Thesis (MSc. (Horticulture)) -- University of Limpopo, 2016. / Pelargonium sidoides has numerous medicinal applications, with economic potential to serve as a future cultigen in smallholder farming systems. However, it is highly susceptible to the root-knot (Meloidogyne species) nematodes, without any identifiable nematode resistant genotypes. Nemarioc-AL and Nemafric-BL phytonematicides, with cucurbitacin A and cucurbitacin B active ingredients, respectively, are being researched and developed as an alternative to synthetic nematicides at the University of Limpopo. However, since active ingredients in phytonematicides are allelochemicals, the two phytonematicides have the potential of inducing phytotoxicity on crops protected against nematode damage. The objectives of the study, therefore, were (1) to determine the non-phytotoxic concentration of Nemarioc-AL phytonematicide on plant growth of P. sidoides, and (2) to determine the non-phytotoxic concentration of Nemafric-BL phytonematicide in plant growth of P. sidoides. Cuttings were raised in 30-cm-diameter plastic pots containing 10 000 ml steam-pasteurised river sand and Hygromix-T at 3:1 (v/v) under microplot conditions in autumn (March-May) and repeated in spring (August October) 2015. After establishment each plant was inoculated with 5 000 eggs and second-stage juveniles (J2s) of M. javanica. Six treatments, namely, 0, 2, 4, 6, 8 and 10% concentrations of each phytonematicide on separate trials were arranged in a randomised complete block design, with seven replicates. At 56 days after inoculation, in Experiment 1, Nemarioc-AL phytonematicide, treatment significantly (P ≤ 0.05) affected plant height, dry root mass and root galls, contributing 62, 69 and 70% to total treatment variation of the three variables, respectively. Relative to untreated control Nemarioc-AL phytonematicide increased plant height and dry root mass by 34 to 61% xxi and 20 to 76%, respectively, with a slight decrease by 5% in plant height at the highest concentration. However, the material decreased root galls by 5 to 50%. Significant (P ≤ 0.05) plant variables were subjected to Curve fitting-allelochemical respond dosage model, to generate biological indices which were used to compute the mean concentration stimulation point (MCSP) using the relation: MCSP = Dm + Rh/2 and the overall sensitivity value (∑k). In Experiment 1, MCSP = 6.18% and ∑k = 3. Plant variables and increasing concentration of phytonematicide exhibited quadratic relations. Treatments reduced nematode variables, at all levels including at the lowest, but the effect were not different. In Experiment 2, Nemarioc-AL phytonematicide treatment effects were not significant on plant variables except for root galls, but were significant for root nematodes except for eggs. Data for plant variables in Experiment 2 were not subjected to Curve fitting-allelochemical respond dosage model because they were not significant (P ≤ 0.05). In Experiment 1, Nemafric-BL phytonematicide treatment significantly (P ≤ 0.05) affected plant height and root galls, contributing 63 and 67% to total treatment variation of the two variables, respectively. Relatively to untreated control, plant height was increased by 10 to 36%, while root galls was reduced by 2.43 to 60%. In Experiment 1, MCSP = 2.87% and ∑k = 3. Concentrations of Nemafric-BL phytonematicide significantly (P ≤ 0.05) reduced eggs, juveniles and Pf at all levels including at the lowest, but the effect were not significant different, with treatments contributing 78, 72 and 90% to the total treatment variation. In Experiment 2, Nemafric BL phytonematicide treatment effects were not significant on plant variables except for root galls, but were significant for root. In conclusion, Nemarioc-AL and Nemafric-BL xxii phytonematicides could be applied at the lowest concentration of 2% where it was shown to be effective in suppressing population densities of M. javanica. / Agricultural Research Council (ARC), National Research Fund (NRF) , Flemish Inter university Council of Belgium and Land Bank Chair of Agriculture ─ University of Limpopo

