vitamin A. The second type is the cream-fleshed sweetpotato (CFSP) which has low β-carotene content but is high in dry matter. Most South Africans prefer the CFSP although the OFSP offers more advantages. This presents a challenge to plant breeders to develop new varieties that will combine the desirable qualities of both the cultivars. To achieve this goal, plant breeders need knowledge about the genetic variation of the crop to develop an efficient breeding programme. This study assessed the genetic relationships of 28 orange- and cream-fleshed sweetpotato accessions by (i) examining the variation in leaf proteins, (ii) using random amplified polymorphic DNA (RAPD) and, (iii) using variation of the ITS region. The analysis of proteins, RAPD and variation of the ITS region polymorphism levels were 55.6%, 98% and 16.5%, respectively. Dendrograms generated from all the analyses generally clustered the accession according to their flesh colour and country of origin. Analysis of molecular variance (AMOVA) found a significant difference between OFSP and CFSP and a significant difference between the South African and non-South African germplasm. The high genetic diversity in the South African sweetpotato germplasm is a positive indicator for a breeding programme that has a number of targets such as breeding for nutritional improvement, disease resistance and drought tolerance / Hub and Spokes and National Research Foundation (NRF)

Thesis (Ph.D.). / Written for the Dept. of Natural Resource Sciences, Macdonald College of McGill University. Title from title page of PDF (viewed 2008/08/04). Includes bibliographical references.

Doctor of Philosophy / Food Science Institute / Weiqun Wang / Anthocyanins are the most abundant water-soluble flavonoid pigments that are biosynthesized via the phenylpropanoid pathway in plants. Consumption of anthocyanin-rich vegetables and fruits has been linked with multiple health benefits in chronic disease prevention. This dissertation consisted of three studies as follows focused on the profiles and contents of anthocyanins in various sorghum accessions and sweetpotato leaves. Study 1: Sorghum is a rich source of various phytochemicals, but the contents of anthocyanins in various sorghum accessions are not clear. This study was to identify and quantify the anthocyanins by HPLC-DAD in selected 25 sorghum accessions with various phenotypic pericarp pigments. The predominant anthocyanins found in sorghums were 3-deoxyanthocyanidins including the unique leuteolinidin and apigeninidin analogs. The high levels of total anthocyanins were found in the red pericarp PI297139 and the brown pericarp PI221723, followed by the brown pericarp PI35038 and the yellow pericarp PI229838. There were moderate to low levels of anthocyanins observed in all the other accessions except for the white pericarp that generally contained least to undetectable amount. Although anthocyanins appeared to be associated with the pericarp color in the sorghum accessions with the highest contents in each pericarp pigment category, a distinguishable diversity of anthocyanin contents was presented among and between the phenotypic pericarp colors, suggesting other colorful phytochemicals such as carotenoids might be contributed. Establishing a database of anthocyanin profile and diversity in sorghum accessions with various pericarp pigments may lead to the development of novel functional sorghum products with active anthocyanin-enriched health benefits. Study 2: As phytochemical-enriched edible greens, sweetpotato (Ipomoea batatas L.) leaves have become popular. However, the profile and content of phytochemicals in sweetpotato leaves are mostly unknown. We previously bred a purple-fleshed sweetpotato P40 that demonstrated cancer prevention due to high levels of anthocyanins in the tuberous roots. The objectives of this study were to identify and quantify anthocyanins in P40 leaves when compared with the white-fleshed Bonita and orange-fleshed Beauregard. The mature leaves of P40 at 6-week vine stage were collected and extracted for anthocyanin analysis by HPLC-MS/MS. Fourteen anthocyanins, including a novel anthocyanin (peonidin 3-caffeoyl-p-coumaryl sophoroside-5-glucoside), were identified and quantitated. The contents of anthocyanins in P40 leaves (38 ± 2.9 mg/kg DW) were much lower than that in the tubers (13,100 ± 70 mg/kg DW). Furthermore, anthocyanin contents in P40 leaves were even lesser than those of the white-fleshed Bonita (448 ± 50.4 mg/kg DW) and orange-fleshed Beauregard (240 ± 60.9 mg/kg DW). Total phenolic contents as measured by Folin-Ciocalteu were 36.8 ± 4.8 mg GAE/g DW in the leaves of P40, but 46.7 ± 2.1 mg GAE/g DW in Bonita and 41.2 ± 5.0 mg GAE/g DW in Beauregard. No anthocyanin was detectable in the stems of these three sweetpotato varieties. Taken together, this study reports for the first time the profile and content of anthocyanins in the leaves of three sweetpotato varieties with a new anthocyanin identified. The unexpected lower levels of anthocyanins in the purple-fleshed sweetpotato leaves when compared with the tuberous roots advanced our existing database and also validated a diverse phenotype of anthocyanin biosynthesis between sweetpotato leaves and tubers. Study 3: As phytochemical-enriched edible greens, sweetpotato (Ipomoea batatas L.) leaves have potential health benefits. However, how anthocyanin content in sweetpotato leaves responds to harvest stages and growth conditions remains mostly unknown. In this study, we investigated the effect of harvest timing on the accumulation of anthocyanin in the leaves of several sweetpotato varieties: white-skinned and white-fleshed Bonita, red-skinned and orange-fleshed Beauregard, red-skinned and white-fleshed Murasaki, and purple-skinned and purple-fleshed P40. Anthocyanin content increased continuously in Bonita from 1st slip stage to vine stage, but P40 did not have the same response. Beauregard had most anthocyanin (592.5 ± 86.4 mg /kg DW) and total phenolic content (52.2 ± 3 mg GAE/g DW) of mature leaves at vine stage. The P40 variety had low anthocyanin and total phenolic content in the leaves although P40 tubers have the highest among these varieties. In the high tunnel studies, no significant differences in anthocyanin content were found in Beauregard leaves grown in the high tunnels versus the open field. Our study showed for the first time that anthocyanin levels were significantly affected by the growth stages. Our overall results indicate that growth stage and/or environmental factors among sweetpotato varieties affected anthocyanin content, which is highly variable and genotype-dependent. In conclusion, the three studies conducted in this dissertation provided a fundamental understanding of anthocyanin profiles and contents in various sorghum accessions with various phenotypic pericarp pigments and sweetpotato leaves in various growth stages and conditions. These results can be useful not only for the breeders but also consumers in the selection of sorghum accessions and sweetpotato varieties for anthocyanin-contained health benefits.

