Research Articles (Plant Production and Soil Science)

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A collection containing some of the full text peer-reviewed/ refereed articles published by researchers from the
Department of Plant Production and Soil Science

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    Does wind affect the orientation of vegetation stripes? A copula-based mixture model for axial and circular data
    (Wiley, 2025-07) Mingione, Marco; Lagona, Francesco; Nagar, Priyanka; Von Holtzhausen, Francois Victor; Bekker, Andriette, 1958-; Schoombie, Janine; Le Roux, Peter Christiaan
    Motivated by a case study of vegetation patterns, we introduce a mixture model with concomitant variables to examine the association between the orientation of vegetation stripes and wind direction. The proposal relies on a novel copula-based bivariate distribution for mixed axial and circular observations and provides a parsimonious and computationally tractable approach to examine the dependence of two environmental variables observed in a complex manifold. The findings suggest that dominant winds shape the orientation of vegetation stripes through a mechanism of neighboring plants providing wind shelter to downwind individuals.
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    High genetic diversity and limited regional population differentiation in populations of Calonectria pseudoreteaudii from Eucalyptus plantations
    (American Phytopathological Society, 2025-01) Li, WenWen; Liu, Feifei; Chen, ShuaiFei; Wingfield, Michael J.; Duong, Tuan A.
    Calonectria pseudoreteaudii causes a serious and widespread disease known as Calonectria leaf blight in Eucalyptus plantations of southern China. Little is known regarding the population biology or reproductive biology of this pathogen in the affected areas. The aims of this study were to investigate the genetic diversity, population structure, and reproductive mode of C. pseudoreteaudii from affected Eucalyptus plantations of southern China. Ten polymorphic simple sequence repeat markers were developed for the species and were used to genotype 311 isolates from eight populations. The mating types of all isolates were identified using the MAT gene primers. The results revealed a high level of genetic diversity of the pathogen in all investigated populations. Of the 90 multilocus genotypes detected, 10 were shared between at least two populations. With the exception of one population from HuiZhou, GuangDong (7HZ), the most dominant genotype was shared in the seven remaining populations. Discriminant analysis of principal components and population differentiation analyses showed that the 7HZ population was well differentiated from the others and that there was no significant differentiation between the remaining populations. Analysis of molecular variance suggested that most molecular variation was within populations (86%). Index of association analysis was consistent with a predominantly asexual life cycle for C. pseudoreteaudii in the studied regions. Although both mating types were detected in seven of the eight populations, the MAT1-1/MAT1-2 ratios in these populations deviated significantly from the 1:1 ratio expected in a randomly mating population.
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    Navigating power dynamics in food safety governance : the case of South Africa's compulsory specification for processed meat products
    (Institute for Social Development, University of the Western Cape, 2025-06) Mkhwanazi, Ntombizethu Simphiwe; Adelle, Camilla; Korsten, Lise
    The 2017–2018 listeriosis outbreak in South Africa had a severe impact on the processed meat industry, prompting significant regulatory changes including the development of the Compulsory Specification for Processed Meat Products (VC 9100). This regulation aimed to improve food safety standards by mandating the implementation of a Hazard Analysis and Critical Control Points system across all processed meat production facilities. Drafting of the VC 9100 was initiated in 2013 following concerns that existing voluntary standards were inadequate for protecting public health. However, progress was hindered by strong resistance from industry stakeholders who argued that compliance would be financially burdensome, particularly regarding the costs and levies associated with its enforcement. The listeriosis outbreak, which resulted in over 219 deaths, dramatically shifted the regulatory landscape. The crisis brought food safety to the forefront of the national agenda, compelling the government to accelerate the development and implementation of VC 9100. Despite the urgency, industry resistance persisted, with stakeholders lobbying for reduced levies and delaying the regulation's full enforcement. This case study highlights the complex interplay between public health priorities and industry interest in food safety governance. It also demonstrates how crises can serve as catalysts for regulatory change, with the listeriosis outbreak playing a pivotal role in overcoming industry resistance and advancing the implementation of essential food safety measures.
