Sweetpotato (Ipomoea batatas (L.) Lam.) is an important food crop in East Africa including Kenya. The crop incurs high yield losses in production due to biotic (insect pests and diseases) and abiotic (drought, and heat) constraints. Among abiotic constraints, drought is the most important. Prolonged periods of drought in arid and semi-arid areas of Kenya have led to reduced quantity and quality of sweetpotato storage roots and in severe cases caused total crop failure. The objectives of this study were to: 1) determine sweetpotato production system constraints and farmers’ coping strategies; 2) evaluate sweetpotato clones for yield performance and drought tolerance; 3) analyse genotype x environment interaction and stability for storage root yield of selected clones, 4) determine mechanisms of drought tolerance in sweetpotato, and 5) determine combining ability and heterosis for yield and drought tolerance traits under managed drought stress conditions. To determine the production constraints and farmers’ coping strategies, a survey was conducted in central, eastern and western Kenya. Out of 345 farmers interviewed, 60% were women, and 40% men. Farm sizes ranged from 0.4-0.8 ha, with 90% of sweetpotato cultivated on 0.2 ha or less. The main sweetpotato varieties were Vitaa, Kabonde and Bungoma and the majority of farmer’s used their own conserved planting material which was conserved by leaving them in the field after harvest. About 35% of the farmers identified weevils as the major pest, and sweetpotato virus disease (SPVD) as the major disease, while 28% of the farmers identified drought as a major constraint. The farmers used clean seed, high yielding varieties, high planting density, and manure application as the main strategies to cope with sweetpotato production constraints. Eighty four sweetpotato clones were evaluated under managed drought stress environments at KARI-Kiboko and KARI-Thika. Drought reduced the fresh weight of storage roots (FSR) (72.5%), fresh biomass weight (FB) (74.0%), marketable fresh storage root (MFSR) (80.7%), number of storage roots (NSR) (24.5%), days to permanent wilting point (DPWP) (0.3%), but seemed to increase percent root dry matter (% RDM) (-4.7%), harvest index (HI) (-2.6%), and chlorophyll content (CC) (-2.7%). Across the environments, genotypes 194555.7 (1.06), 421066 (1.05), Chingovu (0.94), 420014 (0.91), Excel (0.9), 199062.1 (0.87) and Unawazambane06-01 (0.81) gave higher FSR yields (kg plant-1) than the local checks. Genotypes Nyarmalo and Polista were among the lowest yielding in the irrigated and non-irrigated conditions. Clones W119, 441725, and Xiadla-xa-kau were the highest yielding under the drought stress conditions. The performance of 24 improved clones was evaluated in replicated trials at KARI-Thika and KARI-Kiboko using 24 sweetpotato clones grown under managed drought stress conditions for two seasons. AMMI, GGE biplots and regression analyses were conducted to determine stability of the clones. Mean FSR was significantly different (P < 0.001) in the two research sites with the environment contributing to 92.7% of the total variation, genotype 1.8%, and interactions 0.4%. AMMI and GGE biplots, and regression indicated the most stable clones to be 441725, Unawazambane06-01 and 189150.1, while Xiadla-xa-kau was the least stable. To gather more information on drought tolerance mechanisms expressed in the sweetpotato genotypes, an experiment was conducted in the greenhouse using clones expressing different levels of drought tolerance in the field. The results showed more under-developed roots (pencil roots) in the drought stressed regimes than in the irrigated regimes and in the drought susceptible genotypes. Drought tolerant genotypes produced more FSR and NSR. The number of vine branches (NVB), vine tip pubescence (VTP) and mature leaf pubescence (MLP) increased with reduction of drought stress however, drought tolerant clones had reduced NVB. Drought stressed clones had shorter basal vine length (BVL), reduced CC, and reduced leaf growth (LG). Drought stress reduced growth of vines in terms of internodes length, internodes diameter, vine length, petioles length, and leaf CC. Overall, for the first time, the study demonstrated that drought stress in the first three months after planting, leads to the proliferation of non-edible pencil roots, which do not become edible storage roots even when drought stress is removed. Therefore, water is critical during this period for improved sweetpotato storage root yield, probably as a drought tolerant mechanism. Combining ability for yield and drought tolerance of 15 F1 sweetpotato families generated through a half diallel mating of six parents was evaluated at KARI-Kiboko in 2012. Significant (P≤0.05) general combining ability (GCA) and specific combining ability (SCA) effects were recorded for root yield in both drought stress and no stress conditions, indicating