Early blight (Alternaria solani Sorauer)is a major foliar disease of potatoes in most growing regions of the world and is underestimated in South Africa. This project studies the epidemiology and control of the disease in South Africa. A decision support system (DSS) for early blight in South Africa was developed and evaluated in field trials. This early blight DSS is the first such system to be developed in South Africa and once incorporated with the late blight model, will represent innovative technology for use in the South African potato industry. Trends in weather variables and concentrations of airborne conidia of A. solani were monitored. Distinct seasonal variation was noted. Peaks in spore concentration coincided with periods favourable for spore formation and dispersal; most notable was diurnal periodicity and interrupted wetting periods. The results obtained from these measurements will be useful in improving early blight DSSs for southern Africa. Isolates of A. solani from various potato-growing regions in South Africa were characterized using virulence, vegetative compatibility (VC) and random amplified microsatellite (RAMS) primers. Neither the virulence assays nor VC tests sufficiently characterised the population. Analysis of RAMS profiles revealed 27% genetic diversity among the isolates. This value is similar to diversity values obtained by previous authors studying A. solani, however, it is relatively high for an asexually reproducing fungus. There was no evidence for geographical clustering of isolates, indicating that isolates are widespread across South Africa. A survey on control practices and grower perceptions of early blight in South Africa was conducted using a questionnaire. These questionnaires were distributed to growers from 10 potato-growing regions in South Africa. Results highlighted the most popular control methods and cultivars in the South African potato industry. The majority of respondents indicated that they would use an accurate, cost-effective early blight DSS, and that more research is necessary on early blight in South Africa. A survey on control practices and grower perceptions of early blight in South Africa was conducted using a questionnaire. These questionnaires were distributed to growers from 10 potato-growing regions in South Africa. Results highlighted the most popular control methods and cultivars in the South African potato industry. The majority of respondents indicated that they would use an accurate, cost-effective early blight DSS, and that more research is necessary on early blight in South Africa. Estimated crop losses ranged from 1% - 60%, with an average of approximately 20%. This is the first comprehensive epidemiological study to be conducted on early blight in South Africa and has highlighted the need for further research. / Thesis (DPhil (Plant Pathology))--University of Pretoria, 2006. / Microbiology and Plant Pathology / unrestricted

The sequence of 3553 nucleotides corresponding to the 3'-terminal region of potato virus S (PVS) has been determined from cloned cDNA. The sequence obtained contains six open reading frames with the potential to encode proteins of Mr 10,734, Mr 32,515, Mr 7,222, Mr 11,802, Mr 25,092 and at least Mr 41,052. The amino acid sequence of the 33K ORF has been confirmed to be that of the viral coat protein gene. The nucleotide sequence of this ORF was obtained from expression plasmids which were isolated by binding with a specific monoclonal antibody to PVS, and the expression of coat protein fusion products was verified by Western blots of bacterial cell lysates. The deduced amino acid sequence of a 70 amino acid portion from the central region of the PVS coat protein was 59% identical to the analogous region of potato virus X. In addition, the 7K, 12K and 25K ORF's displayed significant sequence homology with similar sized ORF's from a number of potexviruses. The partial 41K ORF was homologous with the C-terminal portion of the viral replicase proteins of potato virus X and white clover mosaic virus. While the biological functions of the 12K and 25K non-structural proteins coded for by PVS and members of the potexvirus group remain unknown, the 12K protein displays a hydropathicity profile consistent with a membrane associated protein and the 25K protein contains a conserved sequence motif found in a number of nucleoside triphosphate binding proteins. Members of the carlavirus group are distinguished from the potexviruses by the presence of a small [11K (PVS, potato virus M) - 16K (lily symptomless virus)] 3' terminal ORF which appears to contain a sequence motif similar to the 'zinc-finger' domain found in many nucleic acid binding proteins. The coat protein gene from potato virus S (PVS) was introduced into Nicotiana debneyii tobacco as well as a commercial potato cultivar, 'Russet Burbank', by leaf disc transformation using Agrobacterium tumefaciens. Transgenic plants expressing the viral coat protein were highly resistant to subsequent infection following mechanical inoculation with the Andean or ME strains of PVS as indicated by a lack of accumulation of virus in the upper leaves. The coat protein mediated protection afforded by these transgenic plants was sufficient to prevent the accumulation of virus in the tissues of non-transformed 'Russet Burbank' shoots which had been grafted onto transgenic plants inoculated with PVS, and in reciprocal grafts, transgenic shoots accumulated less than 2% (6 weeks after grafting) of the concentration of PVS found in non-transformed shoots similarly grafted onto plants systemically infected with PVS. These transgenic plants also displayed a measure of resistance to inoculation with a related carlavirus from potato, potato virus M. In agreement with previous reports for plants expressing PVX coat protein, plants expressing PVS coat protein were also protected from inoculation with PVS RNA. These results provide further evidence that coat protein mediated protection for these two groups of viruses, which share similar genome organizations, may involve inhibition of some early event in infection, other than, or in addition to, virus uncoating. Specific monoclonal antibodies were prepared against a C-terminal derived 18 kDa portion of the 25K protein of PVS expressed as an in-frame chimeric fusion protein with the glutathione S-transferase gene. The in vivo expression of this non-structural protein in virus infected tissue, as well as tissue from transgenic tobacco (var Xanthi-nc) engineered to contain the entire 25K gene, was verified by Western immunoblot labelling. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate

The effect of cytokinin and gibberellin, and in particular a combination of the two, on termination of dormant potato tubers was investigated. The objective was to effectively terminate dormancy through the external application of a combination of cytokinin and gibberellin. Freshly harvested tubers were treated and either cut at the stolon end with the apical portions placed on moist cotton wool, or left intact and dry. Tuber segments treated with a high concentration of cytokinin (0.1g.Lˉ¹) or a combination of cytokinin and gibberellin sprouted within 5 days, whereas high gibberellin concentrations (0.1g.Lˉ¹) stimulated sprouting within 9 days. Untreated tuber segments supplied only with moisture terminated dormancy later than hormonal treated tubers, but much earlier than segments that were kept dry. Tuber segments treated with a combination of cytokinin and gibberellin, or a high concentration of gibberellin (0.1g.Lˉ¹), produced more and longer sprouts than tubers treated with only cytokinin (0.1g.Lˉ¹) or a low concentration of gibberellin (0.005g.Lˉ¹). Sprouts on tuber segments treated with a combination of cytokinin and gibberellin attained maximum sprout growth rate nine days after treatment, but thereafter the growth rate decreased. This decrease may be a consequence of closed plasmodesmata although membrane permeability and its affect on assimilate availability may play a role. This phenomenon deserves further research attention. Removal of wound periderm did not reactivate sprout growth. The wounding of tubers by removing a portion at the stolon end and supplying moisture greatly enhanced the termination of dormancy and subsequent sprout growth, indicating that the availability of water may be a factor in initiation of sprouts. The results are compatible with the hypothesis that cells in dormant buds are arrested in the G1 phase of the cell cycle. Cytokinin is needed to initiate cell cycling, but gibberellin is also needed to initiate and maintain cell growth. These two growth regulators are also involved in the opening of the plasmodesmata as well as the creation of new plasmodesmata witch would establish communication between the apical meristem and the rest of the tuber. / Dissertation (MSc(Agric))--University of Pretoria, 2008. / Plant Production and Soil Science / unrestricted

Submitted by Reginaldo Soares de Freitas (reginaldo.freitas@ufv.br) on 2015-11-16T08:19:22Z No. of bitstreams: 1 texto completo.pdf: 903972 bytes, checksum: 718ef28c619da309d55908637b1418a5 (MD5) / Made available in DSpace on 2015-11-16T08:19:23Z (GMT). No. of bitstreams: 1 texto completo.pdf: 903972 bytes, checksum: 718ef28c619da309d55908637b1418a5 (MD5) Previous issue date: 2013-12-17 / O sistema Viçosa de cultivo do tomateiro foi proposto e teve a eficiência econômica e agronômica comparadas às dos sistemas Vertical e Cerca Cruzada. Obtendo produtividades superiores e economia de insumos em relação aos outros sistemas. Porém, os estudos realizados não esclareceram as razões que levaram o sistema Viçosa a ser mais sustentável que os demais. Neste trabalho, procurou-se avaliar o comportamento dos parâmetros de crescimento, produtivos, de trocas gasosas e emissão de fluorescência da clorofila a para elucidar os ganhos produtivos alcançados no sistema Viçosa de cultivo do tomateiro em relação aos sistemas Vertical e Cerca Cruzada. Sendo assim, dois experimentos foram conduzidos no ano de 2012 em Viçosa, MG. Os incrementos em produtividade obtidos no sistema Viçosa, com maior número de plantas por área, em relação aos demais sistemas, foram acompanhados de aumentos na taxa fotossintética líquida e manutenção da taxa transpiratória e da temperatura foliar. A produção total de frutos por planta não foi influenciada pelos sistemas de cultivo. No tomateiro cultivado no sistema Viçosa foi observado crescimento tardio em relação aos demais. Estudos adicionais ainda são necessários para se compreender o comportamento produtivo do tomateiro conduzido no sistema Viçosa. / Viçosa tomato growing system, recently proposed, had the economic and agronomic efficiency compared to the Vertical and Cerca Cruzada tomato systems. Getting higher yields and more sustainable than other systems. However, those studies have not clarified the reasons for the Viçosa system to be more productive and economical than Vertical and Cerca Cruzada system. In this study, we aimed evaluate the behavior of the growth, production, gas exchange and emission of fluorescence from chlorophyll a for elucidate the sustainability gains achieved at the Viçosa system tomato cultivation, with more plant per area, regarding to Vertical and Cerca Cruzada systems. Thus, two experiments were conducted in 2012 in Viçosa, MG. The productivity increasing achieved in Viçosa system were accompanied by increasing in net photosynthetic rate and maintenance at transpiration rate and leaf temperature. The total fruit yield per plant was not affected by cropping systems. The tomato conducted in Viçosa system showed late growth compared to Vertical and Cerca Cruzada systems. Additional studies are required to understand the behavior of tomato conducted in Viçosa system.