Thesis (M.Sc. (Agriculture, Plant Protection)) -- University of Limpopo, 2020 / The unavailability of environment-friendly nematicides for managing root-knot (Meloidogyne species) nematodes in crop husbandry have led to various alternative methods being sort which includes the development of cucurbitacin-containing phytonematicides. The cited phytonematicides consistently suppressed nematode numbers on different crops under greenhouse, microplot and field conditions, although there is lack of information on how the products would affect susceptible Swiss chard infected by root-knot nematodes. Swiss chard is one of most nutritious vegetables, grown throughout the year and is well adapted to different soil types. However, these products have the potential to induce phytotoxicity on various crops, if applied improperly. Phytotoxicity of phytonematicides on different crops, has been resolved by deriving 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 objectives of this study were to investigate (1) whether population densities of Meloidogyne species, growth and accumulation of selected nutrient elements in Swiss chard would respond to increasing concentration of Nemarioc-AL and Nemafric-BL phytonematicides under greenhouse and microplot conditions and (2) whether the nemarioc-group and nemafric-group phytonematicides in liquid and granular formulations would affect population densities of Meloidogyne species and the productivity of Swiss chard with related accumulation of nutrient elements in leaf tissues under field conditions. Parallel experiments for Nemarioc-AL and Nemafric-BL phytonematicides were conducted concurrently under greenhouse and microplot conditions. Greenhouse experiment was prepared by arranging 25-cm-diameter plasticpods on greenhouse benches, whereas microplot experiment was prepared by digging holes and inserting 30-cm-diameter plastic pots in the field. The four-week-old Swiss chard seedlings were transplanted into the pots, filled with steam-pasteurised loam, sand and Hygromix-T at 3:1:1 (v/v) ratio. Treatments comprised 0, 2, 4, 8, 16, 32 and 64% phytonematicides arranged in randomised complete block design (RCBD), with six replications. Treatments were applied seven days after inoculation, with 3000 eggs and J2 of M. incognita race 4 under greenhouse conditions, whereas under microplot conditions were inoculated with 6000 eggs and J2 of M. javanica. Under field conditions, treatments comprised untreated control (0), 2 g Nemarioc-AG and 3% Nemarioc-AL phytonematicides (nemarioc-group) or 0, 2 g Nemafric-BG and 3% Nemafric-BL phytonematicides (nemafric-group), arranged in RCBD, each experiment with 8 replications. At 56 days after initiation of treatments, eggs in roots, J2 in roots and Pf exhibited negative quadratic relations under both greenhouse and microplot conditions. Under greenhouse conditions, dry shoot mass (R2 = 0.81), dry root mass (R2 = 0.87) and leaf number (R2 = 0.91) over Nemarioc-AL phytonematicide exhibited positive quadratic relations. In contrast, dry shoot mass (R2 = 0.78), dry root mass (R2 = 0.93) and leaf number (R2 = 0.70) over Nemafric-BL phytonematicide exhibited positive quadratic relations. Under microplot conditions, dry shoot mass (R2 = 0.95) and gall rating (R2 = 0.96) over Nemarioc-AL phytonematicide, exhibited positive quadratic relations. Dry shoot mass (R2 = 0.84) and gall rating (R2 = 0.97) versus Nemafric-BL phytonematicide exhibited positive quadratic relations. Selected nutrient elements under greenhouse conditions K (R2 = 0.96), Ca (R2 = 0.79), Mg (R2 = 0.64), Fe (R2 = 0.78) and Zn (R2 = 0.77) over Nemarioc-AL phytonematicide exhibited positive quadratic relations. In contrast, only Ca (R2 = 0.90), Mg (R2 = 0.68) and Zn (R2 = 0.84) over Nemafric-BL phytonematicide exhibited positive quadratic relations, whereas K (R2 = 0.72) and Fe (R2 = 0.63) over the product exhibited negative quadratic relations. Under microplot conditions, K (R2 = 0.82), Ca (R2 = 0.90) and Mg (R2 = 0.98) over Nemarioc-AL phytonematicide exhibited positive quadratic relations, whereas Fe (R2 = 0.91) and Zn (R2 = 0.79) over the product exhibited negative quadratic relations. In contrast, K (R2 = 0.60), Ca (R2 = 0.68) and Zn (R2 = 0.95) over Nemafric-BL phytonematicide exhibited positive quadratic relation, whereas Mg and Fe over the product did not have significant relationships. Under greenhouse conditions, MCSP values for Nemarioc-AL and Nemafric-BL phytonematicides on Swiss chard were 3.03 and 2.36%, whereas overall sensitivity (∑k) values of the crop to the product were 3 and 0 units, respectively. In contrast, MCSP values of Nemarioc-AL and Nemafric-BL phytonematicides on Swiss chard under microplot conditions was successfully established at 3.71 and 3.33%, whereas the ∑k values were 2 and 1 units, respectively. Under field conditions, at 64 days after initiating the treatments, the nemarioc-group phytonematicides had highly significant effects on eggs in roots and reproductive