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    Extracts of southern African aquatic and wetland plant species as effective tyrosinase inhibitors
    (Elsevier, 2024-12) Lall, Namrita; Szuman, Karina; Madikizela, Bonani; Kok, Anna-Mari; De Canha, Marco Nuno; namrita.lall@up.ac.za
    South Africa harvests approximately 19 500 tonnes of medicinal plants annually for the treatment of various ailments and an additional 6000 tonnes is exported globally for the development and design of cosmetic and medicinal products. South Africa is home to 30 freshwater and marine ecological regions, however, medicinal plant species from these semi-aquatic and aquatic habitats are largely understudied in comparison to other biomes. The lack of knowledge and reported pharmacological activity of these species may be hindering the potential contribution to the herbal medicine and personal care markets. South Africa is Africa's largest market for cosmetic and personal care products and in 2018 this sector reported 3.2 billion US dollars in revenue. Eighteen (18) Southern African freshwater aquatic and wetland plant species were selected and screened for their potential as cosmeceutical ingredients by investigating their antibacterial, anti-tyrosinase and cytotoxicity. The extracts of Erythrina zeyheri and Plantago longissima exhibited antimycobaterial activity with MIC values of 125 µg/mL. Two extracts of the genus Cyperus, C. marginatus and C. sexangularis showed tyrosinase inhibition with IC50 values of 75.03 and 64.26 µg/mL, respectively. Carex rhodesiaca and Gunnera perpensa both exhibited dual antimicrobial activity against Cutibacterium acnes with MIC values of 250 and 125 µg/mL, respectively and anti-tyrosinase activity with IC50 values of 64.71 and 70.43 µg/mL. Persicaria senegalensis exhibited anti-tyrosinase activity with an IC50 of 71.59 µg/mL. Fractionation of P. senegalensis yielded F14 with an IC50 of 68.77 µg/mL against tyrosinase enzyme activity. Purification of F3 yielded (24S)-Stigmast-5,22(E)-dien-3-β-ol which is the first report of this compound from this species. This study provides scientific validation of the traditional use of the selected species and provides proof of concept for further investigations of these extracts as potential active ingredients in the personal care sector.
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    Evaluation of germination and early seedling growth of different grasses irrigated with treated mine water
    (MDPI, 2024-12) Mangwane, Mziwanda; Madakadze, Ignacio Casper; Nherera-Chokuda, Florence Veronica; Dube, Sikhalazo; Mndela, Mthunzi; Letsoalo, Ngoako; Tjelele, Tlou Julius; u14387027@tuks.co.za
    Coal mining is known to have negative impacts on the environment, necessitating land rehabilitation after mining activities. Amongst the problems associated with coal mining is the accumulation of acid mine drainage characterized by large amounts of heavy metals and high acidity. The impact of these environmental problems on the ecosystem around mining areas underscores a need to devise strategies that will ensure sustainable restoration of the ecosystem integrity to ensure environmental protection. Of these, treatment of acid mine drainage using calcium sulfate dihydrate, which is subsequently used for irrigation during phytoremediation, holds great promise for restoration of open-cast mines. However, although grasses are used for rehabilitation of coal mined areas, the impacts of treated mine water on the germination, seedling emergence, and plant growth of grasses are not well known. The aim of the study was to evaluate the germination and early seedling growth responses of different forage grasses to treated mine water. Seven forage grass species were selected, with four species represented by two varieties while others were represented by one variety, totaling 11 forage grasses. For each plant entry, 100 seeds were placed in J.R. Petri’s dishes lined with Whatman No. 2 filter paper and watered with distilled and mine water to assess germination. For the seedling establishment experiment, only five species were studied, in which twenty seeds per species were sown in pots containing mine soil and irrigated using distilled and treated mine water. The final germination percentage (FGP), germination rate index (GRI), corrected germination rate index (CGRI), and T50 were determined for the germination trail and total biomass was assessed for the seedling growth trail. The highest FGP for all grasses was attained under controlled conditions, using distilled water, ranging from 38–94%. All grasses germinated when watered using treated mine water and had a FGP ranging from 20–91%. Relative to distilled water, GRI and CGRI were highest only for L. multiflorum cv AgriBoost when seeds were watered using the treated mine water. All grasses watered with treated mine water produced high biomass for the first two weeks, after which biomass production started to decline. Two grasses, Eragrostis curvula cv Ermelo and Lolium multiflorum cv Archie, showed tolerance to treated mine water irrespective of its high electrical conductivity (557 mS∙m−1). Therefore, these grasses could be used in the rehabilitation of coal-mined areas irrigated with treated mine water.