Submitted by Marco Antônio de Ramos Chagas (mchagas@ufv.br) on 2018-09-26T18:26:26Z No. of bitstreams: 1 texto completo.pdf: 2755378 bytes, checksum: 5ebfe5d8ce064b9ec4f37f421ff91315 (MD5) / Made available in DSpace on 2018-09-26T18:26:26Z (GMT). No. of bitstreams: 1 texto completo.pdf: 2755378 bytes, checksum: 5ebfe5d8ce064b9ec4f37f421ff91315 (MD5) Previous issue date: 2018-02-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo deste estudo foi verificar o efeito da temperatura, tempo de armazenamento e dano mecânico nos tubérculos destinados ao processamento de batata pré-frita. Foram realizados dois ensaios. No primeiro, a cultivar Markies foi armazenada em câmara climatizada a 4, 5, 6 e 8 oC (UR ± 90%) por 240 dias, com quantificação do teor de açúcar solúvel total (AST), açúcares redutores (AR), atividade das enzimas peroxidase (POD) e polifenoloxidase (PPO), coloração após a fritura, e incidência da brotação. No segundo ensaio, tubérculos das cultivares Markies e Challenger foram submetidos a danos mecânicos e armazenados em câmaras climatizadas nas temperaturas de 8, 14 e 20 °C (UR ± 90%) por 14 dias para determinação do período de formação da periderme de dano. Após este período, avaliou-se taxas de perda de massa fresca, teor de açúcar solúvel total (AST), açúcares redutores (AR), açúcares não redutores (ANR), coloração dos palitos após a fritura e a taxa de regeneração da periderme após o dano. A cultivar Markies a 6,9 oC, apresentou menores concentrações de AST e AR nos tubérculos aos 78,4 e 92,9 dias de armazenamento, respectivamente. A atividade das enzimas POD e PPO não foram influenciadas pelas temperaturas de 4, 5, 6 e 8 oC, nem pelo tempo de armazenamento de 240 dias apresentando valor médio de 1,91 e 1,42 UA min -1 mg -1 de proteína, respectivamente. Houve variação na coloração dos tubérculos após a fritura, com coloração mais escura nos tubérculos armazenados a 4 e 5 °C, os tubérculos armazenados a 6 e 8 °C mantiveram a coloração dento do padrão aceitável até os 240 dias de armazenamento. As temperaturas de 4 e 5 °C retardaram o início da brotação, iniciando-se aos 150 dias. A 6 e 8°C o início da brotação se deu a partir dos 90 e 60 dias de armazenamento, respectivamente. Para a cura, nas temperaturas avaliadas de 8, 14 e 20 oC, verificou-se taxa de perda de matéria fresca superior nos tubérculos que sofreram danos, sendo que a 14 oC a taxa de perda de ambas cultivares apresentaram comportamento quadrático com taxa de perda mínima nos tubérculos com dano para a cultivar Markies aos 10,8 dias e para a cultivar Challenger em 10,46 dias. Os maiores teores de AST, AR e ANR ocorreram a 8 °C tanto para os tubérculos do controle quanto para os tubérculos submetidos a danos na cultivar Markies, e apenas nos tubérculos com danos para a cultivar Challenger. Entre as cultivares Markies e Challenger verificou-se valores médios de AST, AR e ANR superiores para a cultivar Markies a 8 °C. É possível armazenar a cultivar Markies por 92,9 dias a 6,9 °C sem perda de qualidade para processamento industrial. Além disso, verificou-se que a cura das cultivares Markies e Challenger a 8, 14 e 20 oC causaram modificações anatômicas conspícuas nos tubérculos com dano, sendo que 14 oC foi a temperatura que proporcionou melhor cura. / The objective of this study was to verify the effect of temperature, lenght of storage and mechanical damage on the tubers intended for processing as French fries. Two assays were done. In the first experiment, the cultivar Markies was stored in an air-conditioned room at 4, 5, 6 and 8 oC (RH ± 90 %) for 240 days. Total soluble sugar (AST), reducing sugars (AR) and non-reducing sugars (ANR) levels, peroxidase (POD) and polyphenoloxidase (PPO) enzymes activity, browning after frying, and sprouting incidence were evaluated. In the second experiment, tubers of the cultivars Markies and Challenger were subjected to mechanical damage and stored at 8, 14 and 20 °C (RH ± 90 %) for 14 days to determine the period of formation of the damage peridem. Loss rate of fresh mass, total soluble sugar content (AST), reducing sugars (AR), non-reducing sugars (ANR), French fries color after frying and regeneration rate of the periderm after wounding were evaluated. Markies cultivar stored at 6.9 oC presented the lowest AST and AR concentrations in the tubers at 78.4 and 92.9 days of storage, respectively. POD and PPO enzymes activity were not influenced by temperature (4, 5, 6 and 8 oC), nor by storage period (240 days) presenting average values of 1.91 and 1.42 AU min -1 mg -1 protein, respectively. There was variation in tuber coloration after frying, with darker color in