Pyrethroid and endosulfan mixtures applied at full and reduced rates with three application methods (air-assisted electrostatic, air-assisted hydraulic, and standard hydraulic sprayers) were evaluated in field studies in 1992 and 1993 for control of sweetpotato whitefly, Bemisia tabaci-strain B (Genn.), also known as silverleaf whitefly, Bemisia argentifolii Bellows and Perring, and spray deposition on caulker, Brassica oleracea L. Based on adult suppression, improved control of whiteflies was achieved with full and reduced rates of the air-assisted electrostatic sprayer following two applications in 1992, but percent reduction of adults did not differ significantly among the application methods when full rates of insecticide were applied in 1993. Control based on immature colonization indicated that the air-assisted electrostatic sprayer was the only spray method to significantly reduce nymph densities when compared with the control in 1992, but differences in numbers of eggs, nymphs and eclosed pupal cases varied among application methods and rates of active ingredient in 1993. Comparisons of cauliflower harvest dates indicated that the air -assisted electrostatic sprayer did not provide significantly better control than the other application methods when used at similar rates. Spray deposition with the air-assisted electrostatic application technique was variable throughout these studies with no clear trends being observed. Our results suggest the air-assisted electrostatic sprayer may offer a means to control sweetpotato whitefly with a 50% reduction in insecticide usage.

