Limited information exists on the occurrence and distribution of plant nematodes in subsistence maize-producing agricultural areas of South Africa. A nematode survey was thus conducted during summer 2023 in three maize-producing areas each of the Eastern Cape, Mpumalanga and Limpopo Provinces of South Africa, to assess the occurrence and distribution of plant nematodes over one season. Results demonstrated that root-knot (Meloidogyne javanica, M. incognita) and root-lesion (Pratylenchus zeae) nematodes are the most abundant nematode groups in sampled maize fields followed by spirals (Rotylenchus brevicaudatus, Helicotylenchus dihystera, H. multicinctus) and reniform nematode (Rotylenchulus parvus). Ten other plant-parasitic nematode genera in order of predominance included Hemicriconemoides, Dolichodoridae, Aphelenchus, Scutellonema, Dorylaiminae, Scutellonema, Criconemoides, Ditylenchus, Longidorus and Xiphenema were also identified. Under mixed-species communities, M. javanica outcompeted M. incognita, whereas P. zeae outcompeted P. brachyurus. In conclusion, the low maize yields in subsistence maize-producing areas can, among other challenges, be attributed to the widespread occurrence and distribution of plant nematodes.

The successful production of biofortified sweet potato cultivars is being limited by the wide distribution of the southern root-knot nematode (Meloidogyne incognita), which is historically one of the most aggressive thermophilic Meloidogyne species. Thus, it is increasingly important to include nematode resistant germplasm in breeding biofortified sweet potato cultivars. The objective of this study was to determine the host status of 18 biofortified sweet potato lines and cultivars to M. incognita, with cv. 'Beauregard' serving as a susceptible standard at the University of Limpopo, South Africa. The experiment was conducted in spring 2023 and validated in 2024. Each line, in 20 cm-diameter pots, was irrigated with 250 ml water every other day and inoculated with 250 eggs + second-stage juveniles. Fifty-six days after inoculation, the reproductive potential (RP = total eggs + juveniles/g fresh roots) less than unity suggested that four sweet potato lines 'ARC-SP-8', FS5-2, FS1-1 and 'Khumo' were non-host to M. incognita in Experiment 1, whereas in Experiment 2, lines 2013-26-5, FS5-2-, 2015-2-1 and 'Khumo' were non-host. In conclusion, non-host germplasm to the test nematode exists in some biofortified sweet potato lines, which should further be assessed for resistance against the nematode.

Cowpea (Vigna unguiculata (L.) Walp.) is an important grain legume widely cultivated in sub-Saharan Africa for food security, nutritional supplementation, income generation, and soil fertility improvement. However, productivity of the crop is severely constrained by root-knot nematodes (Meloidogyne spp.), particularly the thermophilic species Meloidogyne incognita, Meloidogyne javanica and Meloidogyne enterolobii. The objective of this study was to determine the host status of six cowpea lines against M. javanica under greenhouse conditions. Two greenhouse experiments were conducted at the University of Limpopo, South Africa, using a randomised complete block design with six treatments replicated six times. Fourteen days after sowing, each seedling was inoculated with 3,000 eggs plus second-stage juveniles (J2) of M. javanica. Nematode assessments were conducted 56 days after inoculation. Reproductive potential (RP) was calculated as the ratio of final nematode population density to fresh root mass. Significant differences (P ≤ 0.05) were observed among cowpea lines for nematode reproduction. All test lines supported nematode reproduction, with RP values consistently exceeding unity. The findings demonstrate that all evaluated cowpea lines were susceptible hosts to M. javanica and are therefore unsuitable for deployment in crop rotation systems aimed at suppressing root-knot nematode populations. The study highlights the importance of incorporating nematode resistance screening into cowpea breeding programmes to support the development of integrated nematode management strategies under climate-smart agricultural systems.

