Sweet potato SPCP2 is a full-length cDNA isolated from senescent leaves and encodes a putative papain-like cysteine protease. The SPCP2 contained 1101 nucleotides (366 amino acids) in its open reading frame, and exhibited high amino acid sequence identities (ca. 68% to 83%) with plant cysteine proteases, including Actinidia deliciosa, Arabidopsis thaliana, Brassica oleracea, Phaseolus vulgaris, Pisum sativa, Vicia faba, Vicia sativa and Vigna mungo. SPCP2 gene expression was enhanced significantly in natural senescent leaves and in sprouting storage root. Transgenic Arabidopsis plants with ectopic constitutive SPCP2 expression showed earlier floral transition from vegetative to reproductive growth, reduced rosette leaves when flowering, enhanced germination percentage of transgenic progeny seeds in salt-containing MS medium, higher Fv/Fm value, higher relative water content and enhanced tolerance during drought treatment. Based on these results, we conclude that sweet potato papain-like cysteine protease, SPCP2, is a functional gene, and its expression causes altered developmental characteristics and enhances drought and salt stress responses in transgenic Arabidopsis plants.

The sweet potato whitefly is an insect whose economic importance is continually expanding as it becomes a more efficient vector, increases its fecundity and broadens its host range. To keep pace with its ability to develop resistance to existing classes of pesticides, we have undertaken a program to examine the effectiveness of pesticides with novel chemistries and novel modes of action. Several have shown themselves to be very effective against the various life stages of the sweet potato whitefly. Once these are incorporated in to our arsenal of pesticides, we hope to be able to manage resistance by prudently using these new materials.

Populations of the sweet potato whitefly, Bemisia tabaci, have been shown to consist of both migratory and trivial flying morphs. The behavior of these forms as part of the process of short-range migration needed to be examined under field conditions. Insects were marked in a field of cantaloupes using fluorescent dust. During the first growing season traps, used to collect living whiteflies, were placed along 16 equally spaced transects (22.5° apart) radiating out from the field to a distance of up to 0.6 miles. Wind out of the northeast consistently carried migrating whiteflies to traps placed along transects in the southwestern quadrant because cold air drainages dictate wind direction during early morning hours. For this reason, during the second season traps were laid out in a rectangular grid extending 3 miles to the southwest of the marked field. If dispersal was entirely passive or wind directed patterns could be described using a diffusion model. Statistical examination of the data, however, demonstrate that the distribution on all days was patchy. Traps in the immediate vicinity of the marked field caught more whiteflies than the daily median. Large numbers were also collected from around the periphery of the grid. Whiteflies were far less prevalent in the grid's center. As a result, the distribution of captured whiteflies can be described as bimodal. These patterns confirm behavior observed in the laboratory, i.e., a portion of the population are trivial fliers that do not engage in migration and are consequently captured in traps near the field and a portion initially ignore vegetative cues and fly for a period of time before landing in distant traps. This second population comprises the second peak in the model that appeared 1.6 miles from the marked field. On a localized level, 1.6 miles seems to be how far whiteflies move in a day. Earlier studies indicate that whiteflies only fly one day.