tubers stored at 4 and 5 oC, while those stored at 6 and 8 oC maintained acceptable coloration standard up to 240 storage days. Temperatures of 4 and 5 °C delayed the sprouting onset, starting at 150 days. At 6 and 8 °C the sprouting onset occurred at 90 and 60 days of storage, respectively. For wound healing, at the temperatures of 8, 14 and 20 oC, it was verified higher loss rate of fresh matter in tubers that suffered damages. At 14 oC loss rate of both cultivars presented quadratic behavior with minimum loss rate in tubers that suffered mechanical wounding for Markies cultivar at 10.8 days and in Challenger cultivar at 10.46 days. The highest levels of AST, AR and ANR occurred at 8 °C for both the control tubers and the tubers that suffered wounding for Markies cultivar, and only in the tubers that suffered for cultivar Challenger. Comparing the cultivars Markies and Challenger, the levels of AST, AR and ANR were higher in Markies cultivar at 8 °C. Based on the results, it is possible to store cultivar Markies cultivar for 92.9 days at 6.9 °C without quality loss for industrial processing. Healing of Markies and Challenger cultivars at 8, 14 and 20 ° C caused conspicuous anatomical modifications in the wounded tubers being the best temperature for healing at 14 °C.

O objetivo do estudo foi avaliar o efeito da utilização de película de metilcelulose e das atmosferas de acondicionamento com ar atmosférico, vácuo e argônio sobre a conservação de batatas minimamente processadas (MP) e também sobre sua qualidade após fritura. Tubérculos foram selecionados, lavados, sanificados, cortados na forma de palitos e tratados com ácido cítrico. As batatas foram imersas em solução filmogênica contendo metilcelulose (1%) e sorbitol (0,75%) como plastificante, com posterior secagem, acondicionadas sob ar atmosférico, e modificada com argônio (20seg. e 230mmHg), além de vácuo (15seg. e 54mmHg). O produto MP armazenado a 8°C durante 12 dias foi avaliado em intervalos de 3 dias mediante análises microbiológicas, fisiológicas, físicoquímicas e físicas. A cada 3 dias as batatas MP foram também fritas e avaliadas quanto à perda de umidade, absorção de óleo, textura instrumental e avaliação sensorial. O acondicionamento sob ar atmosférico foi efetivo em reduzir a perda de massa das batatas MP. As embalagens sob vácuo foram mais efetivas para o produto MP sem película, pois mantiveram o pH, acidez titulável, teor de amido e de açúcares mais próximos do dia do início do experimento, como também mantiveram baixo o índice de escurecimento. O acondicionamento sob vácuo, entretanto, não seria indicado quando a finalidade fosse a fritura, pois foi o tratamento que apresentou maiores perdas de umidade e maior absorção de óleo. O acondicionamento sob atmosfera de argônio também foi mais efetivo nas batatas MP sem película, sendo fator determinante em reduzir os teores de CO2 no interior da embalagem, apresentou menor taxa respiratória, menor índice de escurecimento tanto antes como após a fritura, reduziu a perda de umidade durante a fritura, manteve mais a firmeza do produto frito e também minimizou a absorção de óleo a partir do 3° dia de armazename nto. A utilização de película foi efetiva em reduzir a respiração do produto MP até o 6° dia. Já no produto frito, foi fator determinante na retenção de umidade das batatas, como também na redução, ao longo do armazenamento, da absorção de óleo / The aim of this study was to evaluate the effect of methylcellulose as edible coating and packaging atmospheres with atmospheric air, vacuum and argon on the conservation of minimally processed (MP) potatoes as well as on their quality after frying. Tubers were selected, washed, sanitized, cut in the shape of sticks and treated with citric acid. Potatoes were immersed in a filmogenic solution of methylcellulose (1%) with sorbitol (0,75%) as a plasticizer, dehydrated, and then packaged under atmospheric air, and modified with argon (20seg. e 230mmHg), and vacuum (15seg. e 54mmHg). Stored MP product at 8°C for 12 days was assessed at intervals of 3 days by microbiological, physiological, physicochemical and physical analyses. Every 3 days the MP potatoes were fried and evaluated for moisture loss, oil absorption, instrumental texture and sensory evaluation. Packaging under atmospheric air was effective in reducing the mass loss of MP potatoes. The vacuum packaging was more effective for the MP product without edible coating, because they kept the pH, acidity, starch and sugar level more similar to the first day experiment, as well as low browning rate. The vacuum packaging, however, would not be appropriate when the