No abstract available. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1999.

Thesis (M.Sc. Agriculture (Agronomy) -- University of Limpopo, 2019 / Erratic rainfall and insect infestation are some of the factors that limit cowpea production in Limpopo (Asiwe, 2009). Improved cowpea varieties available for dryland production in Limpopo do not meet the farmer’s needs. Specific trait crosses are needed to be made with adapted varieties for the purpose of developing high yielding, pest tolerant and adapted varieties. Varieties with desired specific traits were planted in isolation plots for outcrossing by insects. F1 lines derived from parental lines that were half sib seeds were harvested and planted as F2, and seeds obtained from F2 generation were used to develop F3 segregating population at University of Limpopo Experiential Farm, Syferkuil, and planted along with parents. This F3 generation forms the current evaluation on which this report is based. Data collected included; aphid severity (measured on a 9-point scale), number of days to 90 % maturity, grain yield, 100 seed weight and number of genotypes selected for advancement. Results showed significant variation among progeny over parents therefore expressing transgressive segregation. Genotypes derived from pedigree TX08-30-5 were five while pedigree IT98K-205-8 and IT97K-499-35 had four genotypes each that expressed early maturity (80-90 days) which are desirable for evading drought. Twenty-three genotypes from pedigree GEC and three from pedigree IT97K-499-35 obtained grain yield (>101 g/plot and >161 g/plot) that was better than their parents. Only one genotype derived from pedigree TX08-30-1 expressed high resistance to aphids better than the parent with a mean aphid score range of 1-2. Four genotypes from pedigree TX08-30-5 obtained bigger 100 seed weight (>18.6 g) compared to parent. These progeny also proved to be high yielders as they expressed heterosis for all yield attributes than their parents. Eighty-two genotypes were selected for advancement. Significant variations were observed among progeny giving opportunity to make selections. In most cases, genotypes outperformed their parents which indicate positive heterosis. The 82 promising genotypes selected will be advanced for further selections from multi location testing for stability and adaptation.

The land reform that has unfolded in Zimbabwe since 1980 used different models and had diverse consequences. Since the implementation of the fast tract land reform programme in 2000, Zimbabwe experienced heavy reduction in yield and output at farm level that led to a 70% shortfall in production to meet annual food requirements (Richardson, 2005). The economic crisis in Zimbabwe has been characterized by worsening food insecurity especially in the rural areas where harvests continue to be poor. In the beef sector, Zimbabwe has failed to meet its export quota to the EU. The shortfall in production to meet annual food requirements shows a very grim situation but do not tell us about the performance of resettled farmers who now occupy much of the productive land. The broad objective of the study was to determine and compare the production efficiency of resettled farmers in Zimbabwe across land reform models. In addition, the study determined land use intensity. The study was conducted in the Mashonaland Central Province of Zimbabwe mainly because a wide variety of field crops were grown by resettled farmers. The respondents were stratified into three groups. These were: beneficiaries of land reform before 2000 (resettle scheme), fast track A1 model and fast track A2 model. The three models differ on how they were implemented and supported and this might result in different efficiencies of the models. A total of 245 copies structured questionnaire were administered on the resettled farmers from June to September 2010. Descriptive statistics was applied to the basic characteristics of the sampled households. The effect of model of land reform, gender of the household head, marital status, age of the household head, education, household size, religion, dependence ratio, whether the farmer was fulltime or part-time in farming, experience of the farmers in farming at that environment, total land size owned by the farmers and soil type on revenue per hectare and land use rate were determined using the GLM procedure of SAS (2003). Significance differences between least-square group means were compared using the PDIFF test of SAS (2003). The relationship between Revenue and land utilization was examined using the Pearson‟s correlations analysis. Dependance between response variables that had an effect on either revenue per hectare or land utilization with all the other response variables was tested using the Chi-square test for dependance. To find the effect of arable land used and herd size on revenue per hectare and land use the RSREG Procedure of SAS (2003) was used. Input oriented DEA model under the assumption of constant return to scale was used to estimate efficiency in this study. To identify factors that influence efficiency, a Tobit model censored at zero was selected. The mean land use rate varied significantly (p<0.05) with the land reform model with A2 having highest land use rate of 67%. The A1 and old resettlement households had land use rates of 53% and 46%, respectively. Sex, marital status, age of the household head, education and household size significantly affected land use (P<0.05). Revenue per hectare was not affected by any the factors that were inputted in the model. Results from the DEA approach showed that A2 farmers (large land owners) had an average technical efficiency score of 0.839, while the lowest ranking model (A1) had an average score of 0.618. Small land holders (A1 and the old resettled farmers) are on average less cost-efficient than large land owners, with a score of 0.29 for the former compared with 0.45 for the latter. From the factors that were entered in the Tobit model, age of household head, excellent production knowledge and farmer status affected technical efficiency whereas allocative efficiency was only affected by good production knowledge, farm size, arable land owned and area under cultivation. Factors which affected economic efficiency of the resettled farmers are secondary education, household size, farm size, cultivated area and arable land owned. None of the included socio-economic variables has significant effects on the allocative and economic efficiency of the resettled farmers. Thus, the allocative and economic inefficiencies of the farmers might be accounted for by other natural and environmental factors which were not captured in the model.