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    Drivers of forest structure and biomass along a climatic gradient in the Soutpansberg, South Africa
    (Elsevier, 2025-09) Honold, Martin A.; Hilmers, Torben; Geldenhuys, Coert Johannes; Makhubele, Lucky; Van Tol, Johan J.; Ahmed, Shamim; Buys, Arno; Kotze, Elmarie; Tshidzumba, Ratsodo Phillip; Chirwa, Paxie W.; Tshaduli, Ndivhuwo; Araia, Mulugheta Ghebreslassie; Uhl, Enno; Pretzsch, Hans
    Forest structure plays a key role for providing different ecosystem services in rural regions worldwide. In forests and woodlands of southern Africa, there is a lack of quantitative information on prevailing structures, their abiotic and biotic drivers, as well as how stand characteristics will be affected by climate change. In this study, we established permanent research plots in mature developing stages of representative forests and woodlands occurring along a strong climatic gradient. Effects of site-available soil water and forest type were investigated for relevant dendrometric, as well as structural forest variables. We found site-available soil water having a significantly positive effect on all variables, apart from tree density and the ratio of multi-stem trees. Among the factors influencing site-available soil water, climate had a higher impact than topographical wetness index and soil available water capacity. Studied variables were also strongly influenced by the different forest and woodland types emerging, probably due to different species compositions, survival strategies and fire adaptations. Structural forest variables were revealed to have a positive effect on AGB especially in taller stands having enough space to form multiple canopy layers. In light of climate change with less soil water available and a related ongoing species and biome shift in southern Africa, our findings indicate that in the future, most of the studied forest variables, their related ecosystem functions and services are likely to decrease in the Soutpansberg region. The results of this study could be of use as input data for landscape level modelling, as well as for creating local management policies. HIGHLIGHTS • Forests and woodlands were investigated in a less studied region of South Africa. • Structural and dendrometric forest variables decreased with less water available. • Forest type played an important role apart from environmental drivers. • Structural heterogeneity showed a positive effect on AGB. • Climate change likely to reduce forest variables and related ecosystem functions.
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    Taking stock of South Africa's flora
    (Elsevier, 2025-09) Le Roux, M. Marianne; Klopper, Ronell Renett
    South Africa is rich in plant biodiversity and has a longstanding history of record-keeping of its plant resources. In recent years, updated versions of the South African National Plant Checklist (Checklist) have been published annually in electronic form, reflecting changes from published taxonomic revisions and new species descriptions. The most recent Checklist from 2025 recognises 23 514 taxa and 21 539 species (20 204 indigenous and 1 329 naturalised species). Of the indigenous species, 60.5 % are endemic to the country. The e-Flora of South Africa project (e-Flora) was initiated in 2013 and the first phase was completed in 2020. Both the Checklist and e-Flora data were published online in 2024 on the South African National Biodiversity Institute’s Biodiversity Advisor website. The e-Flora adds a layer of descriptive information to the list of names provided in the Checklist, thereby enhancing the utility of these outputs for end-users from a variety of biodiversity-related fields. The e-Flora is a dynamic data source with updates guided by changes incorporated in the Checklist. An overview of the statistics from both the Checklist and the e-Flora, as of March 2025, are provided. HIGHLIGHTS • The South African National Plant Checklist recognises 21,539 species. • Species endemism is recorded at 60.5 %. • KwaZulu-Natal hosts the most number of families and genera while the Western Cape is most speciose. • The e-Flora of South Africa holds descriptions for 22,056 taxa. • Checklist and e-Flora data are accessible on the SANBI Biodiversity Advisor.