M. Tech. (Biotechnology, Department of Biotechnology, Faculty of applied and computer sciences) Vaal University of Technolog / Sweetpotato (Ipomoea batatas) is an important food crop that is grown in many countries. A number of viral and fungal sweetpotato diseases have been reported worldwide. One of the major and most economic diseases of the sweetpotato is Alternaria blight which is caused by the fungal pathogen Alternaria bataticola. This disease can be managed in a short term using fungicides and cultural practices. However, a long term and inexpensive approach is through the development of resistant cultivars. A prerequisite to this approach is the knowledge of the genetic diversity of this fungal pathogen. This study assessed the genetic diversity of 25 South African isolates of A. bataticola from naturally infected leaves and stems collected from different sweetpotato growing regions in South Africa by (i) characterising the isolates based on their morphology (ii) pathogenicity tests (iii) random amplified polymorphic DNA (RAPD) (iv) variation of the ITS2 sequences and (v) prediction of the ITS2 secondary structures. The isolates revealed some variation in colony colour pigments after culturing but Koch’s postulates were confirmed by their pathogenicity tests. The analysis of RAPD and variation of the ITS2 sequences showed high levels of variation (100%) among the isolates. Dendrograms generated from these analyses had many subclusters and did not cluster the isolates according to their geographic origins. The ITS2 secondary structures were predicted and can be used to identify and distinguish the isolates. This information in addition to the genetic diversity of the A. bataticola isolates will aid plant breeders in the development of resistant sweetpotato cultivars and early management of blight disease in South Africa.

Three distinct plant viruses, transmitted by the tobacco whitefly Bemisia tabaci Genn., were associated with diseased food or fiber crops grown in the southwestern deserts of Arizona. The cotton leaf crumple virus (CLCV), thought to affect only cotton Gossypium (L.) spp., is now known to infect other malvaceous plants and members of the Convolvulaceae and Leguminosae. Results of an experimental host range study suggest that potential virus-vector reservoirs may exist in cotton growing regions which include both weeds and cultivated plants. Geminivirus-like (GVL) particles of ∼18 x 30 nm were isolated for the first time from CLCV-infected bean, Phaseolus vulgaris (L.), 'Red Kidney', a plant which was a better purification host than cotton. Studies of CLCV-vector relationships indicated that the acquisition- and inoculation-access times, latent period and length of retention by whitefly vectors were similar to those of the original isolate reported in California in 1954. When growth chamber temperatures of 26, 32, and 37C were used in virus-vector studies, optimal acquisition and transmission occurred at 32C while temperatures of 37C were lethal to whitefly adults. Two additional virus-like agents were isolated from single and mixed infections of lettuce or melons, respectively. The virus-like agent from lettuce infected primarily members of the Chenopodiaceae, Compositae and Cucurbitaceae, and was whitefly but not mechanically transmissible. Long flexuous closterovirus-like rods of ∼10 x 1400-2000 nm were visualized in extracts prepared from plants inoculated with the lettuce isolate. The isolate was similar to the lettuce infectious yellow virus (LIYV) based upon host range, transmission characteristics and unique particle morphology. Both long flexuous rods like those associated with the lettuce isolate and GVL particles of 18 x 30 nm were associated with diseased melons. The host range of the GVL agent was confined to the Cucurbitaceae and Leguminosae and the agent was separated from the mixed infection by mechanical transmission to a non-LIYV host. The GVL-agent was distinct from previously described cucurbit viruses including the squash leaf curl virus, based upon host range and transmission characteristics and was tentatively designated as the watermelon curly mottle virus (WCMV).

Para mejorar la eficiencia de regeneración en dos variedades africanas de camote (Tanzania y Wagabolige) se probó un protocolo vía organogénesis de dos fases en Tanzania y de dos, tres y cuatro fases en Wagabolige. La primera fase, en ambas variedades, consistió en el mantenimiento de los explantes en un medio con auxinas y las siguientes, con citoquininas. Se probó tres tipos de explantes: hojas con peciolo, peciolos y raíces. Todos los regenerantes fueron obtenidos a partir de hojas con peciolo. Los brotes emergentes fueron de apariencia normal y anormal. Se logró resultados favorables al trabajar con bajas concentraciones de 2,4-D y en Tanzania, al suplementar AG3 a la primera etapa, se incrementó la frecuencia de regeneración de brotes normales; sin embargo, ambas variedades presentaron un bajo índice de regeneración: 3.33% en Tanzania y 1.46% en Wagabolige.To improve the regeneration efficiency of two sweetpotato African varieties (Tanzania and Wagabolige), a two-stage organogenesis regeneration protocol was tested in Tanzania; while a two, three, four-stages was tested in Wagabolige. The first stage, in both varieties, maintained the explants in a medium supplemented with auxines, and the next stages, with cytokinines. Three different explants were tested: leaves with petiole, petioles and roots. All shoots came from leaves with petioles. Shoots presented normal or anomalous morphology. The best results were obtained working with low concentrantions of 2,4-D. For Tanzania, the addition of GA3 in the first stage was found to increase normal shoot frequency, nevertheless both varieties showed low regeneration efficiencies: 3.33% in Tanzania, and 1.46% in Wagabolige.