Vitamin A deficiency has been recognised as a widespread problem affecting about 750 million people, mostly in developing countries. Mortality due to vitamin A deficiency can be reduced by as much as 23% with improved vitamin A status. Vitamin A's immuneenhancing aspects strengthen the body's defence system against infectious diseases such as measles, malaria and diarrhoea, thus preventing death. Children beyond the weaning age (6 months to 6 years) are most at risk. In South Africa, one in three children has a low vitamin A status, with the rural areas being most affected. Orange-fleshed sweet potato (OFSP) has emerged as a promising plant source with a high beta-carotene content that can make a significant contribution to the vitamin A intake of individuals at risk of vitamin A deficiency. The purpose of this study was to determine the nutrient and sensory quality of OFSP. To this end, the nutrient content of different cultivars of OFSP was determined as well as the sensory characteristics and consumer acceptability was established. During the first phase, four different cultivars of OFSP i.e. Resisto, W119, Jewel and A 15, plus one composite sample, all cultivated by the Agricultural Research Council (ARC)-Roodeplaat, South Africa, were sampled for nutrient analysis. During the second phase (descriptive sensory analysis), four OFSP cultivars and one white-fleshed sweet potato (WFSP) cultivar i.e. Blesbok, were evaluated. A trained sensory panel was used to establish terminology for describing the sensory attributes of the different sweet potato cultivars in terms of its aroma, texture, flavour and aftertaste attributes. Consumer preference (n=180) for OFSP and WFSP was measured by means of a paired preference test. Focus group discussions were conducted to verify findings of the consumer preference test. The results obtained from the nutrient analysis confirmed that OFSP is an excellent source of beta-carotene. A 100 g portion of cooked OFSP can provide up to 6528 ~g beta-carotene, which is approximately 136% of the RDA for vitamin A for children four to eight years. High levels of other nutrients present in OFSP were identified namely vitamin C, calcium and zinc. OFSP further contributes 28% vitamin C, 13% calcium, 15% magnesium and 75.6% zinc of their daily requirements. This study confirms the valuable contribution that OFSP can make as a food-based approach to reduce vitamin A deficiency in individuals at risk. The sensory profiles indicated that OFSP differed from WFSP in colour, flavour and texture. OFSP is generally less moist and subsequently more dense and adhesive compared to WFSP. The latter being more fibrous and less firm than OFSP. Overall OFSP had and earthy aroma which was not typical of WFSP and had a sweeter flavour. The flavour of OFSP was described as similar to that of yellow vegetables such as butternut and pumpkin. Although the different OFSP cultivars had similar characteristics, differences were found in the moist, adhesive and grainy texture attributes as well as the vegetable sweet flavour. Resisto had the sweetest in flavour, with the most dense and pasty texture of the four OFSP cultivars. W119 had the grainiest texture. No significant differences were found in the earthy aroma, sweet potato and yellow vegetable flavour attributes. It can be concluded that in flavour, few differences were found among the OFSP, except in sweetness. OFSP differed primarily from each other in texture. The consumer preference test results showed that overall 85% of respondents preferred the taste of OFSP to that of WFSP, 53% liked the orange colour a lot while 24% liked the colour a little and the remaining 22 % disliked the colour (either a lot, a little, neither like nor dislike). The majority of the consumers (86%) indicated a willingness to buy OFSP. From these results it can be concluded that the taste and colour of OFSP are acceptable to consumers of sweet potato and that it has potential to be successful in the marketplace. Given the high level of consumer acceptability of OFSP, an opportunity exists to address vitamin A deficiency through commercially viable decentralised vine production centres. Such centres could be managed by commercial-, small-scale- and subsistence farmers in South Africa in key sweet potato production areas, with adequate water supply throughout the year. However, availability of commercially produced OFSP in retail sores in recent months, may change this prospect. / Dissertation (MConsSci)--University of Pretoria, 2008. / Consumer Science / unrestricted

The sweet potato has become a major international crop and it is also the main staple food for many people in the developing world. This crop is desirable as it is high yielding, easy to grow and has a low cost of production. However, the tubers have a low protein content and a low concentration of amino acids, particularly the aspartate amino acid. This has contributed to malnutrition in some areas. To help overcome this problem this study had the aim of producing lines of sweet potato with increased nutritional values. Two varieties, Beauregard and LO322, were selected for study as they have a good flavour and a high beta-carotene content. The conditions for the tissue culture of these varieties were determined by altering the mineral and hormonal composition of the culture medium. Increases in nutritional composition were induced by treating calli with mutagenic agents which included : colchicine, ethylmethanesulphonate, UV radiation and two levels of gamma radiation. Putative mutants with reduced feedback inhibition in the pathways which lead to the synthesis of the aspartate amino acids were selected by placing calli on media containing increasing concentrations of lysine and threonine. During the final stage of the selection process, calli were placed on a medium without the addition of selection agents. The results from the tissue culture study suggest that media, 2, 4-D and explant size affect callus growth. MSMA medium (a modified Murashige and Skoog medium) was the most suitable for growing the callus of Beauregard whilst modified White's medium (MW) was better for the growth of LO322 calli. The most prolific callus growth was exhibited by explants of the cultivar Beauregard when placed on MSMA medium. This combination was used to determine the potential of mutagenic treatments to improve the nutritional qualities of the sweet potato. Results from treatments with mutagenic agents showed that all mutagens used had the capability of increasing the soluble protein content of callus. These treatments also had the capacity to increase the concentration of aspartate and other amino acids. Of the mutagens trialed, a treatment with 500 rad gamma radiation appears to be the most suitable for increasing protein and amino acid concentrations. Therefore, once the conditions for regeneration of shoots from calli have been determined this study suggests that it should be possible to produce lines of sweet potato with increased nutritional values using this agent / Master of Science (Hons)

In the past we have assumed that sweet potato whiteflies, Bemisia tabaci (Gennadius), were poor fliers with a limited ability to disperse. This assumption was based on the fact that sweet potato whiteflies are extremely small insects (24 -44 μg) and consequently would be subject to desiccation. We also thought small size would limit their capacity to store sufficient energy reserves to sustain flight for long periods of time. Recent experiments have indicated we were wrong on several counts. Data collected in the laboratory using a vertical flight chamber have revealed a number of interesting facts. Of importance is the fact that a portion of the population is capable of sustaining flight for more than 2.5 hours. In a wind-aided situation, this means they can be moved more than 25 miles in a 10 mph wind. Other details of flight behavior are being made clear to us. For example, we found that flight activity is influenced by host plant quality and age of the whitefly. We hope to eventually be able to predict when whiteflies are going to migrate between crops. This will allow growers to make informed decisions concerning planting dates. We are also working in the field to confirm laboratory results.