purpose is frying, because this treatment showed the greatest loss of moisture and increased oil absorption. Packaging under argon atmosphere was also more effective for the MP product without edible coating, and it was an important factor to reduce CO2 levels inside the package, showed lower respiratory rate, lower browning index both before and after frying, reduced moisture loss during frying, kept fried product firmness better and also minimized oil absorption from the 3rd day of storage. The use of edible coating was effective in reducing the respiration of MP product until the 6rd day. For the fried product, the use of coating was a determining factor for moisture retention during frying of potatoes, and also to decrease oil absorption along the potato storage.

Thesis (M. Sc. Agric.(Plant Production)) -- University of Limpopo, 2019 / Nightshade (Solanum retroflexum Dun.) is among the most important indigenous leafy vegetables in Vhembe District, Limpopo Province, South Africa, due to its high values of beta-carotene, vitamin E, folic acid, ascorbic acid, calcium, iron and protein. Vhembe District occurs in the tropical regions of Limpopo Province and the production of vegetables is dependent upon the availability of irrigation water. An Integrated Drip Irrigation System (IDIS) and a 3S planter were developed to save water by planting several plants/hole of drip irrigation system. The subsystems in IDIS allow for the production of different crops with different water requirements, whereas the 3S planter can be used for planting from one to nine plants/hole of drip irrigation system. Also, the subsystems could be used in assessing irrigation interval for crops under various planting densities. The interaction of irrigation interval and planting density of S. retroflexum had not been documented. The objective of this study, therefore, was to determine the interactive effects of irrigation interval and planting density on biomass yield and chemical nutrient elements (summer harvest only) of S. retroflexum under field conditions. The irrigation interval and planting density/hole were arranged in a split-plot experimental design, with eight replications. The main plot was irrigation interval and the subplot was the planting densities. Harvesting was done twice for both summer and winter experiments. The first harvest (H1) was done at 6 weeks after transplanting, with the second harvest (H2) being done at six weeks after the first harvest. Fresh shoots were oven-dried at 60°C for 72 h for the determination of dry matter. Mature leaves were powdered and analysed for mineral content (Ca, P, K, Mg, Na, Fe, Zn, Mn and Cu) using the ICPE-9000. Data were subjected to analysis of variance using SAS software. In the summer experiment, the interaction was significant (P ≤ 0.05) for dry shoot mass at H1 and H2. However, the contribution of xv the interaction in the total treatment variation (TTV) of the variable was negligent and therefore, only single factors were reported. Irrigation interval and planting density had highly significant (P ≤ 0.01) effects on plant variables during H1 and H2 in summer and winter. However, irrigation interval effects for dry shoot mass were not significant for summer H2. Interaction effects were significant for Ca, P, K, Mg, Mn and Cu in leaf tissues during summer H1, but were not significant for Na, Fe and Zn. Also, irrigation interval was significant for Ca, Mg, P, K, Na, Fe, Zn, Mn and Cu during summer H1, whereas planting density had no significant effects for all chemical nutrients except for Ca, P and K during summer H1. Dry shoot mass of S. retroflexum increased linearly with increasing irrigation interval and planting density. Results suggested that most nutrient elements increased with deficit irrigation water and higher planting density, whilst P decreased under high planting density. The study showed that there is a high potential for saving water through longer irrigation intervals and produce good high yields at a higher planting density. In conclusion, the use of IDIS and 3S planter to promote growth and accumulation of essential nutrient elements on S. retroflexum demonstrated that longer irrigation interval and higher plant density per drip irrigation hole could be suitable for cultivation of this indigenous vegetable. The recommendation of this study is that higher planting density and longer irrigation intervals are key determinants of higher biomass yield and water saving strategies for large-scale production of the crop. Further, the mineral composition of the crop was under the influence of higher planting density and irrigation intervals.

