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Mabhaudhi T.,University of KwaZulu - Natal | Modi A.T.,University of KwaZulu - Natal | Beletse Y.G.,Vegetable and Ornamental Plant Institute VOPI
Acta Horticulturae | Year: 2013

No information is available on responses of South African taro landraces to water stress. The objective of this study was to evaluate the responses, and mechanisms thereof, of taro to water stress under controlled and field conditions. Taro landraces were collected from rural areas in KwaZulu-Natal, South Africa. A pot trial was planted in tunnels at the University of KwaZulu-Natal with two factors: three landraces and water stress (NS - no stress, IS - intermittent stress and TS -terminal stress), replicated six times. For NS, soil water content (SWC) was maintained at 75% field capacity (FC). IS involved watering pots to 75% FC during crop establishment, and allowing SWC to deplete to 30% FC during the vegetative stage, before returning to 75% until harvest maturity. For TS, SWC was maintained at 30% FC for the entire growing period. Field trials were planted in October 2010, with irrigation (full irrigation versus rainfed) as a main factor and landrace type as sub-factor, replicated three times. SWC was monitored weekly. Emergence, plant height, leaf number, leaf area, LAI, vegetative growth index (VGI) and stomatal conductance (SC) were determined weekly. Results from both pot and field trials showed that taro landraces were slow to emerge (∼49 days). There were significant differences (P<0.001) between landraces with respect to final emergence. Taro growth (plant height, leaf number and leaf area), for both trials, was shown to be significantly (P<0.05) reduced by water stress. Under field conditions, SC, LAI and VGI were significantly (P<0.05) lower under rainfed conditions compared with irrigated conditions. It is concluded that emergence and vegetative growth parameters of KwaZulu-Natal taro landraces are sensitive to water stress. Data from this study will be used to calibrate AquaCrop and presented as a possible option to manage taro under dryland and irrigated conditions in the warm subtropical areas of South Africa.


Mabhaudhi T.,University of KwaZulu - Natal | Modi A.T.,University of KwaZulu - Natal | Beletse Y.G.,Vegetable and Ornamental Plant Institute VOPI
Agricultural Water Management | Year: 2013

Taro [Colocasia esculenta (L.) Schott] is an underutilised crop in sub-Saharan Africa due to lack of agronomic research on it. There is no information describing water-use and drought tolerance of local taro landraces. Therefore, the objective of this study was to evaluate growth, yield and water-use of three South African landraces of taro under varying water regimes. Three taro landraces [Dumbe Lomfula (DL), KwaNgwanase (KW) and Umbumbulu (UM)] were planted in a rainshelter (14, October, 2010 and 8, September, 2011) at Roodeplaat, Pretoria, South Africa. Three levels of irrigation [30%, 60% and 100% crop water requirement (ETa)] were applied three times a week using drip irrigation. Emergence, plant height, leaf number, leaf area index (LAI) and stomatal conductance were measured in situ. Root length, fresh and dry mass were obtained by destructive sampling. Yield, yield components and water-use efficiency were determined at harvest. Taro landraces showed slow and uneven emergence. Stomatal conductance was respectively, 4% and 23% lower at 60% and 30% ETa relative to 100% ETa. Such a decline was clearer in the UM landrace, suggesting greater stomatal regulation in the UM landrace compared with KW and DL landraces. Plant growth parameters (plant height, leaf number and LAI) were shown to decrease by between 5% and 19% at 60% and 30% ETa, respectively, evapotranspiration relative to 100% ETa. The KW and DL landraces were shown to decrease the most while the UM landrace had moderate reductions in growth. Taro yield was 15% and 46% higher at optimum irrigation relative to 60% ETa and 30% ETa, respectively. Water-use efficiency was relatively unchanged (0.22-0.24kgm-3) across varying water regimes. On average, the UM landrace had 113% higher WUE than the KW landrace. These findings can be used to differentiate the landraces on the basis of potential drought tolerance. © 2013 Elsevier B.V.