Sweetpotato (<i>Ipomoea batatas</i>) is a popular vegetable across the world. It is a staple food item of many countries in South America, Africa and Asia where the population depends on the crop as an important source of energy and essential nutrients like vitamins A and C, calcium, iron and copper. It is also a very popular crop in North America. Deep fat frying is one of the favourite processing methods for sweetpotato. The method is fast and the finished product is desired for its unique flavour and taste. <p>The main objective of this study was to establish analogy between convective heat and mass transfer during frying. The accurate estimation of the coefficients for both phenomena is challenging. During frying, the rate of heat transfer from the oil to the food surface is largely controlled by the convective heat transfer coefficient. This heat transfer coefficient is dependent on the interaction between the temperature gradient and the drying rate in a frying process. The temperature gradient and the drying rate in turn partly depend on the thermophysical properties of the product. In this study, thermophysical properties of sweetpotato were studied and modeled as a function of moisture content and temperature. The properties of interest are specific heat capacity, thermal conductivity, thermal diffusivity and density. A designed deep fat frying experiment of sweetpotato was carried out under four different oil temperatures (150, 160, 170 and 180°C) and using three different sample sizes (defined as ratio of diameter to thickness (D/L: 2.5, 3.5 and 4.0). Convective heat transfer coefficients under these frying conditions were estimated and computer simulation based on finite element modeling technique was used to determine convective mass transfer coefficients. Correlation between heat transfer coefficient and mass transfer coefficient were investigated with reliable statistical tool. Effects of sample size, oil temperature and frying time on heat and mass transfer were also studied. <p>Specific heat, thermal conductivity and thermal diffusivity of sweetpotato were all found to increase with increase in temperature and moisture content. Density decreased with increase in moisture content. Maximum heat transfer coefficient reached during sweetpotato frying was in the range of 700-850 W/m2.°C. Heat transfer coefficient of sample during frying increased with increase in frying oil temperature but decreased with increase in sample size. Same trend for heat transfer coefficient was observed for effects of oil temperature and sample size on mass transfer coefficient. Maximum mass transfer coefficient reached during sweetpotato frying was in the range of 4×10-6 to 7.2×10-6 kg/m2.s. No general relationship was established between heat transfer coefficient and mass transfer coefficient during frying but a relationship was established between maximum heat transfer coefficient and maximum mass transfer coefficient. A trend was also observed between maximum heat transfer coefficient and the corresponding mass transfer coefficient at that point.

