Volume 5 Special Issue 1 2011
Botswana Plant Research

How to reference: Mukanganyama S, Ntumy AN, Maher F, Muzila M, Andrae-Marobela K (2011)Screening for Anti-infective Properties of Selected Medicinal Plants from Botswana. In: Botswana Plant Research. The African Journal of Plant Science and Biotechnology 5 (Special Issue 1), 1-7

Guest Editor

Tabo Mubyana-John

Dept of Biological Sciences, University of Botswana, Botswana

/www.ub.bw/

CONTENTS AND ABSTRACTS

Stanley Mukanganyama (Zimbabwe), Aku N. Ntumy, Fozia Maher, Mbaki Muzila, Kerstin Andrae-Marobela (Botswana) Screening for Anti-infective Properties of Selected Medicinal Plants from Botswana (pp 1-7)

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Original Research Paper: Thirty nine ethanol extracts from 26 plants widely distributed in Botswana were screened for antimicrobial activities against three Gram-positive, two Gram-negative bacterial strains, two Candida species and one Mycobacterium species. Screening was carried out at an initial concentration of 500 µg/disc using the disc agar diffusion method. Most of the plant species gave rise to antifungal activities (20/24), some of them specifically, such as Acrotome inflata, Bridelia mollis, Dichrostachys cinerea, Dicerocaryum eriocarpum, Dicoma capensis, Gomphrena celosioides, Tagetes minuta and Waltheria indica. Minimal inhibitory concentrations (MICs) of extracts with inhibitory activities against Candida albicans, a major opportunistic infective agent in immunocompromised patients, varied between 0.039 and 2.5 mg/ml. Extracts of 10 plant species inhibited the growth of Mycobacterium aurum, a non-pathogenic model organism with similar drug susceptibility as Mycobacterium tuberculosis. MIC values of anti-mycobacterial extracts ranged from 0.039 to 2.5 mg/ml. Interestingly, Ocimum canum leaf extracts and Elephantorrhiza burkei root extracts displayed the lowest MICs against both HIV/AIDS opportunistic pathogens with values of 0.039 mg/ml against Mycobacterium aurum, and MIC values of 0.039 and 0.078 mg/ml against Candida albicans, respectively. Extracts of two plant species, Elephantorrhiza elephantina and Persiceria limbata, exhibited antimicrobial properties against all eight microorganisms tested and only these two extracts were active against the Gram-negative Escherichia coli strain. Antimicrobial ethanol extracts with the lowest MIC values did not show acute in-vitro cytotoxicity up to a concentration of 1000 µg/ml using human embryonic kidney cells (HEK293). The findings confirm some anti-infective and wound healing ethnomedical uses in Botswana and show the potential to develop antimicrobial preparations from community natural resources.

Sarah Kizza (Uganda) Herbaceous and Woody Plant Properties in Abandoned Kraal Areas in a Hardveld Botswana (pp 8-15)

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Original Research Paper: Herbaceous and woody plant species in abandoned traditional kraals were investigated. To achieve the aim of this study, nutrient status of soil in addition to vegetation composition and communities from the kraal sites were analyzed and results compared with those from control sites. A total of 25 kraals that had been abandoned between 5 and 45 years were sampled. Data were analyzed using multivariate procedures; a two-way indicator species analysis (TWINSPAN), detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) to establish classification of the plant communities. The significant environmental variables identified with t-values above 2.1 that determined the composition and patterns of the plant communities were organic matter, plant available nitrogen, calcium and moisture content. The results show major differences in soil physio-chemical properties and also in patterns and composition of vegetation communities between kraals and their surrounding areas. Evidence from the results show that kraal areas play an important role in determining key resource areas by influencing systematic distribution of nutrients. With kraals tending to increase the heterogeneity in the natural distribution of nutrients, it is apparent that animal waste deposited in the kraals modify vegetation patterns as high nutrient tolerant species gain competitive advantage over those that are not. The findings provide some important information that could explain herbaceous and woody species community patterns particularly in semi-arid environments where livestock management by the use of traditional kraals is a common practice.