Sweet potato (Ipomoea batatas L.) is an important staple crop valued for its high nutritional content and adaptability to adverse environmental conditions. However, its production is constrained by root-knot nematodes (Meloidogyne species), particularly Meloidogyne javanica (Treub [Chitwood]) which significantly reduce yield and quality in various crops. This study evaluated the host-status and host-sensitivity of the sweet potato cv. ‘Blesbok’ to M. javanica in a pot experiment, conducted at the Green Biotechnologies Research Centre of Excellence, University of Limpopo. A randomized complete block design with seven inoculation levels (0, 5, 25, 125, 625, 3125 and 15625 eggs + second-stage juveniles (J2) and six replications were used. Validation was done over two growing seasons. Nematode reproductive factor (RF), root galls and key plant variables were assessed at 56 days after inoculation. Meloidogyne javanica was able to establish and reproduce on ‘Blesbok’ at low inoculation levels, with RF exceeding 1, but declined to below 1 at higher inoculation levels. Variable RF values, the absence of root galls and plant variables which were not affected by nematode infection, but all suggested a degree of tolerance rather than resistance. The findings suggest that while ‘Blesbok’ can be cultivated in nematode-infested fields, integrated pest management strategies may be necessary to mitigate nematode pressure in high-density infestation areas. Future research should focus on alternative control measures to enhance the sustainability of sweet potato production in nematode-prone environments.

Sweet potato (Ipomoea batatas L.) is a valuable staple crop rich in essential nutrients such as iron (Fe), potassium (K), magnesium (Mg), and calcium (Ca). However, root-knot nematodes (Meloidogyne spp.), particularly Meloidogyne javanica (Treub) Chitwood, pose a significant threat to its productivity by affecting nutrient uptake. Despite the global prevalence of M. javanica, there is inconsistent information on its impact on the nutrient composition of sweet potato leaves. This study aimed to assess the response of selected nutrient elements (Ca, K, Mg, Fe, and Zn) in the leaf tissues of sweet potato cultivar ′Blesbok' infected by M. javanica at the University of Limpopo, South Africa, using a randomized complete block design with six replications. Seven M. javanica inoculation levels (0, 5, 25, 125, 625, 3125, and 15,625 eggs + second-stage juveniles (J2) were applied to the sweet potato plants. Nutrient element concentrations in the leaves were analysed using Inductively Coupled Plasma Optical Emission Spectrometry after a microwave digestion process. Independent variables (x-axis) were log-transformed for normality and subjected to analysis of variance, with multiple regression analysis performed. Negative quadratic relationships were observed for Ca, K, Mg and Fe, with inhibited concentrations at low nematode densities and stimulated ones at higher levels. However, Zn responded with a positive quadratic trend, indicating gradual decline under lower nematode stress. Optimal levels of Ca, K, Mg and Fe occurred at lower nematode population densities, whereas Zn accumulation peaked at higher infestation levels. In conclusion, the study confirmed that M. javanica infection disrupts nutrient accumulation in sweet potato, leading to nematode density-specific responses. Managing nematode population densities to lower levels may help to maintain optimal nutrient concentrations. The findings provide insights into the nutritional impact of nematode infections and can inform integrated nematode management strategies for sustainable sweet potato production.

Potato (Solanum tuberosum L.) does not have genotypes that are resistant to the root-knot (Meloidogyne species) nematodes and thus, were effectively managed using fumigant synthetic chemical nematicides. Since the withdrawal of the products from the agrochemical markets due to their environment-unfriendliness, Meloidogyne enterolobii (Yang and Eisenback) has emerged as a serious threat in crop rotation systems intended to manage this pest. A wide range of alternative products, viewed as being environment-friendly, are being investigated against Meloidogyne species on various crops, but with limited inter-efficacy comparisons. Thus, it was against the stated backdrop that an experiment was carried out to investigate the inter-efficacy comparison of Velum (a.i., fluopyram), Biocult (a.i. Glomus + Trichoderma spp.) and Nemafric-BL phytonematicide (a.i., cucurbitacin B) on the suppression of M. enterolobii in potato under field conditions. The initial nematode population density (Pi) averaged 13 J2/250 ml soil subsample, therefore necessitating augmentation with 100 eggs + J2 M. enterolobii in the furrow with potato tubers, with each treatment applied according to label instruction around randomly selected potato tubers, prior to covering with soil. At harvest, the treatments had significant (P ≤ 0.05) effects on eggs in root, juveniles in root and reproductive potential (RP), contributing 88, 73 and 93% in total treatment variation of the respective variables. Relative to untreated control, Velum reduced eggs in root, juveniles in root and RP by 100 38 and 62%, respectively. Biocult reduced the respective variables by 42, 37 and 71%. Similarly, Nemarioc-BL phytonematicide reduced the respective variables by 67, 70 and 48%. Although inter-efficacy variation in eggs and juveniles in root was significant (P less than 0.05), such variation was not significant on reproductive potential, with all test products significantly reducing nematode variables when compared to untreated control. In conclusion, Velum, Biocult and Nemafric-BL phytonematicide had comparable inter-efficacy effects on the suppression of M. enterolobii in potato and each product could be used in the management of nematode population densities in potato under field conditions.