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    Leaf anatomical traits of macadamia cultivars with potential links to drought tolerance
    (Elsevier, 2025-05) Maumela, Khodani; Taylor, Nicolette Jane; Oberlander, Kenneth Carl; Kritzinger, Angelique; angelique.kritzinger@up.ac.za
    Selecting Macadamia cultivars with anatomical traits capable of withstanding drought may improve water management in their cultivation. Macadamia integrifolia, Macadamia tetraphylla, and their hybrids are commercially grown in South Africa for their high-value edible nuts, however, to improve yields, irrigation is required. This study examined leaf and petiole anatomical traits linked with plant water-use strategies in four commonly planted cultivars: ‘695′, ‘814′, ‘816′, and ‘A4’. Key traits investigated included stomatal density, mesophyll thickness (palisade and spongy parenchyma), vein density, and petiole Huber value. Fully matured macadamia leaves with their petioles were collected from Komatipoort, Nelspruit, and KwaZulu-Natal South Coast during the spring flush of 2021 and the summer flush of 2022 for anatomical analysis. Box plots illustrated significant variations in leaf and petiole anatomical traits among macadamia cultivars and regions. Cultivars ‘814′ and ‘695′ exhibited higher stomatal densities and higher vein densities, while cultivar ‘814′ also showed thicker mesophyll tissues and higher petiole Huber values. These traits suggest that cultivars ‘814′ and ‘695′ may have improved water transport and potential drought tolerance than cultivars ‘816′ and ‘A4’. Seasonal variation accounted for 45 % of the observed variability in leaf and petiole anatomy, highlighting a strong influence of environmental factors during leaf development. However, the anatomical variation was shaped not only by environmental factors but also by cultivar-specific characteristics. These findings suggest that these leaf and petiole anatomical traits could serve as indicators of drought tolerance and help improve the water management practices in macadamia cultivation, particularly in regions with inadequate rainfall. HIGHLIGHTS • The water requirements of macadamia trees remain unexplored. • Leaf and petiole anatomy varies significantly across cultivars and regions. • Environmental conditions and genetic factors influenced leaf and petiole anatomy. • Selecting drought-tolerant cultivars improves the water management practices in macadamia cultivation.
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    Anti-acne and anti-hyperpigmentation potential of selected South African bryophytes with identification of oleamide as a lead compound
    (Elsevier, 2025-09) Paulsen, Alexander Quinn; Seaman, Jonathan Lloyd; Lall, Namrita; namrita.lall@up.ac.za
    Acne vulgaris (AV), a chronic dermal inflammatory condition, affects approximately 9.4 % of the global population, with adolescents exhibiting the highest prevalence. Cutibacterium acnes is a key pathogenic factor in this chronic inflammatory condition, often resulting in post-inflammatory hyperpigmentation (PIH), which is primarily treated with tyrosinase inhibitors targeting melanin synthesis. While bryophytes are underexplored in modern cosmeceutical research, they have a history of use in traditional Chinese and Indian medicine for skin ailments. This study aimed to evaluate the antibacterial and anti-tyrosinase potential of three bryophyte species—Bryum argenteum Hedw., Fabronia pilifera Hornsch., and Leptodictyum riparium (Hedw.) Warnst.—to assess their utility in managing AV and PIH. Ethanolic (70 % v/v) extracts were prepared from rinsed and unrinsed plant material. Antibacterial activity against C. acnes (ATCC 6919) was assessed via PrestoBlue microtiter plate assays to determine the minimum inhibitory concentration (MIC) of the bryophyte ethanolic extracts. Tyrosinase inhibition was measured using colorimetric microtiter plate assays to evaluate anti-hyperpigmentation potential. Lead extracts were further analysed for their volatile constituents using gas chromatography-mass spectrometry (GC-MS). Rinsed B. argenteum extract exhibited the strongest antibacterial activity with an MIC of 31.25 μg/mL, followed by rinsed F. pilifera extract at 62.5 μg/mL. All extracts showed minimal tyrosinase inhibition, with IC₅₀ values exceeding the highest concentration tested. GC-MS analysis identified oleamide, a compound with known antibacterial properties, as the major volatile constituent (17.37 %–52.64 %), with the highest concentration of oleamide found in rinsed B. argenteum extract. These findings suggest that selected bryophytes, particularly B. argenteum, may serve as promising sources of antibacterial agents for the treatment of AV. Although pharmaceutically significant tyrosinase inhibition was not observed, the high oleamide content warrants further investigation through bioassay-guided fractionation. This study introduces bryophytes as novel candidates for cosmeceutical applications targeting acne-related skin concerns. HIGHLIGHTS • Determination of antibacterial activity of selected bryophyte species. • Variation in bioactivity and chemical profile between bryophyte extract preparations. • Antibacterial (Cutibacterium acnes) activity of rinsed Bryum argenteum and Fabronia pilifera with MICs of 31.25 μg/mL and 62.5 μg/mL respectively. • Oleamide is the primary volatile constituent of 70 % ethanolic B. argenteum and F. pilifera extracts.