Michael Murray-Hudson, Gagoitseope Mmopelwa (Botswana) Biomass Production and Economic Value of Phragmites australis Reedbeds in the Southern Okavango Delta, Botswana (pp 16-20)

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Original Research Paper: Most work globally on Phragmites spp. has been done in temperate northern hemisphere localities, where winter low temperatures and short day lengths cause a seasonal decrease in growth. In this study, we report above-ground stem length-mass relationships, stem densities and daily growth rates in 3 Phragmites australis reedbeds in the flood-pulsed, subtropical Okavango Delta, with the aim of assessing the economic value of this plant, which is widely used throughout north-western Botswana for cladding house walls and fencing yards. Stem density averaged 77 m^-2 in 32 plots. Length-mass relationships were best represented by a power function y = 8.05x^1.85, where y is the dry mass in grams, and x is the length in metres (r² = 0.895). The mean daily growth rate was 0.015 m and did not appear to vary systematically with season. The maximum standing crop calculated from stem length was 2.89 kg m^-2, and occurred in May 2005. Annual above-ground production was conservatively estimated at 20-30 t ha^-1. Assuming that harvesting takes place not more than once annually, reed beds in the Okavango Delta are worth ~US$ 45,000 ha^-1 at market. This land use value is over 90 times that of flood recession agriculture in the same area.

Bakang Baloi, Maitshwarelo Ignatius Matsheka, Berhanu Abegaz Gashe (Botswana) Isolation of Cultivable Halophilic Bacillus sp. from the Makgadikgadi Salt Pans in Botswana (pp 21-25)

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Original Research Paper: Halophilic bacteria from the Makgadikgadi salt pans in north central Botswana were isolated using culture-dependent methods. Polymerase chain reaction (PCR) amplification of the 16S rRNA gene and phylogenetic analysis were used to identify the strains. Culturing was done aerobically in six different complex salt media. Salt concentrations used were 15, 20, 25 and 30% (2.6, 3.4, 4.3 and 5.1 M, respectively) NaCl, at pH 7.2 to pH 8.0. Four colony morphology types were isolated in axenic cultures comprising Gram-positive cells. Universal bacterial primers were used to amplify 16S rDNA from chromosomal DNA isolated from three of the four distinct colony groups. Restriction enzyme digests analysis of the 16S rDNA revealed seven RFLP types. Five of the RFLP types were subjected to sequencing. Comparison of the 16S rDNA sequence alignment to reference sequence data bases showed samples S2012A3, S2012B2 and S2012B3 to have between 95 and 99% homology to Bacillus sp.BH 164 and Bacillus sp.HS 136^T, a novel species recently described as Bacillus persepolensis. Isolate S4102D4 showed 95 to 99% homology to Thalassobacillus sp. JY0201 and Thalassobacillus sp. FIB228 and Halobacillus sp. MO56 species. All five isolates had at least 95% similarity to published sequences implying they could be species within the described genera. A sub-tree drawn to compare the isolates indicated two phyletic lines with S4102D4 being an outlying strain and S2012A3, S2012B2 and S2012B3 being a closely related clonal group all of which branch from Bacillus sp.BH 164. Pending conclusive culture, biochemical and polar lipid composition data these microorganisms are regarded as previously un-described and therefore novel species of halophilic bacteria.

Tuduetso Motlalepula Mokgatlhe (Botswana), Anthony Bupe Siame (Canada), Joanne Elizabeth Taylor (UK) Fungi and Fusarium Mycotoxins Associated with Maize (Zea mays) and Sorghum (Sorghum bicolor) in Botswana (pp 26-32)