Nemafric-BL phytonematicide is a potent plant-based nematicide which consistently suppress nematode population densities of root-knot (Meloidogyne species) nematodes on various crops, but with limited information on its effects on foliar nutrient elements in sweet potato. The objective of this study, therefore, was to investigate the effects of Nemafric-BL phytonematicide on accumulation of nutrient elements in leaf tissues of sweet potato cv. 'Bophelo' under greenhouse conditions in Limpopo Province, South Africa, during autumn (February-April) in 2021 and validated in 2022. The product was applied weekly at geometric concentrations, with mature leaves collected and prepared for analysis of nutrient elements at eight weeks. Seasonal interactions were not significant and therefore data were pooled (n = 70) and then subjected to the Curve-fitting Allelochemical Response Dose (CARD) algorithm computer model. Iron (R2 = 0.86), K (0.91) and Na (0.82) versus Nemafric-BL phytonematicide each exhibited negative quadratic relations, whereas Zn (0.83) versus the product exhibited positive quadratic relations. In all test elements, the CARD-generated biological indices illustrated that the accumulation of elements was highly sensitive to the concentration of Nemafric-BL phytonematicide. In conclusion, in sweet potato production, the application of Nemafric-BL phytonematicide can inhibit (Fe, K) and stimulate (Zn) the accumulation of certain elements in leaf tissues of sweet potato cv. ′Bophelo‵.

Root-knot nematodes (Meloidogyne species) are the most important group of plant nematodes in potato-producing regions of South Africa. Prior to the withdrawal of synthetic chemical fumigant nematicides from the agrochemical markets, Meloidogyne species were viewed as a minor pest in potato-producing regions. Currently, it has been established that all potato cultivars are host to Meloidogyne species, with the preferred management option of the genus being the use of resistant crops. However, the host status of most crops used in potato-based crop rotations intended to manage nematode population densities of the genus had not been established. Globally, M. incognita is viewed as being more aggressive than M. javanica, whereas in South Africa the opposite is true. Therefore, the objective of the study was to determine whether the reproduction potential (RP) values of M. javanica on 16 crops used in potato crop rotation systems would be below unity. The experiment was conducted under greenhouse conditions at the University of Limpopo during autumn (February-April) 2022 and validated in spring (September-November) of the same year in South Africa. Treatments (16 crops) were laid out in a randomized complete block design, with six replications. The crops were inoculated with 250 eggs + second-stage juveniles (J2). At 56 days after inoculation, nematodes variables were collected and expressed as RP, which demonstrated that there were similarities and differences in RP of the 16 crops to infection by M. javanica, but with the values being below one in white maluti oats, tillage radish, forage sorghum, and jap radish. In conclusion, the four crops with RP values below one could be used in a potato-crop rotation system intended to manage the population densities of M. javanica.