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    Adjuvant properties of selected medicinal plants for tuberculosis treatment
    (Elsevier, 2025-02) Kok, Anna-Mari; Meyer, Debra; Lall, Namrita; namrita.lall@up.ac.za
    Please read abstract in the article. HIGHLIGHTS • Many plant extracts with antimycobacterial activity have been identified recently. • Eucalyptus deglupta and Melianthus major had effective antioxidant capacity. • Searsia lancea showed significant hepatoprotection protection. • Increase in IL-12 by Eucalyptus deglupta and Sutherlandia frutescens.
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    A review of the world's response to COVID-19 and the potential of medicinal plants for future pandemics
    (Elsevier, 2025-09) Alston, Brandon James; Maphutha, Jacqueline; Ackron, Jessica; Kok, Anna-Mari; Lall, Namrita; namrita.lall@up.ac.za
    Coronavirus pandemics such as Spanish influenza, severe acute respiratory syndrome-coronavirus (SARS-CoV), middle east respiratory syndrome-coronavirus (MERS-CoV) and severe acute respiratory syndrome-coronavirus (SARS-CoV-2) have displayed high incidence and mortality rates prompting the need for repurposing of drugs, vaccine development and the investigation of medicinal plants. Research on previous coronaviruses has served as the foundation for COVID-19 (arising from SARS-CoV-2) research. Various medicinal plants such as Glycyrrhiza glabra, Ginkgo biloba, Curcuma longa and Artemisia annua have displayed favorable results against SARS-CoV-2. Medicinal plants as well as bioactive compounds derived from medicinal plants have been investigated in clinical trials to elucidate the effect on SARS-CoV-2. Several clinical trials evaluate the effect of the medicinal plant and bioactive compounds derived thereof on symptoms arising due to SARS-CoV-2 thus, the main aim of this review article is to highlight the gap in the investigation of the effect of medicinal plants and bioactive compounds on the specific mechanisms of COVID-19 in clinical trials. The review also highlights challenges pertaining to the standardization and quality control of medicinal plants as well as bioactive compounds derived from medicinal plants which may impede the feasibility of using medicinal plants in the clinical regimen for COVID-19 or future coronavirus pandemics. HIGHLIGHTS • SARS-CoV-2 is a highly infectious virus with high incidence and mortality rates. • Medicinal plants and bioactive compounds derived thereof are still relevant despite the use of repurposed antivirals (remdesivir) and vaccines. • Thorough clinical trials need to be conducted to elucidate the mechanism of action of medicinal plants and bioactive compounds derived thereof on COVID-19. • Gap in clinical trials leads to the use of unapproved medicinal plants and compounds which is a major health risk.