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Original Research Paper: The mycoflora and Fusarium mycotoxins, zearalenone and fumonisin B₁, associated with 100 samples of maize and sorghum grains and meals sold in Gaborone (Botswana) were determined. Fungal contamination was greatest on sorghum grains (96%) and least on white maize grains (77%). Maize and sorghum meals had a fungal contamination of 2.5 ´ 10³ CFU/g and 2.3 ´ 10³ CFU/g, respectively. The predominant genera isolated from the grains and meals were Aspergillus, Fusarium, and Penicillium. Other genera included Alternaria, Nigrospora, Acremonium and Phoma. Fusarium verticillioides was the most prevalent Fusarium species, accounting for 76% of all the Fusarium isolates. Other Fusarium species were F. proliferatum, F. semitectum and F. subglutinans. The presence of these fungi in food commodities may lead to food deterioration, and mycotoxin contamination. Nine isolates of Fusarium belonging to the four species were tested for their ability to produce fumonisin B₁ on autoclaved maize and sorghum substrates. The amount of fumonisin B₁ produced ranged between 1,700-789,000 µg/kg. The collected samples were also analyzed for the presence of zearalenone and fumonisin B₁ using thin layer chromatography and high-performance liquid chromatography. Contamination with zearalenone and fumonisin B₁ was 97% and 49%, respectively. The amount of zearalenone and fumonisin B₁ ranged from 3-980 µg/kg and from 9-2183 µg/kg, respectively. Five samples had concentrations exceeding 1000 µg/kg. The presence of mycotoxins indicates a need to set up standards that regulate their levels in maize and sorghum sold in Botswana.

Tabo Mubyana-John, Mareledi G. Wright (Botswana) Fungi and their Use in the Possible Control of Nematodes in Botswana Soils (pp 33-40)

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Original Research Paper: A study assessing fungi isolated from three climatic regions of Botswana as a possible control for root knot nematodes(Meloidogyne spp.)affecting the tomato (Lycopersicon esculentum L. var. ‘Money maker’) crops was conducted. Out of 1,250 soil fungal isolates, only 232 soil fungi from the Okavango Delta, Bobirwa district and different saltpans in Botswana could be sub cultured, and screened for antagonism against Meloidogyne sp. Seven of the isolates i.e., Trichoderma sp., Penicillium sp., Dendriphiopsis sp., Fusarium chlamydosporium, Cochliobolus sativus, Aspergillus fumigatus and an unidentified sterile fungus showed potential to immobilize nematode juveniles on agar plates within 2-4 days. C. sativus and Dendriphiopsis sp. showed maximum paralysis on agar plates and eventually death of the Meloidogyne sp. juveniles. In greenhouse studies using tomato plants the fungi alleviated the effect of nematodes by increasing plant, shoot height and root weight as compared to the reference controls. Cochliobolus sativus and Trichoderma sp. showed maximum plant protection of tomato plants under greenhouse conditions. Fungi ability to produce cellulase and chitinase were some of the mechanisms studied. The results indicated that Trichoderma sp., Penicillium sp., Dendriphiopsis sp., Fusarium chlamydosporium, Cochliobolus sativus, and Aspergillus fumigatus are nematode antagonistic fungi indigenous to Botswana that can be used to control nematodes as they are better adapted in comparison to introduced fungi.

Olusegun Areola, Oagile Dikinya, Larona Mosime (Botswana) Comparative Effects of Secondary Treated Waste Water Irrigation on Soil Quality Parameters under Different Crop Types (pp 41-55)

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Original Research Paper: This study compares soil quality parameters, and salinity and heavy metal levels in soils cultivated with different crops under secondary treated wastewater irrigation in the Glen Valley, near Gaborone City, Botswana. The hypothesis being tested is that the impact of the wastewater on soil quality varies with soils and crop types. The study covers 4 selected crops, maize (Zea mays L.), spinach (Spinacia oleracea), olive(Olea europaea), and tomato (Solanum lycopersicum), most widely cultivated by the farmers. Three farm plots per crop type were sampled at 5 sampling points and at two soil depths, 0-15 and 15-30 cm. Samples were also collected at 5 sampling points from two control sites. Irrigation water samples were collected for microbiological analysis from 2 farms per crop type. The most significant differences and relationships are between those crop farms, such as maize and two of the spinach plots, with predominantly sandy soils (loamy sands - sand loams) on the one hand; and the olive, tomato and one of the spinach plots with sandy clay loams on the other. The importance of soil texture was confirmed by the strong correlations between the sand and silt contents, several soil quality parameters, heavy metals and other elements. With the exception of Cd and Hg, most soil heavy metal contents were lower on the irrigated plots than on the control plot. The EC values also show that soil salinity levels were still low on the irrigated fields, but SAR and ESP values were high. The secondary treated wastewater being used in the Glen Valley is biologically clean, but one recorded case of E. coli emphasizes the importance of avoiding sprinkler irrigation at all costs to protect human health.