Root-knot (Meloidogyne species) nematode population densities on various crops, including sweet sorghum, were consistently decreased by three triterpenoid phytonematicides that are currently available as Nemarioc-AL, Nemafric-BL and Mordica. These compounds have chemically different active ingredients. The interaction between triterpenoid phytonematicides and the accumulation of nutrients in plant leaf tissues has not yet been studied, with the exception of Nemarioc-AL and Nemafric-BL. The objective of this study was to investigate the interactive effects of triterpenoid phytonematicides on accumulation of nutrient elements in leaf tissues of sweet sorghum under microplot conditions in Limpopo Province, South Africa during 2020 and 2021. Nemarioc-AL, Nemafric-BL and Mordica were laid in a 2 × 2 × 2 factorial experiment, respectively. The test treatments were arranged in a randomized complete block design, with eight replications, conducted on artificial microplots containing steam pasteurized soil. At 150 days after inoculation, the second order interaction (Nemarioc-AL × Nemafric-BL × Mordica) significantly (P=0.05) increased accumulation of Ca, K and Mg in leaf tissues of sweet sorghum, but without affecting P, Fe, Na and Zn. Relative to untreated control, second order interaction increased Ca, K and Mg by 206, 164 and 289%, respectively. In accordance with the density-dependent growth principles of entities exposed to allelochemicals, soil-drenched administration of triterpenoid phytonematicides dramatically modified the accumulation of nutritional components in leaf tissues of sweet sorghum.

Phytonematicides are being used as an alternative to synthetic chemical nematicides for managing population densities of the root-knot (Meloidogyne species) nematodes in the production of crops. However, due to their origin from allelochemicals, phytonematicides have the potential of being phytotoxic and thereby inducing unintended crop losses. The incident is being managed through a computer-based model, which provides the non-phytotoxic concentration that should be applied at each application interval, with inherent attributes of being plant-specific. The objective of this study was to investigate the non-phytotoxic concentration of Nemafric-BL phytonematicide on sweet potato cv. 'Bophelo' and associated overall sensitivity (∑k) of the cultivar to the product. The trial was initiated during autumn (February-April) 2021 and validated in 2022 in Limpopo Province, South Africa. Geometric concentrations of the product, applied weekly, were randomly assigned with five replications. At 56 days after the treatment, plant variables were collected, prepared, and subjected to the computer-assisted model, with the non-phytotoxic concentration, Mean Concentration Stimulation Point (MCSP), computed at 2.18 % Nemafric-BL for cv. 'Bophelo', with (∑k) = 0. In conclusion, the application of 2.18 % Nemafric-BL would not induce phytotoxicity to sweet potato cv. 'Bophelo'.

Priming-and-drying technology for pea (Pisum sativum L.) seeds with hypogeal germination showed that the technology could improve plant growth and development, while suppressing nematode population densities, but without information on the potential causal factors for the former. A study was, therefore, conducted in Limpopo Province, South Africa, to investigate the extent to which plant responses could be associated with accumulation of foliar nutrient elements in pea plants post-subjecting pea seeds to the technology. After a 2-h priming of pea seeds in geometric concentration of Nemarioc-AL and Nemafric-BL phytonematicides and then air-dried in ovens at 26ºC for 72 h. Seeds were sown in 20-cm-diameter plastic pots filled with appropriate growing mixture, with one trial in the greenhouse and the other on microplots. At 60 days after sowing, 10 healthy mature leaves per plant were prepared for extraction of nutrient elements through the digestion method and then quantified in Atomic Absorption Spectrophotometer ICPE-9000. Iron, Na, K and Zn in leaf tissues of pea plants versus increasing phytonematicides concentration, regardless of the growing condition, exhibited significant (P ≤ 0.05) negative or positive quadratic equations. In conclusion, results suggested that the priming-and-drying technology could affect pea plant growth through disproportionate accumulation of nutrient elements in foliar leaf tissues.

Triterpenoid phytonematicides, namely, Nemarioc-AL, Nemafric-BL and Mordica, when drench-applied each consistently suppressed root-knot nematode population densities, with limited information on whether the products could induce any systemic effects that would suppress sugarcane aphid population densities and reproductive potential. The objective of the study was therefore to determine the interactive effects of soil-drenched triterpenoid phytonematicides on aphid population densities and their reproductive factors. A 2× 2× 2 factorial experiment was laid out in a randomised complete block design with six replications during 2020-21 and 2021-22 growing seasons in Limpopo Province, South Africa. Each sweet sorghum seedling was infested with 5 adult M. sacchari, with appropriate treatment combinations drench-applied weekly. At 150 days after infestation, treatments had highly significant effects on aphid population densities and reproductive factors. Relative to untreated control, the second order interaction and the three first order interactions reduced aphid population densities by 92, 75, 79 and 80%, respectively. In conclusion, soil-drenched triterpenoid phytonematicides induced systemic effects in sweet sorghum, which significantly suppressed population densities of M. sacchari.