Thesis (M. A. Agriculture (Plant Protection)) -- University of Limpopo, 2019 / The successful cultivation of nightshade (Solanum retroflexum) as a leafy vegetable with the nutritional potential of contributing to food security in marginalised communities of Limpopo Province could be limited by high population densities of root-knot (Meloidogyne species) nematodes. However, the use of Nemarioc-AL/AG and Nemafric-BL/BG phytonematicides in suppressing nematodes and not being phytotoxic requires the empirically-developed non-phytotoxic concentration, technically referred to as Mean Concentration Stimulation Point (MCSP). The MCSP, developed using the Curve-fitting Allelochemical Response Data (CARD) computer-based model, is crop-specific, hence it should be developed for every crop. The objective of this study was to investigate the influence of Nemarioc-AL/AG and Nemafric-BL/BG phytonematicides on growth of nightshade, accumulation of essential nutrient elements and cucurbitacin residues in nightshade leaves. Microplots were established by inserting 20-cm-diameter plastic pots into 10-cm-deep holes at 0.6 m intra-row and 0.6 m inter-row spacing. Each pot was filled with 10 000 cm3 steam-pasteurised river sand and Hygromix at 3:1. After establishment, Nemarioc-AL and Nemafric-BL phytonematicides were applied at 7-day interval, whereas, Nemarioc-AG and Nemafric-BG phytonematicides were only applied at planting. Two separate experiments for Nemarioc-AL and Nemafric-BL phytonematicides were conducted in summer (November-January) 2017/2018 under microplot conditions with each comprising treatments namely; 0, 2, 4, 8, 16, 32 and 64%, similarly, two separate experiments for the following phytonematicides, Nemarioc-AG and Nemafric-BG comprised treatments namely; 0, 2, 4, 6, 8, 10 and 12 g arranged in a randomised complete block design (RCBD), with 12 replications. The nutrient elements in leaf tissues of nightshade were analysed using the inductively coupled plasma optical emission spectrometry (ICPE-9000) while, cucurbitacin A and B were xii each quantified using the isocratic elution Shimadzu HPLC Prominence with Shimadzu CTO-20A diode array detector. Plant growth and nutrient elements variables were subjected to the CARD computer-based model to generate biological indices to generate the curves, quadratic equations and the related biological indices (Dm, Rh, k) (Liu et al., 2003). The MCSP values were calculated using the biological indices of plant or nutrient element variables which, along with increasing concentration of Nemarioc-AL, Nemafric BL, Nemarioc-AG and Nemafric-BG phytonematicides, exhibited positive quadratic relations, with R2 ≥ 25. Using cucurbitacin A and B standards, residues of Nemarioc AL/AG and Nemafric-BL/BG phytonematicides, were not detected in nightshade leaves, respectively. Dry root mass and dry shoot mass of nightshade over increasing concentration of Nemarioc-AL phytonematicide each exhibited a quadratic relationship, with the models explained by 93 and 61%, respectively. Dry root mass, dry shoot mass, plant height, chlorophyll content and stem diameter against increasing concentration of Nemafric-BL phytonematicide each exhibited positive quadratic relationships with the models explained by 95, 72, 65, 78 and 62%, respectively. Plant height, stem diameter and dry root mass against increasing concentration of Nemarioc-AG phytonematicide each exhibited positive quadratic relationships with their models explained by 93, 88 and 91%, respectively. Dry shoot mass and stem diameter against increasing concentration of Nemafric-BG phytonematicide each exhibited positive quadratic relationships with their models explained by 94 and 84%, respectively. Na, Fe and K over increasing concentration of Nemarioc-AL phytonematicide each exhibited positive quadratic relationships with their associations explained by 96, 91 and 95%, respectively. Zn over increasing concentration of Nemafric-BL phytonematicide exhibited positive quadratic relationship with the model explained by 98%. Fe over increasing concentration of Nemarioc-AG phytonematicide exhibited positive quadratic xiii relationship with the association explained by 91%. Fe, Na, K and Zn over increasing concentration of Nemafric-BG phytonematicide each exhibited positive quadratic relationships with their associations explained by 81, 90, 80 and 89%, respectively, whereas, on the contrary, Zn over increasing concentration