Agripina Banda, Tabo Mubyana-John, Joanne E. Taylor (Botswana) The Influence of Range Fire on Soil Fungi, Microbial Activity and Soil Properties along the Boro Route of the Okavango Delta (pp 56-62)

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Original Research Paper: The influence of burning on soil microbial dehydrogenase activity, nitrogen content and fungal population along the Boro route in the Okavango Delta was assessed in the flood and dry seasons. Soil samples from the burnt plots and the adjacent control un-burnt plots were cultured on agar plates using dilution methods.Fusarium spp. were dominant while Aspergillus species were low in burnt plots. The other fungi such as Drechslera sp., Exophiala jeanselmmei, Penicillium compactum and Chrysosporium merdarium were only in the burnt plots as compared to unburnt control plots. However, fungal diversity and soil dehydrogenase activity reduced after 6 months of burning showing significant increase in Chrysosporium merdarium in almost all the burnt plots. The influence of burning on soil nitrogen was insignificant instead flooding had a stronger influence on nitrogen content than burning. The results indicate that burning increased fungal diversity and biomass, however reduces overall microbial enzyme activity after burning without influencing soil nitrogen and pH.

Samson Kabajan Kenneth Kaunda, Kefilwe Matlhaku, Mmilili Myles Mapolelo, Johannes Mokgosi (Botswana) Shoot Production by Acacia tortilis under Different Browsing Regimes in South-East Botswana (pp 63-68)

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Original Research Paper: We investigated shoot production by Acacia tortilis under three distinct land-use types and browsing regimes in south-eastern Botswana: a large mammal exclosure (UB Nature Reserve, UBNR), a conservation area (Gaborone Game Reserve, GGR), and a livestock area (Tlokweng Rangelands, TR). We applied one-way ANOVA to determine variation in shoot production within and amongst land-use types, and also across vertical browsing levels (“Low”, “Medium” and “Upper”). Mean shoot length varied significantly amongst the three habitats, being highest in GGR, TR, and lowest in UBNR. Spinescence (spine number and mass) differed significantly under the three land-use types, being highest in GGR, TR, and UBNR, respectively. Within land-use types, shoot length differed significantly between the three browsing levels. Shoot length declined from the “Upper” to the “Low” browsing levels or zones. Leaf dry-mass differed significantly between the three browsing levels, decreasing from the highest to the lowest levels. The highest number of thorns produced was significantly higher on the “Upper” browsing zones. Thorn mass did not vary significantly across the browsing zones. We postulate that differential browsing pressure elicited the variable response in shoot production across the three land-use categories, and further discuss the implications for wildlife and rangeland management.

Moffat P. Setshogo, Collen M. Mbereki (Botswana) Floristic Diversity and Uses of Medicinal Plants Sold by Street Vendors in Gaborone, Botswana (pp 69-74)

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Original Research Paper: The sale of herbal medicine, either as concoctions or single plant specimens, has become common in the streets and main shopping centres of major towns and cities in Botswana. A study was undertaken to collect information on the uses of medicinal plants sold by street vendors in Gaborone, Botswana, during June 2008 to December 2008. The indigenous knowledge of the street vendors and the plants used for medicinal purposes were collected through questionnaire and personal interviews during field trips. The survey showed that the street vendors used 47 species of plants distributed in 45 genera belonging to 29 families to treat various diseases and health conditions. The documented medicinal plants were mostly used to cure skin sores, sexually transmitted diseases (STD) and asthma. In this study, the most dominant families are the Asteraceae and Fabaceae, each with 5 species and roots were most frequently used for the treatment of diseases accounting for 62% of the medicines sold. This study showed that many people in Botswana still continue to depend on medicinal plants for primary healthcare.