potential (RP), contributing 79 and 77% in total treatment variation (TTV) of the respective variables. In contrast, the nemafric-group phytonematicides had highly significant effects on eggs in roots and RP, contributing 67 and 76% in TTV of the respective variables. Under field conditions, all plant growth variables were not significantly affected by the treatments. The nemarioc-group phytonematicides had significant effects on K and Mg in leaf tissues of Swiss chard, contributing nemafric-group phytonematicides had significant effects on Mg, contributing 62% in TTV of the variable. In conclusion, the products could be used on Swiss chard for managing population densities of Meloidogyne species. However, due to the sensitivity of Swiss chard to the products, it would be necessary to use the derived MCSP values to determine the application intervals of the products on the test cultigen / National Research Foundation (NRF) Agricultural Research Council (ARC)

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

Potato (Solanum tuberosum) is regarded as one of the single most important vegetable crops in South Africa, with an average annual production of 2 million metric tons. The potato industry contributes to an average of $ 0.37b worth of potatoes annually. Over the years, potato production in South Africa has been affected by, among other factors, diseases and plant parasitic nematodes particularly root-knot nematodes (Meloidogyne spp.). In infected potato fields, root-knot nematodes cause great damage to the crop leading to substantial losses in yield and compromised produce quality. The direct and indirect damage caused by Meloidogyne species results in revenue loss due to a high number of table and processing potatoes rejected in markets both locally and internationally. The presence of resistance breaking Meloidogyne populations, the withdrawal of methyl bromide and lack of commercially grown resistant cultivars suggests that growers are likely to experience more losses in the future. Furthermore, distribution of seed tubers harbouring root-knot nematodes, which may also be asymptomatic, inadvertently facilitates transmission of these parasites to new areas thus perpetuating the problem. Therefore, for the potato industry to adequately address the threat of root-knot nematodes, accurate identification and quantification of root knot nematode levels in the field as well as in seed tubers is of importance. Currently most methods of identifying Meloidogyne species largely rely on the use of morphological traits. However, it can be a challenge to accurately differentiate between closely related species using morphology and other classical methods. To resolve this, recent trends globally have focused on the development of DNA-based diagnostics to rapidly and accurately identify different Meloidogyne species. This study therefore sought to; (a) develop a PCR-based diagnostic tool for accurate detection and identification of various Meloidogyne species parasitizing potatoes in South Africa; (b) use this tool to map their distribution and; (c)develop real-time PCR (qPCR) techniques for accurate quantification and characterization of tropical Meloidogyne species from infected potato tubers. In this study, of the 78 composite potato tuber samples collected from various potato growing regions across seven provinces, 24% were found infected with M. javanica, 23% with M. incognita, 17% with M. arenaria, 14% with M. enterolobii, 3% M. chitwoodi, 1% M. hapla and 1% as M. artiellia. The identity of the remaining 17% could not be established. The three tropical species; M. javanica, M. incognita and M. arenaria were identified as the dominant species, occurring almost in every region sampled. Meloidogyne hapla and M. enterolobii occurred in Mpumalanga and KwaZulu–Natal respectively while M. chitwoodi was isolated from two growers located within the Free State. In the study the use of HRMC and real-time PCR was also developed for identification and quantification of tropical Meloidogyne species infesting potato tubers. Using these two techniques, we were able to show that Meloidogyne arenaria populations produced specific melting peaks (79.3183± 0.0295°C, P < 0.05) thus distinguishing themselves from M. incognita (79.5025± 0.0224°C, P < 0.05) and M. javanica (79.96 ± 0.0459°C, P < 0.05). Real-time PCR was also able to detect 1.53/100th of a nematode using second stage juveniles. / Dissertation (MSc)--University of Pretoria, 2012. / Microbiology and Plant Pathology / unrestricted