that both additive and dominance gene effects were important in the inheritance of resistance to drought stress. Progenies from families G2, G5, G7, G8, G10, G12 and G15 had good SCA for fresh storage root yield, total biomass, number of days to permanent wilting point (DPWP), harvest index, and drought stress index (DSI). Progeny 8 from family G4, 5 and 8 from G15, had the highest mid and best parent heterotic effect (117-270%) for fresh storage root yield in both drought stress and no stress conditions. Progeny 6, and 7 from family G10, had the highest mid and best parent heterotic effect (165-234%) for fresh total biomass yield under no drought stress conditions. In conclusion, the progenies from families G2, G5, G7, G8, G10, G12 and G15 that had high yield and biomass specific combining ability under drought and no drought stress indicated that they could be having drought tolerant genes, and therefore could be incorporated into advanced drought screening trials with the aim of releasing the best performing drought tolerant varieties. Secondly, the findings in this study lay a foundation for sweetpotato breeding programmes on drought tolerance. Thirdly, for the first time, this study uniquely combines yield performance, combining ability estimates, days to permanent wilting point and heterosis under contrasting moisture regimes to unmask the gene action of drought tolerance in sweetpotato, a milestone in science. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Alternaria leaf petiole and stem blight is an important disease of sweetpotato (Ipomoea batatas (L.) Lam.) causing yield losses in both landraces and improved cultivars. The most important species causing economic yield loss in Uganda are Alternaria bataticola and A. alternate with A. bataticola the most aggressive and widely distributed. The study was conducted to: i) establish farmer-preferred sweet potato attributes, production constraints and Alternaria leaf petiole and stem blight awareness; ii) evaluate Ugandan sweet potato germplasm for Alternaria leaf petiole and stem blight resistance; iii) determine the mode of inheritance of resistance to Alternaria leaf petiole and stem blight and storage root yield components of sweet potato through estimation of the general combining ability (GCA) of the parents and the specific combining ability (SCA) of the parents for each cross; and iv) determine the adaptability and farmer acceptability of selected F1 genotypes across environments. The participatory rural appraisal was conducted to establish farmer preferences and production constraints revealed that farmer preferred sweet-potato traits were high yield, sweetness (taste), early maturity, high dry mass, resistance to pests and diseases, and in-field root storability after maturity. A majority of the farmers considered Alternaria leaf petiole and stem blight a serious production constraint causing yield loss of over 50%. The main control measures against the disease were roguing of infected plants, spraying with fungicides, use of healthy planting materials and planting resistant genotypes. Thirty sweet potato land races and improved cultivars were evaluated for Alternaria blight severity; yield, dry mass, harvest index, sweetpotato weevil (Cylas spp.) damage and sweetpotato virus disease at two sites (Namulonge and Kachwekano) over three seasons (2010B, 2011A, 2011B) under Alternaria inoculum and fungicide spray treatments. Landrace Shock was more resistant to Alternaria blight than Tanzania, the resistant check. Genotypes NASPOT 1, NASPOT 7, New Kawogo and Dimbuka were the most susceptible. Thirty two F1 families were generated from 16 parents in two sets in a North Carolina II mating scheme. The families were evaluated at two sites using a 5 x 7 row-column design with two replications. There were significant (P<0.05) differences among the families in Alternaria blight severity. Both GCA and SCA mean squares (MS) for Alternaria blight were highly significant (P<0.001) but the predominance of GCA sum of squares (SS) for Alternaria blight at 67.4% of the treatment SS versus 32.6% for SCA SS indicated that additive effects were more important than the non-additive effects in controlling this trait. For the yield components, the GCA MS were significant (P<0.05) and accounted for more than 60% of the treatment SS except for percentage dry mass composition where SCA SS accounted for 53.0% of the treatment SS implying that non-additive genetic effects were slightly more important than additive for this trait. Some parents that had desirable high, negative GCA effects for Alternaria blight produced families with undesirable positive SCA effects and the reverse was also true. This implied that the best parents should not be chosen based on GCA effects alone but also on SCA effects of their best crosses. The promising F1 genotypes selected from previously evaluated crosses together