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    Spatio-temporal dynamics of Isoberlinia-dominated woodlands in disturbance-prone landscapes over 15 years
    (Elsevier, 2025-06) Idjigberou, Shegoun Eudes; Assede, Emeline Sessi Pelagie; Biaou, Severin; Gouwakinnou, Gerard Nounagnon; Natta, Armand Kuyema; Biaou, Samadori Sorotori Honore
    Understanding the impact of productivity and disturbance on vegetation succession is a crucial debate in community ecology, with significant implications for biodiversity conservation. Productivity and disturbance influence species richness and structure, enhancing our understanding of vegetation dynamics and species coexistence over time. Numerous theories, such as the Intermediate Stress Hypothesis, Intermediate Disturbance Hypothesis, and Dynamic Equilibrium Model, have been proposed to explain these mechanisms. However, our understanding of how productivity and disturbance affect the spatio-temporal dynamics of Isoberlinia-dominated woodlands remains limited. We analyzed floristic data from sixteen sites with 64 permanent plots (400 m² each) along a south-north precipitation gradient (1112–991 mm per year) over 15 years (2006–2020). We calculated species richness and density for sapling and adult trees, and estimated two main variables: potential productivity using water deficit as a proxy, and disturbance intensity using logging rate. A linear mixed effects model, with plots nested within sites as random variables, was developed to test the effect of potential productivity and level of disturbance on species richness and density, for sapling and adult trees. Our results showed that species richness (SR) and density, for saplings and adult trees decreased over time, regardless of the disturbance and potential productivity gradients. Compared to higher levels of disturbance, low and medium levels of disturbance significantly increase the species richness of saplings and adult trees. In addition, the density of adult trees and saplings decreased over time, but increased with the level of disturbance from high to low. These results suggest that increased disturbance reduces the density of woodland species in favor of invasive species, typically savanna species. Overall, our results are consistent with the Dynamic Equilibrium Model, highlighting the complex interactions between disturbance regimes, productivity gradients, and their effects on species richness within ecosystems. Efficient forest management in Isoberlinia-dominated would avoid the high levels of logging that promote the establishment of invasive species and would maintain the biodiversity of this ecosystem in the long term. HIGHLIGHTS • Examined how the productivity and disturbance affect the spatio-temporal dynamics of Isoberlinia-dominated woodlands. • Analyzed data from 64 permanent plots along a south-north precipitation gradient over 15 years. • Species richness and density for saplings and adult trees decreased over time. • Low to medium disturbance levels increase the richness of saplings and adult trees compared to higher levels. • Increased disturbance favored invasive savannah species over woodland species.
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    A third biodiversity metric in the third pole
    (Wiley, 2025-04) Oberlander, Kenneth Carl; kenneth.oberlander@up.ac.za
    The readers of this journal need no introduction to the threat posed to biodiversity by anthropogenic factors such as habitat degradation and climate change. The (sometimes considerable) efforts by many national governments to increase biodiversity protection over the last few decades, via the establishment of protected areas for conservation, have nevertheless met with criticism, particularly with regard to the evidence base used for the establishment and expansion of such protected areas (Maxwell et al. 2020). This is particularly acute for regional planning efforts involving multiple governments, where the effects of national borders on biodiversity conservation may have profound consequences in the near future (Li et al. 2025). Ideally, such decisions should be made taking into account evidence from multiple different levels of biological organisation, but this is seldom achieved in reality.
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    Effect of storage conditions on soybean seed quality produced by smallholder farmers within two districts of Gauteng, South Africa
    (University of Kassel, 2024) Mahlangu, A. Zanele; Truter, Mariette; Kritzinger, Quenton; zanele.mahlangu@up.ac.za
    Seed quality comprises of physical, physiological, and health attributes. Moreover, significant aspects of seed quality include seed viability and vigour. Maintaining good seed quality under sub-optimal storage conditions is one of the major challenges smallholder soybean farmers face. Hence, this study aimed to determine the effect of on-farm storage conditions on the seed quality of soybeans from smallholder farmers within the Gauteng Province, South Africa. The objectives of this study were to i) evaluate and compare the viability and vigour of farm-saved soybean seeds, and ii) evaluate the effect of seed moisture and simulated storage period on the rate of deterioration of the seeds. Farm-saved seed samples collected from the twenty-two smallholder farmers from two districts within the Gauteng Province showed significant variations in terms of seed moisture, viability, vigour [accelerated aging (Aa) and conductivity], and in the rate of deterioration. The seed moisture content ranged from 7.8-30.8 %. The majority of the farm-saved seed samples had a germination percentage significantly higher than 75 %, irrespective of the storage conditions. On the other hand, seeds subjected to Aa and to the controlled deterioration test resulted in less vigourous seedlings. Seeds that were subjected to 24 hr Aa had a significantly (p < 0.05) higher germination than those subjected to 72 hr Aa. The 72 hr Aa results verified the reduction of seed vigour as the storage period increased. A similar declining germination trend was observed on seeds subjected to deterioration tests under high moisture content levels. The study gives an indication of how the sub-optimal storage facilities used by smallholder soybean farmers affect seed quality. Based on the vigour tests, it can be assumed that storing seeds with high SMC under high relative humidity coupled together with high temperatures for prolonged periods tends to deteriorate the seeds rapidly and thus reduce seed vigour.