Mabhaudhi T.,University of KwaZulu - Natal | Modi A.T.,University of KwaZulu - Natal | Beletse Y.G.,Vegetable and Ornamental Plant Institute VOPI
Agricultural and Forest Meteorology | Year: 2014

Promotion of taro, a neglected underutilised crop, as a possible future crop under water-limited conditions hinges on availability of information describing its yield responses to water. Therefore, AquaCrop was calibrated and validated for the first time for an eddoe type taro landrace from South Africa, using data from pot, field and rain shelter experiments conducted over two seasons (2010/11 and 2011/12) at two locations (Pretoria and Pietermaritzburg) representative of semi-arid climates. Observed weather and soil physical parameters for specific sites together with measured crop parameters from optimum experiments conducted during 2010/11, were used to develop climate, soil and crop files in AquaCrop and to calibrate the model. Observations from the 2011/12 growing season and independent data were used to validate the model. Model calibration showed a good fit (R2=0.789; d-index=0.920; RMSE=2.380%) for canopy cover (CC) as well as good prediction for final biomass (RMSE=1.350tha-1) and yield (RMSE=1.205tha-1). Model validation showed good simulation for CC under irrigated conditions (R2=0.844; d-index=0.998; RMSE=1.852%). However, the model underestimated CC under rainfed (R2=0.018; d-index=0.645; RMSE=20.170%) conditions. The model predicted biomass (R2=0.898; d-index=0.875; RMSE=5.741tha-1) and yield (R2=0.964; d-index=0.987; RMSE=1.425tha-1) reasonably well for pooled data [field (RF and FI) and rain shelter (100, 60 and 30% ETa)]. The model also predicted biomass (R2=0.996; d-index=0.986; RMSE=1.745tha-1) and yield (R2=0.980; d-index=0.991; RMSE=1.266tha-1) well for the independent data set. © 2014 Elsevier B.V.


Mabhaudhi T.,University of KwaZulu - Natal | Modi A.T.,University of KwaZulu - Natal | Beletse Y.G.,Vegetable and Ornamental Plant Institute VOPI
Agronomy Journal | Year: 2014

The aim of this study was to parameterize and test the generic crop model AquaCrop for a local bambara groundnut [Vigna subterranea (L.) Verdc] landrace. Such a model should be water driven and assist in the promotion of neglected and underutilized species as possible future crops under water-limited conditions. AquaCrop was parameterized for a South African bambara groundnut landrace using data from controlled field and rain shelter experiments conducted during two seasons (2010/2011 and 2011/2012) at Pretoria, South Africa. Observed weather, soil physical, and measured crop parameters from optimum experiments conducted during 2010/2011 were used to develop respective climate, soil, and crop files in AquaCrop and to parameterize the model. Model parameterization for bambara groundnut showed a very good fit for canopy cover (R2 = 0.94, Willmott's d index of agreement = 0.99, RMSE = 3.37%) and biomass (R2 = 0.96, d index = 0.99, RMSE = 1.29 Mg ha-1). The model also predicted final biomass (RMSE = 1.70 Mg ha-1) and yield (RMSE = 0.29 Mg ha-1) reasonably well. Model testing showed good fit for canopy cover under irrigated (R2 = 0.86, d index = 0.96, RMSE = 9.72%) and rainfed field conditions (R2 = 0.95, d index = 0.97, RMSE = 6.18%) compared with simulation of results from rain shelter experiments. The model simulated final biomass and yield of bambara groundnut very well under field conditions. The model's performance under rainfed conditions make it particularly suited for extrapolation to marginal areas of agricultural production in South Africa and the region. © 2014 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved.


Prinsloo G.,Vegetable and Ornamental Plant Institute VOPI | Viljoen J.C.,Vegetable and Ornamental Plant Institute VOPI | Du Plooy C.P.,Vegetable and Ornamental Plant Institute VOPI
Acta Horticulturae | Year: 2011

Leonotis leonurus is also known as wild dagga, lebake (Sotho, Tswana) or wilde dagga (Afrikaans). This plant with its attractive orange flowers can grow up to five meters high. The whole plant is strongly aromatic. The leaves and roots are used to treat coughs, colds, influenza, high blood pressure, headaches and bronchitis. Little or no information is available on cultivation of South African medicinal plants. To resolve this, research is conducted to determine the effects of cultivation on the yield and medicinal properties of the plants. The fresh mass yield was recorded and the changes in chemical composition were determined by chromatographic methods and performing bioassays after the plants were fertilised with three different inorganic nitrogen fertilisers. Limestone ammonium nitrate (LAN), ureum and ammonium sulphate was used as fertiliser treatments at 0 (control), 180, 240, 300 and 360 kg N/ha. The recommended fertiliser application was determined to be 180 kg N/ha ammonium sulphate with a yield of 34.4 t/ha fresh mass. The plant material was extracted and subjected to general screening on two gram positive human pathogens namely Enterococcus faecalis, Staphyllococcus aureus and one gram negative bacterium Escherischia coli to determine the effect on the biological activity. Only minor changes were observed in the chemical composition and the Minimum Inhibitory Concentration (MIC) of the extracts against the microorganisms. These differences are probably due to natural variation that exists in the plants as the medicinal properties were not compromised.

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