Globally, sweet sorghum is being used as source of ethanol. However, its sugar content is highly variable, and nematodes are suspected as the potential cause of the variability. Two cucurbitacin-containing phytonematicides were on various occasions shown to improve sugar content and plant growth of sweet sorghum cultivars, with cucurbitacins chemically classified as terpenoids. The terpenoids being tested during 2020 and 2021 as phytonematicides at the University of Limpopo, South Africa, include Nemarioc-AL, Nemafric-BL and Mordica. Although the interactive effects of Nemarioc-AL and Nemafric-BL on sugar content and plant growth had been widely investigated, the interactive effects of the products with Mordica on the test plant variables had not been documented. The eight factorial treatments, namely, untreated control, Nemarioc-AL alone Nemafric-BL alone, Mordica alone, Nemafric-BL + Mordica, Nemarioc-AL + Mordica, Nemafric-BL + Mordica and Nemarioc-AL + Nemafric-BL + Mordica, arranged in a randomised complete block design, were replicated six times in a microplot trial. At 150 days after initiating the treatments, the second order interaction increased degree Brix by 66 and 48% in the middle and bottom internodes, respectively, but without affecting plant growth variables. The latter were significantly affected by the first order interactions which excluded Mordica. In conclusion, Mordica should not be included in cropping system of sweet sorghum, where the intention includes increasing sugar content.

Commercially available potato (Solanum tuberosum) cultivars are highly susceptible to root-knot (Meloidogyne species) nematodes, without known genotype with resistance to the genus. This review shall provide an overview on some reasons where using nematode resistance technologies in crop rotations intended to manage nematode population densities results in inconsistent outcomes. The latter is primarily due to the existence of survival strategies in nematode stages and the existence of pre-and post-infectional nematode resistance mechanisms with different capabilities for reducing nematode population densities. Generally, plants with pre-infectional nematode resistance do not allow nematode juveniles to penetrate the root systems, but exude chemicals into the rhizosphere, which repel nematodes, with many entering cryptobiosis as a survival strategy. In contrast, in post-infectional nematode resistance, juveniles penetrate the root system, thereby triggering nematode resistance chemicals, which trap and kill nematodes. Between the two, post-infectional nematode resistance mechanism is well-suited for reducing nematode population densities from the soil for the successful production of nematode susceptible potato cultivars as successor crops in crop rotation systems.

Experimental system: Due to serious economic challenges posed by root-knot (Meloidogyne species) nematodes in sweet potato (Ipomoea batatas) production, the Sweet Potato Programme (SPP) of the Agricultural Research Council (ARC) in South Africa has since included screening for nematode host-status in its breeding-selection activities. Procedures: 20 sweet potato lines were screened against M. javanica, M. incognita race 2 and M. incognita race 4 in parallel trials inoculated with 3000 eggs and second-stage juveniles (J2) per established cutting. Results: At 56 days after inoculation, the reproductive potential (RP) of all test Meloidogyne species on sweet potato line 1990-10-2 was zero, whereas RP values on other lines were 19.48-342.7, 31.9-995.1 and 10.3-380.44 ranges for M. javanica, M. incognita race 2 and M. incognita race 4, respectively. Conclusion: Among the test sweet potato lines, line 1990-10-2 was non-host to populations of tropical Meloidogyne species in South Africa and could, therefore, be subjected to nematode resistance tests.