Mbaki Muzila, Moffat P. Setshogo, Baleseng Moseki, Rachel Morapedi (Botswana) An Assessment of Prosopis L. inthe Bokspits Area, South-Western Botswana, Based onMorphology (pp 75-80)

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Original Research Paper: The genus Prosopis comprises 44 species. Extensive introgression and hybridization is suspected in the genus, which makes identification of the species very difficult. Accurate identification of the species is crucial in controlling invasive species, within this genus. That is so because the method of control is species specific. The objective of the study was to determine the taxonomic structure of Prosopis species in Southern Botswana. A systematic qualitative approach was used to sample the species such that specimen selection was based on observable morphological discontinuities. The morphological characters were subjected to multivariate analysis since the analysis has been reported to be good at identifying hybrids. The multivariate analysis included anova, cluster analysis, factor analysis and canonical correlation. The study revealed four pure lines of Prosopis and nine hybrid species. The pure lines are Prosopis chilensis, P. juliflora, P. velutina and P. glandulosa and they all belong to one section, ALGAROBIA. The observed hybrids were P. chilensis x P. glandulosa, P. glandulosa x P. chilensis, P. juliflora x P. glandulosa, P. chilensis x P. juliflora, Acacia karroo x P. juliflora, P. glandulosa x P. pallida, P. juliflora x P. pallida, P. chilensis x P. juliflora x P. glandulosa and P. chilensis x P. pallida. It was therefore concluded that the Prosopis speciesin Southern Botswana have formed a hybrid swam. And for the hybrids P. chilensis x P. glandulosa and P. glandulosa x P. chilensis it was concluded that gene flow between P. chilensis and P. glandulosa is bidirectional. For the hybrid P. juliflora x P. glandulosa it was concluded that gene flow was from P. juliflora to P. glandulosa.

Samuel Adelabu, Olusegun Areola, Reuben J. Sebego (Botswana) Assessing Growing Season Changes in Southern Botswana (pp 81-88)

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Original Research Paper: Perfect timing of planting date is not only one of the key factors which strongly affect crop production in rain-fed agriculture but it is also a valuable leading indicator for food security monitoring in semi-arid environments like Botswana. This is especially true when, as in many parts of semi-arid regions, the rainy season starts with some light showers followed by dry spells, which can cause poor crop emergence or even desiccate a young crop and lead to poor yields and greater food insecurity and hunger. Unfortunately, such information on appropriate planting dates is rarely available from ground sources in a timely manner. However, operational remote sensing products such as vegetation index can be used to complement ground sources and hence fill missing gaps in planting date forecasting and monitoring. The aim of this study therefore was firstly to derive the growing season metrics for the southern district of Botswana using standard methods of deriving growing season from climatic indices and from satellite imagery and secondly to study the trend of the growing season metrics in the study area. The results from the two approaches showed that the onset and cessation of growing season had shifted backwards in both cases. Onset dates had shifted from the initial mid-September in the early 1960s to early November as of 2009 while cessation dates had shifted from early April to late January. Consequently, the growing season had contracted in length by an average of 14 decadal from the initial value of 22 decadal in the early 1960s. The study also showed no statistically significant difference between the growing season metrics derived from the two approaches (climatic and NDVI) hence any of the two approaches can be used to determine growing season metrics in the study area.

Baleseng Moseki, Kebonyethata Dintwe (Botswana) Characteristics of Two Sorghum Cultivars Subjected to Water Stress (pp 89-91)

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Research Note: The effects of water stress on the photosynthetic characteristics of two locally-cultivated sorghum cultivars (‘Segaolane’ and ‘Town’) were investigated over a period of weeks. Water stress was imposed on 1-week-old plants by withholding water. Measurements of chlorophyll fluorescence were used to determine changes in the efficiency of light utilization for electron transport, the occurrence of photoinhibition of photosystem II photochemistry on the sorghum cultivars. Drought treatment significantly decreased leaf area in all species, an important factor in drought-induced decreases in photosynthetic productivity. Water-stressed ‘Town’ exhibited a decrease in maximum photochemical efficiency of PSII (estimated from dark-adapted F_v/F_m ratio) with increasing period of withholding water. Light-adapted F_v’/F_m’ estimated the efficiency of excitation energy transfer to open PSII centres. Water-stressed ‘Town’ displayed a decrease in the efficiency of excitation energy transfer to open PSII reaction centres throughout the entire study period. The quantum yield of PSII electron transport (ΦPSII), which represents electron flow beyond PSII, decreased markedly in water-stressed ‘Town’ compared with that of water-stressed ‘Segaolane’. These initial findings indicate that ‘Town’ is more prone to photoinhibition than ‘Segaolane’.