with one Alternaria blight resistant check (Tanzania) and one susceptible check (NASPOT 1) were evaluated at three sites (Namulonge, Kachwekano and Serere) using a randomised complete block design with three replications. Scientists and farmers evaluated the agronomic performance and also quality traits of the genotypes before and at harvest. Genotypes G14, G16, G24, G29, G49, G59 and G69 were the most stable across the sites for low Alternaria blight severity and can, therefore, be recommended for further evaluation under both low and high disease pressure areas. Genotypes G67, G13, G14, G24, G29 and G53 were the most high yielding and stable across the sites and were therefore the most widely adapted. In the participatory selection, before harvest and at harvest, Spearman’s rank correlation of the scientists and farmers’ mean ranking of the genotypes at each site was positive and significant. This indicated that the scientists in the study were capable of selecting for farmer preferred traits. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Sweetpotato (Ipomoea batatas, L.) is one of the important sources of carbohydrates and economic income in Mozambique. As with most of the food crops in Mozambique, it is usually produced by small-scale farmers under dryland conditions. Despite the importance of the crop, the storage root yields are still low and it is difficult to keep planting material (vines) for the next planting season. One of the major challenges to production is drought stress. Drought stress affects sweetpotato by retarding aboveground growth, reducing total root yield, percentage of dry mass, and reducing the quality of the roots as a result of the increase in damage caused by the sweetpotato weevil (Cylas formicarius). The objective of this study was to identify sweetpotato genotypes tolerant to drought particularly amongst the orange fleshed types which can be used in breeding programmes to improve the drought tolerance of genotypes grown in Mozambique. To this end, 48 genotypes were evaluated in both field and greenhouse studies conducted at Umbeluzi Research Station (26º 03’ S, 32ºC 23’ E; 12 masl) located about 30 km from Maputo city. The field trial was a three replicate, α-design with split-plots. Genotypes were the wholeplot treatment factor and irrigation levels were the sub-plot treatment factor. The three irrigation levels imposed were: nonstressed plants irrigated from planting to 120 DAP; moderately stressed, plants irrigated until 60 DAP; and severely stressed, plants irrigated until 30 DAP. In the greenhouse trial the 48 genotypes were grown in wooden boxes arranged in a two replicate, randomized complete block design. The plants were exposed to water stress from 10 DAP to the end of experiment at 60 DAP. Genotypes were significantly different for all traits, namely: survival %, vine vigour, aboveground biomass, total and commercial root yield, total fresh biomass, harvest index, β-carotene content, % dry mass, dry mass yield, incidence of sweetpotato virus disease, and incidence of weevil damage. Irrigation levels were significant for the traits: survival %, vine vigour, aboveground biomass, total and commercial root yield, total fresh biomass, harvest index, β-carotene content, % dry mass, and dry mass yield. Irrigation levels were not significant for incidence of sweetpotato virus disease and incidence of weevil damage. The genotypes x irrigation levels interaction was significant for: total and commercial root yield, and incidence of weevil damage; and not significant for: survival %, vine vigour, aboveground biomass, total fresh biomass, harvest index, β-carotene content, % dry mass composition, dry mass yield and incidence of sweetpotato virus disease. The mean dry mass yields across irrigation levels of the national breeding lines and introduced genotypes were higher than the landrace genotypes. Most of the national breeding lines had higher β-carotene content than the introduced and landrace genotypes. The landrace genotypes had relatively higher % dry mass composition compared to the national breeding lines. The stress tolerance index (STI) separated the 48 sweetpotato genotypes evaluated in the field trial into three groups: drought tolerant (high STI); moderate drought tolerant (intermediate STI); and drought sensitive (low STI). Under moderate stress, yield potential (Yp) and yield in a stress environment (Ys) were highly significant, positively correlated with Mean productivity (MP), Geometric mean productivity (GMP), Stress tolerance index (STI) and Tolerance index (TOL). Under severe stress the same correlations were reported. Under moderate and severe stress, the correlation between stress tolerance index (STI) and Stress susceptibility index (SSI) was significant and negative. In the greenhouse trial, differences between genotypes in vine length increment, vine diameter increment, leaf width increment