of Nemarioc-AG phytonematicide exhibited negative quadratic relationship with the association explained by 96%. Significant (P ≤ 0.05) plant variables were subjected to CARD, to generate biological indices which were used to compute the MCSP using the relation: MCSP = Dm + Rh/2 and the overall sensitivity value (∑k). In Nemarioc-AL phytonematicide trial, MCSP = 3.02% and ∑k = 1 for plant variables, whereas, MCSP and ∑k for nutrient elements were 12.09% and 1, respectively. In Nemafric-BL phytonematicide trial, MCSP = 3.08% and ∑k = 0 for plant variables, while MCSP = 2484.14% and ∑k = 0 for nutrient elements. In Nemarioc-AG phytonematicide trial, MCSP = 3.47 g and ∑k = 0 for plant variables, whereas, for nutrient elements MCSP = 8.49 g and ∑k = 1. In Nemafric-BG phytonematicide trial, MCSP = 4.70 g and ∑k = 0 for plant variables, whereas, MCSP =723.75 g and ∑k = 1 for nutrient elements. In conclusion, the application of Nemarioc-AL/AG and Nemafric-BL/BG phytonematicides had the ability to stimulate the growth of nightshade and enhance the accumulation of the selected nutrient elements without leaving cucurbitacin chemical residues in leaf tissues of nightshade. / National Research Foundation (NRF) and the Land Bank Chair of Agriculture

Orientador: Rogério Falleiros Carvalho / Resumo: O nitrogênio (N), elemento essencial ao crescimento e desenvolvimento vegetal, é absorvido principalmente como nitrato (NO3-). Esse elemento pode controlar a arquitetura de raízes e dessa forma favorecer a absorção de nutrientes pelas plantas. Para isso, tem sido mostrado que esses eventos estão relacionados ao controle hormonal, especialmente as auxinas, pois esse hormônio controla o crescimento das raízes de modo dependente de NO3-. Entretanto, esses mecanismos são complexos, pois dependem de várias moléculas, especialmente peróxido de hidrogênio (H2O2), o qual parece atuar nas sinalizações das auxinas em situações estressoras nas plantas, a exemplo da deficiência de N. Entretanto, a forma como auxinas e H2O2 interagem nas raízes sob deficiência de N foi pouco explorado. Assim, objetivou-se verificar se as auxinas dependem de H2O2 nas respostas das raízes de tomateiro à deficiência de NO3-. Para isso, plantas de da cultivar Micro-Tom de tomateiro foram cultivadas em hidroponia sob suficiência e deficiência de NO3-, ambas com presença e ou ausência de inibidor de transporte de auxinas, o (ácido 2,3,5-triiodo-benzóico- TIBA) e inibidor do acúmulo de H2O2 (Catalase). O delineamento experimental foi inteiramente casualizado, disposto em fatorial 2x4, com três repetições. Foi analisado comprimento e biomassa seca da parte aérea e biomassa seca, comprimento, área e volume das raízes. Além disso, foi quantificado conteúdo de MDA e H2O2. A deficiência de NO3- diminuiu o crescimento... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Nitrogen (N) is essential for plant growth and development, and is mainly absorbed as nitrate (NO3-). It also controls root architecture, improving plant nutritional status. These characteristics are related to hormonal control, especially by auxins. Auxins control root growth via NO3-dependent cell expansion, but these mechanisms are complex and depend on several molecules. Hydrogen peroxide (H2O2) appears to act on these auxins signalling in plant stress situations. However, how auxins and H2O2 interact in roots under N deficiency has not been well explored. Therefore, this study aimed to verify if auxins depend on H2O2 for responses of tomato roots to N deficiency. Micro-Tom plants were grown in hydroponic systems under sufficiency and deficiency of NO3-, both with and without auxin transport inhibitor, 2,3,5-triiodo-benzoic acid (TIBA), and the inhibitor of H2O2 accumulation (Catalase) in plants. The experiment was carried out in a completely randomized design in a factorial scheme (2x4) with three replications. Shoot length and dry biomass, as well as root dry biomass, length, area and volume were analysed. In addition, MDA and H2O2 content were also quantified. NO3- deficiency reduced shoot growth and, interestingly, promoted higher root growth. Furthermore, TIBA inhibited root growth under both NO3- conditions and the presence of catalase in NO3-deficiency resulted in lower root growth. These results show that auxins depend on H2O2 for tomato root responses to N defici... (Complete abstract click electronic access below) / Mestre