Sweetpotato (<i>Ipomoea batatas</i>) is a popular vegetable across the world. It is a staple food item of many countries in South America, Africa and Asia where the population depends on the crop as an important source of energy and essential nutrients like vitamins A and C, calcium, iron and copper. It is also a very popular crop in North America. Deep fat frying is one of the favourite processing methods for sweetpotato. The method is fast and the finished product is desired for its unique flavour and taste. <p>The main objective of this study was to establish analogy between convective heat and mass transfer during frying. The accurate estimation of the coefficients for both phenomena is challenging. During frying, the rate of heat transfer from the oil to the food surface is largely controlled by the convective heat transfer coefficient. This heat transfer coefficient is dependent on the interaction between the temperature gradient and the drying rate in a frying process. The temperature gradient and the drying rate in turn partly depend on the thermophysical properties of the product. In this study, thermophysical properties of sweetpotato were studied and modeled as a function of moisture content and temperature. The properties of interest are specific heat capacity, thermal conductivity, thermal diffusivity and density. A designed deep fat frying experiment of sweetpotato was carried out under four different oil temperatures (150, 160, 170 and 180°C) and using three different sample sizes (defined as ratio of diameter to thickness (D/L: 2.5, 3.5 and 4.0). Convective heat transfer coefficients under these frying conditions were estimated and computer simulation based on finite element modeling technique was used to determine convective mass transfer coefficients. Correlation between heat transfer coefficient and mass transfer coefficient were investigated with reliable statistical tool. Effects of sample size, oil temperature and frying time on heat and mass transfer were also studied. <p>Specific heat, thermal conductivity and thermal diffusivity of sweetpotato were all found to increase with increase in temperature and moisture content. Density decreased with increase in moisture content. Maximum heat transfer coefficient reached during sweetpotato frying was in the range of 700-850 W/m2.°C. Heat transfer coefficient of sample during frying increased with increase in frying oil temperature but decreased with increase in sample size. Same trend for heat transfer coefficient was observed for effects of oil temperature and sample size on mass transfer coefficient. Maximum mass transfer coefficient reached during sweetpotato frying was in the range of 4×10-6 to 7.2×10-6 kg/m2.s. No general relationship was established between heat transfer coefficient and mass transfer coefficient during frying but a relationship was established between maximum heat transfer coefficient and maximum mass transfer coefficient. A trend was also observed between maximum heat transfer coefficient and the corresponding mass transfer coefficient at that point.

Master of Science / Department of Horticulture and Natural Resources / Jason Griffin / Cary L. Rivard / Sweetpotatoes [Ipomoea batatas (L.) Lam.] are nutritious, easily stored and marketed, well-adapted to organic production, and fit large or small farming operations. Commercial production of propagules for sweetpotato, vine cuttings known as slips, is concentrated among a few coastal states. Consequently, growers in the Central United States have limited access to planting material. Considering the crop’s sensitivity to cold climates and the increasing use of high tunnels (HTs) in the region, the implementation of HT production systems could be a viable mechanism for increasing the distribution of sweetpotato nurseries across the US. The goal of this project was to investigate the production of slip propagation beds in HT systems at two research stations in Northeast and South Central Kansas. Trials were conducted in 2016 and 2017 to compare yield and quality of organic slips grown in HTs and the open-field (OF). Additionally, a split-plot design was utilized inside the HT to compare slip yields for three planting densities (45, 65 and 85-seed roots/m²). Slips grown in the two systems (HT and OF) were field-planted to elucidate the impact of the system on subsequent root tuber yields and grade. HT enterprise budgets were developed to determine what the potential economic impact is for growers that wish to implement this system and to identify the appropriate planting density based on cost and return. In 2016, the HT plots produced more slips than in the OF (P < 0.05), and the overall average slip number was 226.7 in the HT and 147.8 in the OF across both years. However, slips grown in the HT had significantly fewer nodes, less foliage, and compactness (P < .001). The field performance study showed slightly greater average marketable storage root yield from slips produced in the OF (P = NS), but the quantity and distribution of graded storage roots were similar between slips grown in the HT and OF treatments. Increased planting density treatment corresponded with greater average slip yield across all harvests, but was only statistically significant during 1st harvest of 2016. The positive correlation between slip yield and planting densities plateaued between 65 and 85-seed roots/m². When using foundation seed roots the optimum profit for enterprise budgets was achieved at the 65-seed root planting density. The use of 25% foundation and 75% on-farm produced seed roots at 85-seed root density generated $1.05/ft² profit in HT—using the more manual cultural practices and equipment of two case studies. The results of these trials suggest that slip production in HTs may provide growers in the Central and Northern regions of the U.S. a viable technology for developing their own sweetpotato propagation schedule, without compromising plant yield or storage root production. When compared to other common HT crop budgets, our data suggest that HT slip production is an economically-viable system for growers who wish to incorporate slip propagation beds into their HT rotations.