and number of nodes vine-1 were significant (P<0.05). Vine length, vine diameter, leaf width and length increments either increased or were reduced due to water stress. Less than 10% increment in vine length (between 25 and 50 DAP) was recorded in MGCl01, Atacama, Cordner, Beauregard, and CN1448-49. Higher than 40% vine length increment was recorded in Jonathan and UNK-Malawi, Naspot, MUSG0614-24, Resisto, K566632, Tainung64, Ejumula and MUSG0623-09. Vine diameter decreased in Manhissane and MUSG0616-18. No change in leaf length in Tacna and Jonathan and in leaf width in Xihetamakote and Resisto-Nairobi was recorded. The longest petiole length at 30 DAP was recorded by Tacna and the shortest by Nhacutse4. The longest internode length was recorded in 199062.1. Similar to petiole length, Nhacuste4 reported the shortest internode length. The highest number of primary vines was recorded by MUSG0608-61 and lowest by Beauregard. Of the 48 genotypes exposed to water stress, 18 survived until the end of the greenhouse experiment at 60 DAP and were therefore considered to be drought tolerant. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, 2011.

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This study seeks to determine the value of sulfur dioxide as a method for the dehydration of sweet potatoes for use in cow feed.

The Virginian variety and four selections of the Porto Rico variety were planted on two soil types at Toano, and Walkerton, Virginia, and on one soil at Warsaw, Virginia. At Williamsburg, Virginia, the Virginian, Nancy Hall, and a selection of the Porto Rico were planted under aluminum foil mulch, black paper mulch, and on cultivated plots. From these plantings an attempt was made to determine the influence of aluminum foil mulch, black paper mulch, selection or variety, and soil type, on the factors studied. The following summary is given of the results obtained from the “Mulched Treatments” phases of the experiment: 1. Aluminum foil mulch tended to increase the soil moisture and lower the soil temperature as compared to black paper mulch end cultivation. 2. Where the entire plot was covered by unperforated black paper, without some provision for water to reach the soil, the soil moisture is lowered. 3. The carotene content of the Virginian was 3 to 4 times as high as the Porto Rico variety. 4. Neither the yield nor the carotene content of the Porto Rico variety was affected by the aluminum foil, or black paper mulches. 5. The carotene content and yield of the Virginian, and the total yield of the Nancy Hall was higher under aluminum foil mulch than on the cultivated plots. 6. There was no difference between the aluminum foil, black paper, and cultivated treatments in the smoothness and uniformity of shape of the three varieties considered. 7. The Virginian was smoother and more uniform in shape than the Porto Rico or Nancy Hall varieties. The Virginian was also more uniform in skin and flesh color than the Porto Rico variety. The following summary is given of the results obtained from the “Affect of Variety and Selections” and “Affect of Soil Type” phases of the experiment: 1. No variety or selection was consistently higher in yield than all the others. 2. Selection #2 of the Porto Rico variety was the only selection which was consistently among the highest in yield at all locations. 3. The Virginian sweet potato variety was smoother and more uniform in shape than any of the selections of the Porto Rico. 4. No selection of the Porto Rico variety was consistently smoother than the others. Selection #1 was the most consistent selection of the Porto Rico variety to grade high in uniformity of shape. 5. There was no appreciable difference between varieties and selections in their disease susceptibility. 6. No selection or variety was significantly better, in respect to cracking, than the others. 7. The Virginian variety was 3 to 4 times as high in carotene content than any of the selections of the Porto Rico, regardless of location or soil. It was also more uniform in skin and flesh color. 8. None of the selections of Porto Rico was consistently higher in carotene content. Selection #4 varied more than the other selections in the uniformity of skin color. 9. Variety or selection was a more important factor than soil type in determining the yield, carotene content, and uniformity of flesh, and skin color of the sweet potatoes. 10. Soil type did not affect the yield of the Virginian, or selections of Porto Rico at either of the locations. 11. Soil type had only a slight and inconsistent affect on the smoothness, and uniformity of shape of the sweet potatoes. 12. Under the conditions of this experiment there was no consistent difference in soil type in the amount and kind of disease present. / Master of Science

The purpose of the present study is to determine the effect of cooking on the vitamin A value of "Vita-Yam" candy and cookies.