<p dir="ltr">Bacterial Wilt, caused by <i>Ralstonia solanacearum</i>, is among the most devastating plant diseases in the world. This pathogen causes significant loss in crops such as tobacco, potato, and tomato. <i>R. solanacearum</i> root infection and xylem colonization determine disease outcome. To date, little is known about the defense mechanism mediated by roots to prevent <i>R. solanacearum</i> vascular colonization during the initial infection stages. Plant early responses are important since they may impact disease outcomes<i>.</i><i> </i>Here, we report the formation of root hairs and primary root growth inhibition in tomato seedlings as <i>Ralstonia</i>-induced phenotypes that depend on tomato genotype and <i>Ralstonia</i> species. The <i>Ralstonia</i>-induced root phenotypes are independent of a functional type III secretion system and exopolysaccharide production (EPS). We also found that <i>R. solanacearum</i><i> </i>K60 infection increased auxin levels throughout the root meristem in wilt-susceptible tomato roots. Our data suggest proper auxin signaling and transport are important for susceptibility to <i>R. solanacearum</i> K60. Blocking auxin transport pharmacologically or genetically led to fewer wilting symptoms, suggesting that auxin is important during early infection stages and disease outcomes in tomato. We previously found that a tomato mutant defective in auxin transport and signaling, known as <i>diageotropica</i> (<i>dgt</i>), has enhanced resistance to <i>R. solanacearum</i> K60. We characterized the resistant response in the <i>dgt</i> mutant, and we found that the resistant response in the <i>dgt</i> mutant may be due to increased lignin content preventing pathogen vasculature colonization. <i>DGT</i> encodes a cyclophilin protein that regulates auxin transport and signaling. Mutations in the cyclophilin DGT promote resistance to <i>R. solanacearum</i> K60. DGT has been reported to regulate auxin transport and signaling. However, the molecular mechanism regarding how DGT mediates these processes is still unknown. We used Yeast Two-Hybrid to identify candidate protein interactors, and we found that SlbZIP1/SlbZIP29, Sl14-3-3, and SlMYB110 may interact with DGT to regulate both development and defense responses. Understanding the role of DGT, auxin, and lignin in defense responses to <i>R. solanacearum</i> K60 in tomato is necessary for Solanaceae crop improvement.</p>

The two-spotted spider mite (TSM), Tetranychus urticae Koch, is an important pest of many greenhouse and field crops worldwide. The development of resistance in TSM populations to chemical acaricides, allied with public health concerns about pesticide residues, has motivated the search for alternative control measures to suppress the pest. Hyphomycetous fungi are promising agents for mite control and the fungus Beauveria bassiana (Bb) (Balsamo) Vuillemin was investigated in this study as a biocontrol agent. The principal objectives of this study comprised: a) screening Bb strains for their pathogenicity against T. urticae; b) testing the effect of adjuvants on the efficacy of Bb; c) studying the effect of plant type on persistence of Bb and the efficacy of control of Bb against T. urticae; d) evaluating the field efficacy of Bb applications against T. urticae; e) testing the compatibility of Bb with selected fungicides; and f) assessing the synergy between Bb and soluble silicon for T. urticae control. Screening bioassays of sixty-two strains of Bb identified the two most effective strains, PPRI 7315 (R289) and PPRI 7861 (R444), that caused mortality levels of more than 80% of adult mites at 9 d post-inoculation with 2 × 108 conidia ml-1. These strains performed significantly better than the Bb commercial strain PPRI 5339, in laboratory bioassays. The two strains also attacked mite eggs, causing 53.4% and 55.5% reduction in egg hatchability at 2 × 108 conidia ml-1 respectively. However, PPRI 7861 showed relatively higher production of conidia in culture and was, therefore, selected for further trials under greenhouse and field conditions. Greenhouse evaluations of the effects of two adjuvants (Break-thru® and a paraffin oil-based emulsion) on efficacy of Bb demonstrated a higher efficacy of the biocontrol agent (BCA) when it was applied with Break-thru® or the oil solution than with water alone. Moreover, Bb conidia applied in Break-thru® solution resulted in greater control of TSM than conidia applied in the mineral oil. There was also a dose-response effect and the control of TSM by Bb increased when the concentration of conidia was increased. The control of TSM by Bb in beans (Phaseolus vulgaris L), cucumber (Cucumis sativus L.), eggplant (Solanum melongena L.), maize (Zea mays L.) and tomato (Solanum lycopersicum L.) was tested in greenhouse trials. On these crops, the persistence of conidia declined over time. The rate of decline was significantly higher on maize. However, TSM mortality was positively correlated with the amount of conidia deposited on leaves immediately after spraying, rather than their persistence over time. Higher levels of mortality of TSM due to Bb application were observed on beans, cucumber and eggplants, suggesting that the type of crop must be taken into consideration when Bb is applied as a BCA. Field efficacy of Bb against mites was evaluated in two trials on eggplants. Based on assessment of population densities of mites and leaf damage assessments; both trials showed that the strain PPRI 7861 controlled TSM in the field. Two commonly used fungicides, azoxystrobin and flutriafol, were investigated in vitro tests on culture medium and laboratory bioassays on detached bean leaves (Phaseolus vulgaris L.) for their effects on Bb. Azoxystrobin (a strobilurin) was less harmful to Bb while flutriafol was found to be inhibitory. Another important finding of this study was the substantial enhancement of Bb efficacy by soluble silicon. When Bb was combined with soluble Si, the control of TSM was better than when either of the two products was applied alone. Moreover, application of soluble Si as a plant fertilizer in hydroponic water nutrient increased accumulation of peroxidase, polyphenoloxidase and phenylalanine ammonia-lyase enzymes in leaves of plants infested with TSM. Increased activity of these defense enzymes in leaves deters feeding behaviour of mites. We suggested that feeding stress renders them susceptible to Bb infection, which would explain the synergy observed between the two agents. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.