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    Biotic pressure outweighs the influence of resource availability on physical defence investment in a tropical tree
    (Oxford University Press, 2025-06) Babah Daouda, Bio Barriou; Kouagou, M'Mouyohoun; Assede, Emeline Sessi Pelagie; Gaoue, Orou G.
    Plants have long-lasting and complex interactions with herbivores, including insects and mammals. In response to high herbivory rates, plants either tolerate biomass loss or develop several defence mechanisms, such as physical defence. The resource availability hypothesis (RAH) predicts that plant defence investment is dependent on resource availability and plant's life history. However, the effect of resource availability on plant investment in defence is mediated through biotic pressure. We tested the effects of soil qualities and browsing pressure on the physical defence and reproductive investments in Acacia sieberiana at the Pendjari Biosphere Reserve in West Africa. We selected six populations, including three in the Pendjari River floodplain where soil moisture is high but with high elephant browsing pressure, and three populations on the plateau in the hunting zone where soils are drier and relatively poorer with a lower density of elephants. We found greater investment in physical defence for trees in the floodplain. Furthermore, A. sieberiana trees produced less fruit in the floodplain than in the plateau. Contrary to the predictions of the RAH, we found more and longer thorns in populations in the richer floodplains than on the plateau. This was linked to higher elephant browsing pressure in the floodplains. This physical defence was probably induced to cope with the episodic but high levels of herbivory observed in this environment. Surprisingly, the negative influence of thorn number and size on the likelihood of elephant damage was observed only in the rich floodplains and not in plateau sites. Altogether, our study demonstrates that the influence of resource availability (soil moisture, pH, and fertility) in shaping plant physical defence can be outweighed by high herbivory pressure.
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    Bark investment is key to forest expansion into African savannas by conferring resistance to fire and seasonal drought
    (Oxford University Press, 2025-05) Rosell, Julieta A.; Vetter, Susanne; Olson, Mark E.; Greve, Michelle
    BACKGROUND AND AIMS : Forest expansion into savannas is widespread even though fire and seasonal drought provide environmental conditions against encroachment by forest specialists. A distinct suite of species can establish under savanna trees, forming bush clumps and facilitating forest establishment. Understanding the functional traits of clump-forming species is crucial for uncovering encroachment mechanisms and devising management strategies. Bark likely plays a key role in enabling clump initiation. Fire resistance can be achieved by accumulation of outer bark thickness (OBT), height and/or stem diameter (SD), while drought resistance may be enhanced by greater inner bark thickness (IBT), associated with water and carbohydrate storage. METHODS : We selected representative savanna, clump-forming and closed-canopy species (ecological categories) at two South African sites experiencing forest expansion and differing in rainfall and fire frequency. We compared OBT–SD and IBT–SD allometries across ecological categories and sites and examined whether categories separated along axes reflecting fire/drought resistance (OBT and IBT) and resource allocation strategy (density and water content, leaf size). KEY RESULTS : OBT–SD scaling of clump-forming species was more similar to savanna than forest species, and savanna species at the more fire-prone savanna had steeper OBT–SD scaling, consistent with high OBT providing fire protection in early clump formation. Similar IBT–SD slope across groups was consistent with similar metabolic needs, while higher intercepts in savanna and clump-forming species indicated higher water storage. ‘Cheap’ low-density tissues in savanna species allow fast accumulation of SD and OBT and resistance to fire topkill. Closed-canopy species had denser tissues and thin stems and bark for a given height, while the clump-forming species were intermediate. CONCLUSIONS : Bark and probably other traits are key in the capacity of some species to form bush clumps. Identifying these traits and the mechanisms underlying clump formation is essential for managing encroached savannas and grasslands.
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    Assessing the use of remotely sensed surface water flux to estimate net groundwater storage change in an aquifer predominantly used for irrigation
    (Elsevier, 2025-07) Viviers, Cindy; Van der Laan, Michael
    Please read abstract in the article.