Meloiodgyne incognita, one of the most aggressive plant parasitic nematodes species on potato in South Africa, belongs to a group of plant parasitic nematodes commonly known as root knot nematodes (RKN). This group of nematodes is widely distributed throughout the world. Meloidogyne spp. cause major economic losses to important crops such as potato and therefore decrease their market value in many countries across the world. The second stage juveniles are the only mobile and infective phase of the root knot nematode. As they infect host roots, they create wounds that can be used by other plant pathogens to penetrate the host in large numbers. The most effective management strategy for root knot nematodes is the use of nematicides such as Temik and Methyl bromide. However, these have been banned due to adverse on the environment. Therefore, Meloidogyne spp. will inevitably become a big problem in the potato industry of many countries due to the lack of effective alternatives to banned chemicals. Pectobacterium carotovorum subsp. brasiliensis (Pcb) is one of the most important soft rot-causing agents in South Africa. This pathogen belongs to a group of pathogens commonly known as soft rot Enterobacteriaceae (SRE). Bacteria belonging to this group of pathogens are known to cause soft rot and blackleg diseases on potato and other crops. Pcb is known as an opportunistic pathogen that can only penetrate host root tissue through natural openings or wounds that result from a variety of agents. Post penetration, the bacteria will increase in number and cause soft rot and blackleg. As rotting plant tissue disintegrates the bacteria escapes into the soil where it serves as inoculum and can infect healthy hosts. Many interactions have been documented between Meloidogyne spp. and other plant pathogens but to our knowledge there are no interactions that have been reported between Meloidogyne spp. and Pectobacterium spp. Considering the life cycles of RKN and SRE, we hypothesised that there could be an interaction between the two pathogen groups. Since both RKN and SRE are potato pathogens, they share the same space in the rhizosphere. This likely can lead to synergies and complex formation between the two pathogens. Likely, the wounds created by RKN J2s as they penetrate plant tissue can potentially be used by opportunistic Pcb to infect various hosts. It is from these identified overlaps that the first part of this study focused on investigating the potential interaction between M. incognita and Pcb. The first objective was to determine whether Pcb can attach onto M. incognita J2s and, if this was the case, to determine whether the J2s can disseminate the bacteria as they move around in the environment. The second objective was to determine whether there is a synergistic interaction between RKN and SRE and the combined effect of the two pathogens on their host Solanum tuberosum cv Mondial. The results obtained in the first part of the study strongly suggested that Pcb can attach onto M. incognita J2s and can be disseminated as the J2s move around in the environment. Thus, this indicated that there is a synergistic interaction between M. incognita and Pcb as there was increased disease severity and incidence in plants inoculated with both pathogens compared to those inoculated with individual pathogens. Significantly higher Pcb concentrations were found in plants inoculated with both pathogens. There was no breakage of tolerance to Pcb-caused blackleg on an otherwise resistant cultivar, BP1. The second aim of this study was to determine whether the induction of natural resistance using environmentally friendly resistance inducing chemicals can potentially be used as an alternative to chemical control. To this end, the effect of three inducers at different concentrations, amongst DL-β-aminobutyric acid, Acibenzolar-s-methyl and Messenger on potato plants infected with RKN was compared. The most effective resistance inducer amongst the three was 20mM BABA as it was able to reduce the number of J2s that penetrated host tissue, the number of females in the roots and the rate of egg production. Furthermore, the galling index observed in potato roots was significantly lower when plants were treated with 20mM BABA. Additionally, the reduced rate of RKN infection in plants primed with 20mM led to a decrease in the rate of Pcb infection. / Dissertation (MSc)--University of Pretoria, 2013. / gm2013 / Microbiology and Plant Pathology / Unrestricted