No description available.

Master of Science / Department of Human Nutrition / Weiqun Wang / Anthocyanins may prevent chronic diseases such as cancer and cardiovascular disease, however, the anthocyanin metabolites are not well elucidated. We previously selected a purple-fleshed sweet potato clone P40 that contained anthocyanins at up to 7.5 g/kg dry matter, most of which are cyanidin and peonidin derivatives. The main objective of this study is to identify anthocyanin metabolites in the mice fed 20-30% of purple sweet potato P40 (287 mg and 430 mg peonidin-3-glucoside equivalent /kg body weight) diet for 6 weeks. Plasma, liver, and feces were analyzed for anthocyanin metabolites using HPLC/MS and MALDI-TOF-MS. Fifteen hours after consumption of P40 diet, we identified 4 anthocyanin metabolites cyanidin 3,5- diglucoside; cyanidin 3-sophoroside-5-glucoside; cyanidin3-p-hydroxybenzoylsophroside-5-glucoside; and peonidin 3-p-hydroxybenzoylsophroside-5-glucoside in fecal samples. No anthocyanin metabolites were detected in plasma or liver extracts by HPLC/MS or MALDI-TOF-MS. The results indicate that anthocyanin metabolites in fecal samples might provide health benefits for colonic mucosal cells. However, the lack metabolites in both plasma and liver samples suggest a continuous intake of the anthocyanins may be required for systemic benefits due to their quick degradation and low bioavailability.

Temperature and soil moisture (SM) are the two main environmental factors affecting sweetpotato growth and yield. Quantitative functional algorithms of plant growth and developmental processes under a wide range of above factors are needed for developing tools for modeling. Four experiments were conducted to quantify early and late season SM and temperature effects on sweetpotato growth, development, and physiology. In experiment I, effects of five SM levels were evaluated in a greenhouse using cultivars, Beauregard and Evangeline. Experiment II was conducted to evaluate late-season SM effects with four evapotranspiration (ET) based irrigation. In experiment III, five temperatures were imposed at early season (0-59 days after transplanting (DAT)). Late season temperature effects were evaluated with four day/night temperatures from 17 to 91 DAT, in experiment IV. Experiments II, III, and IV were conducted in soil plant atmosphere research facility using Beauregard. Growth, developmental, and physiological parameters were measured. Rate of storage root (SR) development of both cultivars showed a quadratic decline with decreasing SM. Soil moisture optima for SR initiation were 0.168 and 0.199 m3 m-3, equivalent to 63 and 75% field capacity (FC), for cultivars Beauregard and Evangeline, respectively. Shoot biomass declined more rapidly than root with declining SM. Results revealed that, maintaining SM closer to FC during early season is beneficial for early development of root and shoot. Storage root biomass declined quadratically with declining irrigation. The optimum irrigation was 72% of ET and less biomass was partitioned to SRs above that level. Early season temperature study revealed, SR conversion efficiency increased quadratically and reached optimum at 23.9°C with increasing temperature. Maximum rate of SR initiation was reached at 29.5°C in 16.7 d. Biomass partitioned to roots declined linearly with increasing temperature. The SR production efficiency declined from 0.43 to 0.08 g SR kg-1 total weight, and dropped by 81% relative to optimum temperature. The SR fresh weight at high temperature declined 99% relative to optimum temperature. High temperature during mid- and late-seasons partitioned more biomass to shoots, less to roots lowering SR yield. The functional algorithms developed are vital to make management decisions and to develop crop models.

Vitamin A deficiency is recognized as a major health concern worldwide, especially in developing countries. Sweet potatoes are a cash crop that is abundantly grown and available, providing an excellent source of the carotenoid, beta-carotene. Carotenoids are precursors to vitamin A (retinol). Three sweet potato cookie products were developed: glutenree, wheat-containing, and glutenree with extra sweet potato. Products were evaluated by adults and pre-school aged children based on appearance, aroma, texture, flavor, and overall acceptability. Results showed that overall the children liked both the glutenree and wheat-containing cookies (p<0.05). Adults preferred (p<0.05) the glutenree with extra sweet potato and the wheat-containing products. The glutenree cookie contained 10.1 parts per million of beta-carotene as determined by high-performance liquid chromatography.