Thesis (M.Sc. Agriculture (Agronomy) -- University of Limpopo, 2019 / Most sweet potato-producing regions in South Africa are heavily infested by the root knot (Meloidogyne species) nematodes, which are difficult to manage since the withdrawal of the highly effective fumigant synthetic chemical nematicides. Prior to the withdrawal, the management of Meloidogyne species was not a priority in sweet potato (Ipomoea batatas L.) production since methyl bromide was highly effective in suppressing nematodes. The withdrawal resulted in the introduction of various alternative nematode management strategies, with nematode resistance being the most preferred. However, progress in the use of nematode resistance had been hindered by limited information on accurate species identification since Meloidogyne species have a wide host range and some biological races. The objectives of the study were (1) to determine the degree of nematode resistance in sweet potato cv. 'Mafutha' to M. javanica, M. incognita races 2 and M. incognita race 4 and (2) to investigate the mechanism of resistance in sweet potato cv. 'Mafutha' to M. javanica, M. incognita race 2 and M. incognita race 4. A total of six Experiments were conducted. In each, treatments comprised 0, 25, 50, 125, 250, 625, 1250, 3125 and 5250 eggs and second-stage juveniles (J2), arranged in a randomised complete block design (RCBD), with six replications. Uniform rooted sweet potato cuttings were transplanted in 20-cm-diameter plastic pots filled with steam pasteurised (300˚C for 1 hour) loam soil and Hygromix-T mixed at 3:1 (v/v) ratio. At 56 days after inoculation, plant variables and nematodes in roots were collected. Meloidogyne javanica inoculum levels in Experiment 1 had highly significant (P ≤ 0.01) effects on dry shoot mass and, stem diameter, contributing 74% and 50% in total treatment variation (TTV) of the respective variables, whereas under M. incognita race 2 inoculum levels contributed 70% and 56% in TTV of dry root mass and dry shoot mass, respectively. Meloidogyne incognita race 4 inoculum levels contributed 65% xx and 58% in TTV of stem diameter and dry shoot mass, respectively. In Experiment 2, M. javanica treatment levels contributed 56% in TTV of dry root mass, whereas M. incognita race 2 inoculum levels had no significant effect on any plant variable. In contrast, M. incognita race 4 contributed 51% in TTV of vine length. In Experiment 1, the nematode levels had significant effects on reproductive potential (RP) values, with treatments contributing 96%, 86% and 76% in TTV of RP values in M. javanica, M. incognita race 2 and M. incognita race 4, respectively. In Experiment 2, treatments contributed 79%, 46% and 61% in TTV of RP values in the respective Meloidogyne species. Results of the study suggested that growth of sweet potato cv. 'Mafutha' was affected by nematode infection, whereas the test nematodes were able to reproduce and develop on the test potato cultivar. In conclusion, sweet potato cv. 'Mafutha' was susceptible to M. javanica, M. incognita race 2 and M. incognita race 4 and therefore, the cultivar should not be included in crop rotation programmes intended to manage tropical Meloidogyne species and races in Limpopo Province, South Africa. Since the cultivar was susceptible to the test nematodes, the study did not evaluate the mechanism of resistance. / Agricultural Research Council (ARC), National Research Foundation (NRF) and the Land Bank Chair of Agriculture