The withdrawal of highly effective synthetic chemical nematicides has left a void in management of plant parasitic nematodes in particular the root-knot nematodes. The objective of this study was to determine the host-status and host-sensitivity of potato cultivars 'BP1' and 'Buffelspoort' against Meloidogyne javanica and M. incognita race 2 under greenhouse conditions, with cultivar 'BP1' further tested under micro-plot conditions. Two separate studies were conducted under greenhouse conditions arranged in a randomized split- plot design with main plots being the cultivars and subplots being seven levels of nematodes, replicated six times and micro plot with seven treatments arranged in RCBD replicated eight times. Greenhouse studies: cultivars were inoculated with seven different nematode levels of M. javanica and M. incognita race 2. The reproductive factor values ( Rf) of greater than one were observed on both potato cultivars under the two Meloidogyne species. The final population ( Pf) of M. javanica on 'BP1' and 'Buffelspoort' was highly significant contributing 77 and 95% to the total treatment variation (TTV), respectively. The Rf contributed 9% to the TTV. Meloidogyne incognita race 2 significantly contributed 34 and 71% to the TTV in Rf and Pf, respectively, in 'Buffelspoort', whereas 38% contribution was recorded on 'BP1'. Under micro-plot conditions, the Rf for 'BP1' was highly significant contributing 63% to the TTV. Measured plant variables were not reduced under greenhouse conditions, however, plant height was significantly reduced by M. javanica under micro plot conditions for 'BP1'. In conclusion, the two potato cultivars were tolerant under greenhouse conditions and 'BP1' was susceptible to both tested Meloidogyne species under micro plot conditions.

Zucchini or squash (Cucumis pepo), also referred to as the green baby marrows, are highly susceptible to Meloidogyne species, without any genotype with resistance to the nematode genus. Cucurbitacin-containing phytonematicides are being used as alternatives to methyl bromide in various crops, with limited information on whether the product could induce auto-allelopathy in C. pepo cultivars. The objective of the study was to investigate the effects of Nemafric-BL phytonematicide on suppression of M. incognita and growth of zucchini under greenhouse conditions. Zucchini cv. ‘Cartesa’ seedlings were inoculated with 5000 eggs and second-stage juveniles (J2) of M. incognita and then managed at weekly basis using Nemafric-BL phytonematicide at 0, 2, 4, 8, 16 and 32%. Eight weeks after the treatments, relative to untreated control, the treatments reduced eggs (95–100%) and J2 (99–100) in roots, J2 (86–110%) in soil and final nematode population densities (97–100), but increased dry fruit mass (5–14%) and fruit number (66–137%), without affecting other plant variables. Nemafric-BL phytonematicide could be used in managing population densities of Meloidogyne species in zucchini production under greenhouse conditions without inducing phytotoxicity.

Increasing planting density/hole drip irrigation (HDI) could improve vegetative growth of indigenous leafy vegetables at the expense of nutrient elements due to intra-specific competition. The objective of the study was to determine the influence of planting density/HDI on selected immobile (Ca, Mg) and mobile (K, P) nutrient elements in wild cucumber ( Cucumis myriocarpus Naude.) indigenous leafy vegetable. A field trial was setup over two seasons using 0.6 m intra-hole drip tubes, with inter-row spacing at 1.0 m. Treatments were arranged in a randomised complete block design, with eight replications. At 56 days after transplanting, Ca, Mg, K and P in leaf tissues over planting density/HDI exhibited quadratic relations, with Ca and Mg each suggesting strong seasonality effects, which were not observed in K and P. Optimisation suggested that nine plants/HDI resulted in intensive intra-specific competition for the four nutrient elements. In conclusion, findings in the planting density of C. myriocarpus per HDI suggested some seasonal effects on Ca and Mg, without any such effects on K and P, with strong intra-specific competition, necessitating further empirically-based trials to establish the fertiliser requirements for C. myriocarpus in the proposed planting density system.

Attempts are underway to cultivate Moringa oleifera Lam. in tropical areas as a developmental crop due to its nutritional, pharmacological and industrial applications. However, the success of developmental-plant-related projects depends on the degree of nematode resistance in the introduced plants to the tropical root-knot (Meloidogyne species) nematodes. The objective of this study was to determine the degree of nematode resistance in M. oleifera seedlings to M. incognita race 2 and M. javanica under greenhouse conditions. Two parallel experiments were conducted, with seedlings in each inoculated with a series of different nematode species. At 56 days after inoculation, the M. incognita race 2 and M. javanica reproductive factor (RF) values ranged from 0–0.34 and 0.01–0.42, respectively. Nematode infection did not have any effect on plant growth variables. In conclusion, M. oleifera was resistant to population densities of tropical Moloidogyne species in South Africa.