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    Assessing extensive pasture-based beef production in South Africa under future climate change conditions
    (Elsevier, 2025-10) Magona, Christopher; Hassen, Abubeker; Tesfamariam, Eyob Habte; Mengistu, Michael; Visser, Carina; Oosting, Simon; Van der Linden, Aart; carina.visser@up.ac.za
    CONTEXT : Assessing the impact of climate change on extensive pasture-based beef production across varied agro-ecological regions is crucial for designing customized adaptation measures. OBJECTIVE : This study assesses the effects of climate change on extensive pasture-based beef production systems in three South African agro-ecological regions (Bloemfontein, Phalaborwa and Buffalo Berlin) under two climate change scenarios, namely the representative concentration pathways (RCPs) 4.5 and 8.5. METHODS : The LiGAPS-Beef model, previously calibrated for the region, was used to evaluate the impact of climate change on beef cattle production under pasture-based extensive systems. Four breed types, namely Bos taurus, Composite, Zebu indicine and Sanga cattle were included in this study. Genetic parameters for each breed were obtained from SA Stud Book, Livestock Registering Federation (LRF) and literature. Measured historical weather data was obtained from the South African Weather Service for the three agro-ecological regions. An ensemble of eight regional climate model (RCA4) simulations from the CORDEX Africa initiative was used to generate future climate change projection data for the period 2036–2065 under RCP 4.5 and RCP 8.5 scenarios. The future nutritional composition data for forage was collected from studies that simulated and predicted future forage quality under climate change conditions. RESULTS AND CONCLUSION : The study found that the baseline average daily gain (ADG) was significantly higher (0.40 kg/head/day) than the simulated RCP 4.5 (0.21 kg/head/day, −48 %) and RCP 8.5 (0.20 kg/head/day, −51 %) ADGs regardless of breed type when both feed quality and feed quantity limited growth. Although the effect of the climate change scenarios on beef production was agro-ecological region dependent, the performance of Bos taurus declined more than other breeds under future climate scenarios while the Sanga and the Composite types were the most resilient, especially in hot climate areas. Model simulations predict that future climate change will have a greater negative impact on cattle in Buffalo Berlin and Phalaborwa, while those in Bloemfontein will be least affected. The study also highlights that under future climate change scenarios, pasture quality will be the key factor influencing cattle growth in Bloemfontein and Buffalo Berlin, while pasture quantity will be the dominant factor in Phalaborwa if stocking rates remain unchanged. The study highlights the need for nutritional and pasture management interventions for pasture-based extensive system (e.g., feed supplementation, adjusting the stocking rate to match pasture availability, identifying and integrating drought and/or heat tolerant ecotypes, fodder trees that provide shade for the animals) to mitigate the expected decline in beef cattle performance in South African agro-ecological regions. SIGNIFICANCE : Quantifying the impact of anticipated climate change on pasture-based extensive beef production and identifying specific factors that limit beef production per breed type in the different agro-ecological regions is crucial for assessing the potential ramifications on beef production. This information empowers farmers and policy makers to develop targeted mitigation and adaptation strategies that promote resilience of the beef production system in the respective regions. HIGHLIGHTS • Quantifying climate change impact on beef production is vital for coping measures. • Beef cattle growth was simulated under RCP 4.5 and RCP 8.5 in South Africa. • 2050 simulated growth declined by 48 % in RCP 4.5 and 51 % in RCP 8.5 from baseline. • Growth of Bos taurus was most adversely affected, but Sanga was the most resilient. • Location-specific intervention is vital to sustain beef production in South Africa.
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    Proposals to conserve the name Aloe mitriformis with a conserved type and the name A. microstigma against A. perfoliata (Asphodelaceae: Alooideae)
    (Wiley, 2025-06) Klopper, Ronell Renett; Smith, Gideon F.; Van Wyk, Abraham Erasmus (Braam)
    No abstract available.
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    In vitro antiplasmodial activity and cytotoxicity of three Ziziphus (Rhamnaceae) species from South Africa
    (Elsevier, 2025-06) Mabuza, Mcebisi Junior; Kaiser, M.; Tshikalange, T.E.; Yusuf, Abdullahi Ahmed; Bapela, Mahwahwatse Johanna
    Please read abstract in the article.