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

Orientador: Leonardo Bianco / Resumo: Sendo a beldroega uma planta infestante da cultura do tomate e uma hospedeira natural de nematoides do gênero Meloidogyne, levanta-se a hipótese de que a ocorrência dessa planta daninha em áreas de plantios de tomate possa interferir no crescimento e produtividade do tomateiro, dependendo do período de convivência, e que existe uma relação da sua ocorrência com a infestação de M. incognita no tomateiro, e que é possível controlá-la com seletividade ao tomateiro. Dessa forma, com este estudo, objetivou-se: a) avaliar se há interferência da beldroega no crescimento e produtividade do tomateiro; b) determinar o período de convivência da planta daninha com a cultura que não afete o crescimento e a produtividade do tomateiro; c) avaliar se a beldroega infestando a cultura do tomate atua como hospedeira de Meloidogyne javanica e com isso reduz a sua infestação no tomateiro; d) estudar a seletividade de herbicidas ao tomateiro visando o controle da beldroega em pré e pós-emergência e) verificar se a velocidade de controle do metribuzim elimina de imediato a interferência dessa planta daninha no tomateiro. Para tanto, esse estudo constou de três experimentos. No primeiro, os tratamentos experimentais consistiram de três períodos de convivência do tomateiro „Dylla‟ com a beldroega (14, 21 e 60 dias após o transplantio), com um tratamento para tomate sem convivência com a planta daninha e outro tratamento para a beldroega sem convivência com a cultura, todos com ou sem a inoculação de ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Purslane is an infesting plant in tomato culture and a natural host of nematodes of the genus Meloidogyne, the hypothesis arises that the occurrence of this weed in tomato plantation areas may interfere in tomato growth and productivity depending on the period coexistence between them. Also that is a relationship between it ́s occurrence and the infestation of M . incognita in tomato and that it is possible to control it with tomato selective products. This study aimed to: a) assess whether purslane interferes with tomato growth and productivity; b) determine the period of coexistence of the weed with the crop that does not affect the growth and productivity of the tomato; c) to evaluate whether purslane infesting the tomato crop acts as host of Meloidogyne javanica and thereby reduces its infestation in tomato; d) to study the selectivity of herbicides for tomato aiming at the control of purslane in pre and postemergence e) to verify if the speed of control of the metribuzim immediately eliminates the interference of this weed in the tomato. This study consisted of three experiments. In the first, the experimental treatments consisted in three coexistence periods of tomato 'Dylla' with purslane (14, 21 and 60 days after transplanting), with a treatment for tomatoes without living with weeds and another treatment for purslane without coexistence with culture, all with or without Meloidogyne javanica inoculation. The treatments were arranged in a randomized block design, in 6 ... (Complete abstract click electronic access below) / Mestre

Thesis (Ph.D. Agriculture (Plant Production)) -- University of Limpopo, 2020 / Worldwide, both root-knot (Meloidogyne species) and sugarcane aphid (Melanaphis sacchari Zehntner), are economic pests on sugarcane and sorghum crops. In most cases, each of the two pests is managed using host plant resistance due to the economic benefits derived from this management strategy. The highly nematode resistant sweet stem sorghum (Sorghum bicolor L.) cv. 'Ndendane-X1' used in ethanol production, is highly sensitive to sugarcane aphid, with some indication that the latter could interfere with nematode resistance in the sorghum cultivar. This study had four objectives which collectively intended to investigate the interactive effects of infection by three Meloidogyne species and infestation by aphid under different conditions on resistance to nematode in a nematode-resistant sorghum cultivar. The research objectives were achieved through four trials. In each trial a 2 × 2 factorial experiment, each with and without nematode and aphid as first and second factors, respectively, were conducted. Treatments were arranged in a randomised complete block design, with six replications, and each experiment validated in time. At 150 days, after emergence, the nematode × aphid interaction significantly reduced sucrose by 17, 74 and 42% in Meloidogyne enterolobii, Meloidogyne incognita and Meloidogyne javanica trials, respectively. Aphid infestation of sorghum significantly increased the reproductive potentials of the three respective Meloidogyne species by 196, 320 and 152%, but significantly, reduced plant growth variables from 20-44 and 48-51% in two respective trials. The mineral nutrients S and Zn were reduced in leaf tissues of the test cultivar in Trial 1, whereas Ca and Zn were respectively reduced by 24 and 51% in Trial 2 and by 52 and 51% in Trial 3. Since the reproductive potential values for Meloidogynqe species on the test sorghum cultivar were greater than unity and nematode infection reduced the plant variables, cv. 