Thesis (M.A. Agriculture. (Plant Production)) -- University of Limpopo, 2021 / Root-knot (Meloidogyne species) nematodes are host to most plant species, with the success of most crops being dependent upon proper nematode management tactics. Sweet potato (Ipomoea batatas L.) is highly susceptible to root-knot nematodes, with physical damage being visible on roots. The withdrawal of highly effective fumigant synthetic nematicides from the agrochemical markets resulted in a need to investigate alternative strategies for managing high nematode population densities, with the use of nematode resistance being the most preferred strategy. The objectives of this study were (1) to establish whether sweet potato cv. 'Blesbok' would be resistant to M. javanica under greenhouse conditions, (2) to investigate whether cucurbitacin containing phytonematicides would be comparable to Velum synthetic nematicide in suppressing Meloidogyne species. For Objective 1, treatments comprised 0, 5, 25, 125, 625, 3125 and 15625 eggs and second-stage juveniles (J2), had six replications and validated in time. Uniform sweet potato cuttings were transplanted in 20-cm diameter plastic pots, filled with steam pasteurised (300°C for 1 hour) loam soil. At 56 days after inoculation, plant growth, plant nutrient and nematode variables were assessed using analysis of variance and subjected to lines of the best fit. Treatments had significant (P ≤ 0.05) effects on eggs and highly significant (P ≤ 0.01) effects on J2, final nematode population densities (Pf) and the reproductive factor (RF), contributing 39, 45, 42 and 92% in total treatment variation (TTV) of the respective variables. Treatments did not have significant effects on plant variables. Calcium, K, Mg and Fe versus M. javanica levels each exhibited negative quadratic relations, with the models being explained by associations from 59 to 96%. In contrast, Zn versus M. javanica levels exhibited positive quadratic relation, with the model being explained by 80 and 98% association and optimised at 125 M. javanica units. For Objective 2, four treatments, namely, untreated control, Nemarioc-AL phytonematicide, Nemafric-BL phytonematicide and Velum had 10 replications and also validated in time. The plantlets with well-developed root system were transplanted under field conditions. Data for Object 2 did not comply with the requirements for ANOVA and were therefore subjected to Principal Component Analysis (PCA). Nemafric-BL phytonematicide treatment in both experiments reduced eggs, J2 in roots and J2 in soil and RP of Meloidogyne species, with the results being comparable to those of Velum synthetic nematicide. Nemarioc-AL phytonematicide reduced J2 in roots and in soil of Meloidogyne species, without affecting eggs in roots and RP. Nemafric-BL phytonematicide and Velum each increased plant growth variables in Experiment 1 and Experiment 2, whereas Nemarioc-AL phytonematicide did not have significant effects on plant growth variables. Velum chemical nematicide stimulated the accumulation of most essential nutrient elements in leaf tissues of the test cultivar, followed by Nemafric-BL phytonematicide, whereas Nemarioc-AL phytonematicide had no significant effects on the accumulation of essential nutrient elements. The study had two major outcomes, namely, (1) that the efficacy of Nemafric-BL phytonematicide was comparable to that of Velum chemical nematicide in suppression of population densities of Meloidogyne species in cv. ′Blesbok′ under field conditions and (2) that cv. ′Blesbok′ was tolerant to M. javanica and therefore, it was not necessary to investigate the mechanisms of nematode resistance. / Agricultural Research Council (ARC) and National Research Foundation (NRF)

Thesis (M. Agric. (Plant Protection)) -- University of Limpopo, 2019 / Damage and significant losses of potato cultivar due to Meloidogyne incognita has become a serious challenge, after the withdrawal of synthetic chemical nematicides due to their environment-unfriendliness. Various alternatives have been investigated each with a wide range of drawbacks. Most phytonematicides were highly phytotoxic to crops, while their effects on nematode suppression were highly variable. The use of Nemarioc-AG phytonematicide at pre- and post-emergence would help in determining the level that is effective in supressing M. incognita without being phytotoxic. The objective of this study was to determine whether Nemarioc-AG phytonematicide could serve as pre- and post-emergent phytonematicide without inducing phytotoxicity while suppressing population densities of M. incognita. For achieving this objective, treatments, namely, 0, 2, 4, 8 and 16 g of Nemarioc-AG phytonematicide, were arranged in a randomised complete block design (RCBD), with 7 replicates. Potato seed tubers were sown into 20 cm pots, Nemarioc-AG phytonematicide placed above the tubers and covered with soil, after initiation of treatments 5 000 eggs and second stage juveniles (J2) of M. incognita per plant were inoculated. For post-emergent, treatments, replications and design were the same as in pre-emergent. Potato seed tubers were sown and inoculated with 5000 eggs and second-stage juveniles (J2) of M. incognita per plant after 100% emergence. Nemarioc-AG phytonematicide were applied 7 days after inoculation. Trials were conducted in autumn (February-April) 2017 (Experiment 1) and repeated in autumn 2018 (Experiment 2). Plant growth variables and selected nutrient elements were collected and analysed using the Curve Fitting Allelochemical Response Data (CARD) model and lines of best fit, respectively. In pre-emergent application, Experiment 1, MCSP was established at 1.95 g, with the overall xii sensitivity (∑k) being equal to zero. Therefore, in Experiment 1 and Experiment 2, all nutrient elements to increasing concentration of Nemarioc-AG phytonematicide exhibited negative quadratic relations. In both Experiments, nematode variables over increasing concentration of Nemarioc-AG phytonematicide on potato exhibited negative quadratic relations, except in Experiment 1, where J2 in roots exhibited positive quadratic relations, with models ranging between 72 to 99%. In post emergent, Experiment 1, MCSP was established at 1.57 g, with the overall sensitivity (∑k) being equal to 2. In Experiment 1 and Experiment 2, nutrient elements over increasing concentration of Nemarioc-AG phytonematicide exhibited positive and negative quadratic relations, with models ranging from 89 to 97%. In Experiment 1, nematode variables over increasing concentration of Nemarioc-AG phytonematicide exhibited negative quadratic relations, with models ranging between 92 and 98%. Positive and negative relations suggested that the product stimulated and inhibited plant growth or accumulation of selected essential nutrient elements, respectively. Increasing concentration of Nemarioc-AG phytonematicide had stimulated certain plant variables and inhibited population densities of M. incognita in pre- and post emergent application; therefore, this product was suitable for use as pre- and post emergent in management of nematodes on the test crop.