Controlled atmosphere (CA) storage of horticulture crops involves the holding of such produce in refrigerated storage with a reduction of oxygen and an increase in carbon dioxide. The effect of controlled atmospheres on the keeping quality of Centennial, Jersey, Goldrush, Nemagold, Oklamar, and Porto Rico sweetpotato varieties was studied in the 1963-65 period. Evaluations were made of decay loss, weight and dry matter loss, soluble solids percent, carotene content, taste of raw and baked roots, keeping after storage, and the ability of roots to sprout. In 1963-64, ranges of carbon dioxide from 0 to 15 percent were used in combination with 2 to 16 percent oxygen. Sweetpotato roots stored under atmospheres having an oxygen level below 7 percent or a carbon dioxide level above 10 percent developed a high percent of roots with either an alcoholic flavor or an off-flavor. Sweetpotatoes under an atmosphere of 3 percent carbon dioxide and 7 percent oxygen (3-7) had better quality than check lots as evaluated by low total losses due to decay and weight loss, higher dry matter content and a low dry matter loss, high total soluble solids and a high percent of acceptable tasting roots. The only disadvantage of this CA treatment was a higher loss due to decay upon holding at room temperature for one month after storage. However, this high loss was not significantly different from the open air check. In 1964-65 controlled atmosphere levels of 2 to 7 percent carbon dioxide in combination with 7 to 11 percent oxygen were used. Results similar to those of 1963-64 were obtained in 1964-65. Sweetpotatoes under an atmosphere of 2-7 in a gas generated CA room, had better storage quality as measured by low total losses, low dry matter disappearance, higher total soluble solids and a high percent of acceptable tasting roots compared to the checks. Roots removed from CA in 1964-65 and held at room temperature for one month did not exhibit the high decay found in the 1963-64 season. Decay was slightly higher than the check but not significantly different. The 2-7 atmosphere did not impair sprouting when roots were held at a warm temperature after storage. Sweetpotato roots under a 3-8 atmosphere in a sealed 55 gallon drum were relatively similar to roots held in the 2-7 room atmosphere, but were generally poorer in keeping quality. Sweetpotatoes under atmospheres 7-8 and 3-11 had lower total losses compared to the room air or open check, but not the covered drum check. Roots under these controlled atmospheres were not different from the covered check in dry matter loss and were higher in soluble solids, carotene content and percent acceptable tasting roots than the open check. Roots removed from the 7-8 and 3-11 atmospheres had higher decay losses than the checks after holding at room temperature for one month. The 7-8 and 3-11 atmospheres significantly decreased the ability of roots to sprout at room temperature. There were pronounced varietal responses to controlled atmosphere storage. CA holding had a beneficial effect on the Centennial and Jersey varieties and to a lesser degree on the Porto Rico and Goldrush varieties as evaluated by reduction of total losses, dry matter loss, higher soluble solids levels and a higher percent of acceptable tasting roots. More off-flavor developed in roots of the Nemagold and Oklamar varieties. The Nemagold and to a lesser degree the Oklawar had a higher total loss, dry matter loss, and lower soluble solids than the other varieties and after removal from CA and holding at room temperature the Nemagold variety developed more decay. / Ph. D.

The purpose of this present study is to determine the amount of vitamin A in the dehydrated sweet potato made from the yellow Puerto Rico variety grown in Texas by using a reference oil.