'Ndendane-X1' lost resistance to xx the test Meloidogyne species. In achieving Objective 2, procedures were similar to those in Objective 1 except that the study was conducted under field conditions under mixed nematode populations of M. enterolobii, M. incognita and M. javanica. Sorghum seedlings were raised at 0.3 m × 0.3 m inter and intra row spacings. Soon after emergence, plants were thinned to one per station, randomly selected for nematode and nematode-aphid treatments. Mixed populations of Meloidogyne species (M. enterolobii, M. incognita and M. javanica) at approximately 1:1:1 (v/v) ratio were applied at 300 eggs + J2 per plants after thinning at the five plants which were used as nematode alone treatments. The latter were also infested with 20 sugarcane aphids to constitute a nematode + aphid treatments. Buffer zone plants separating the treatments were monitored for aphids and stock borer, which were sprayed when necessary. At 150 days after infestation, relative to nematode alone, nematode-aphid significantly reduced degrees Brix from 13% to 61%, but significantly increased the reproductive potential of mixed Meloidogyne species and root galls by 279 and 199%, respectively. Also, the combined effect significantly reduced plant growth variables from 35 to 55% and the mineral nutrient elements in leaf tissues of the cultivar from 33 to 73%. At 150 days after the treatment, the second and first order interaction (Nemarioc-AL × Nemafric-BL × Mordica and Nemafric-BL × Mordica) had significantly increased sucrose content from 48 to 66%, increased plant growth variables from 49 to 163%, increased accumulation of certain nutrient elements from 164 to 206%. The terpenoid-containing phytonematicides could have potential future application in the husbandry of ethanol-producing sweet stem sorghum cultivars in relation to increasing sucrose above the 16% minimum for premium delivery fees and increased plant growth. Under field conditions, in pest-free condition (Objective 3), drenched terpenoid-containing phytonematicides significantly increased sucrose content at xxi middle and bottom part of SSS cv. 'Ndendane-X1' by 66 and 48%. However, these products did not significantly increase plant variables, except tiller number, which was increased by 163 under first order interaction from Nemafric-BL and Mordica phytonematicides. Similarly, nutrient elements variables had generally not been increased by the interaction of these products, except Ca and K, which were increased by 206 and 164%. In achieving Objective 4, a 2 × 2 × 2, with the first, second and third factor being Nemarioc-AL (with and without), Nemafric-BL (with and without) and Mordica (with and without) phytonematicides, respectively. on sorghum cultivar infected with a mixture of Meloidogyne species and infested with aphids, under microplot conditions, untreated control sucrose content remained below the standard of 16 degrees Brix, whereas the second order interaction increased the variable far above the standard, along with various plant growth variables also increased. However, both nematode and aphid population densities were significantly reduced by the interactions. Findings in this thesis constituted the first report where aphid infestation broke resistance to Meloidogyne species in sweet stem sorghum cv. 'Ndendane-X1'. Therefore, the successful use of nematode resistance in the cultivar in areas with high nematode population densities would depend upon the effective management of the sugarcane aphid population densities. Also, the three terpenoid-containing phytonematicides would when combined or used alone have the potential future in the husbandry of sweet stem sorghum cultivars intended for ethanol production and suppression of nematode population densities / 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.

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