Thesis (M. Agric. (Plant Protection)) -- University of Limpopo, 2019 / Plant extracts exhibited broad spectrum of activities against root-knot (Meloidogyne species) nematodes and had long been considered as an attractive alternative due to their being biodegradable and posing limited risk hazards to the environment, animal and human health. Additionally, the materials had been dubbed as being of low-input costs and had been viewed as being easy to apply in agricultural systems. The objective of the current study was to investigate the efficacy of paint-brush flower (Kleinia longiflora) either as fermented or granular formulations on suppression of M. javanica and their related effects on growth of tomato (Solanum lycopersicum) plants under field and greenhouse conditions. Fermented crude extracts were applied at 0, 2, 4, 8, 16, 32 and 64%, whereas granular materials were applied at 0, 2, 4, 6, 8, 10 and 12 g. Regardless of the product, the treatments were arranged in randomised complete block design (RCBD), with 12 replications. Kleinia longiflora plants were collected from the wild, chopped into pieces, oven-dried at 52⁰C and fermented in effective microorganisms (EM) for 14 days, whereas the remained were retained for use as granular formulation. Tomato seedlings cv. ꞌFloradadeꞌ were used as test plants inoculated with 2500 eggs and second-stage juveniles (J2) of M. javanica. At 56 days after the treatments, nematode and plant variables were collected, prepared using appropriate methodologies and subjected to analysis of variance using Statistix 10.0 software to generate means. Plant variables were subjected to the Curve-fitting Allelochemical Response Data (CARD) computer-based model to generate appropriate biological indices. Nematode and mineral elements variable means were subjected to lines of the best fit. Findings showed second-stage juveniles (J2) in roots, J2 in soil, eggs and Pf under increasing concentration were highly significant and exhibited negative quadratic relationship. The model explained the associations by 82, xvii 81, 74 and 76%, respectively. In granular formulation, the product had no significant effects on nematode population densities. The fermented crude extracts significantly affected and exhibited positive quadratic relations for dry fruit mass, chlorophyll content, dry shoot mass, number of flowers, plant height, number of fruit and stem diameter of tomato plants. The model explained the relationship by 97, 94, 95, 96, 94, 97 and 96%, respectively. In contrast, in granular formulation, the product had significant effects and positive exhibited quadratic relations on Chlorophyll content under field and greenhouse, plant height, dry root mass and dry shoot mass. The model explained the relationships by 52, 45, 56, 47 and 59%, respectively. Plant variables and increasing concentration of the products exhibited density-dependent growth patterns for both formulations, with overall sensitivity (∑k) values of 1 and 11, respectively. In fermented liquid and granular formulations, the Mean Concentration Stimulation Point (MCSP) values were derived at 1.97% and 2.84 g, respectively. The increasing concentration of fermented K. longiflora also had significant effects and exhibited negative quadratic relations on the accumulation of K, Na and Zn in leaf tissues of tomato plants. The model explained the associations with 87, 94 and 94%, respectively. In conclusion, the findings in the current study suggested that the nematicidal chemicals in K. longiflora could not be released through irrigation water but could be released into solution through microbial degradation. Also, at low concentration suitable for use without inducing phytotoxicity, the products in either formulation could improve the accumulation of certain nutrients in leaf tissues of tomato plants.

No description available.

Root-knot nematodes (RKN) are plant parasites, and a major agricultural pest. RKN are adept at invading and feeding on plant tissue with secretions they release from their gland cells. This thesis compares glandular development in Meloidogyne to the model nematode, Caenorhabditis elegans. Pharyngeal and gland important transcription factors, PHA-4 and HLH-6, respectively, were examined for their role in regulation of parasite-specific genes. Homologues of these genes were identified and sequenced from M. incognita. Phylogenetic analyses revealed a new PPN-specific gene, hlh-6-like. Bioinformatic comparisons of the homologues revealed conservation of the DNA-binding motifs of Ce-HLH-6 and Mi-HLH-6 proteins, as well as conservation of their promoter regions. While HLH-6 antibodies proved inconclusive, expression assays revealed expectant levels of PHA-4 and HLH-6 in Meloidogyne as compared to C. elegans. In identifying genes essential for parasitism we are providing new targets for knockdown during RKN infection. / October 2016

Thesis (M. Sc. (Biochemistry)) -- University of Limpopo, 2003 / Refer to document / National Research Foundation (NRF)

No description available.

Thesis (Ph. D. in Plant Pathology)--Washington State University, May 2008. / Includes bibliographical references.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Plant Pathology, 1978.