Case Study

Bottle gourd (Lagenaria siceraria (Molina) Standl.) is an indigenous crop that is available only as landraces in sub-Saharan Africa, although it has a great potential for food security. Pumpkin (Cucurbita maxima L.) and cucumber (Cucurbita pepo L.) are exotic crops that have similar food roles as bottle gourd. There is no information on the seed quality of bottle gourd landraces found in sub-Saharan Africa. It was hypothesised that the hybrid seeds of closely related species would have better seed quality than bottle gourd landraces. Three landraces of bottle gourd were compared with two pumpkin cultivars and one cucumber cultivar for germination capacity and associated parameters (mean germination time and germination velocity index) as well as seedling establishment. Results showed that the germination trend was similar for all varieties, but there was a significant (P<0.05) difference among them with respect to all parameters. There was no distinct evidence of differences in seed quality to permit separation of seeds by species. It was concluded that bottle gourd landrace seed quality is comparable to the hybrids of pumpkin and cucumber and the established recommendations for testing the seeds of hybrids can be used to test the landraces.

Water is the main factor affecting crop production in sub-Saharan Africa. It was hypothesized that intercropping sorghum (S) with either cowpea (C) or bottle gourd (B) would result in better productivity and water use efficiency (WUE). This was evaluated using a split-plot design with sub-plots arranged in a randomised complete block manner within the main plot, replicated thrice. Water regimes [full irrigation (FI), deficit irrigation (DI) and rainfed (RF)] were allocated to the main plots. Sub-plots comprised intercrop combinations, SS (sole), C (sole), B (sole), SC (intercrop) and SB (intercrop). Data collected included soil water content (SWC), plant height (PH)/vine length, leaf number (LN), tillering (T)/branching, leaf area index (LAI), relative leaf water content (RWC), stomatal conductance (gs) and chlorophyll content index (CCI) as well as biomass accumulation and partitioning. Yield and yield components, water use (WU) and WUE for grain (WUEg) were calculated at harvest. Land equivalent ratio (LER) was used to evaluate productivity of the intercrop. Sorghum canopy size decreased (P < 0.05) (−6.7%, −10.6%, −89% and −79% for PH, LN, T and LAI, respectively) with decreasing water availability. Sorghum growth and development were unaffected by intercropping. Intercropping sorghum with cowpea improved gs (23%) and CCI (6.56%) of sorghum under low water availability. Productivity of sorghum across varying water regimes and cropping systems was stable with final biomass, yield and harvest index of 2.4 t ha−1, 0.98 t ha−1 and 35%, respectively. Overall, LER showed a 46% increase in productivity across all intercrop systems. Intercropping marginally increased WU (5.64%). Improvements of WUEg were observed under SC and SB (54.65% and 46.98%, respectively) relative to SS. Intercropping sorghum with cowpea is recommended for semi-and arid environments since it promoted efficient use of water.

Farmers who still cultivate bambara groundnut (Vigna subterranea) rely on landraces and seed retained from previous harvests. Given that the crop is typically cultivated in semi-arid regions, seed quality of farmers’ retained seed might be compromised due to water stress experienced by maternal plants during production. The aim of this study was to determine the effect of water stress on maternal plants on subsequent seed quality of bambara groundnut. A single bambara groundnut landrace was characterised into four distinct selections based on seed coat and speckling colour. Initial seed quality (viability and vigour) was evaluated prior to planting seed in a field trial under irrigated and rainfed conditions. Final yield and yield components were determined at harvest. Thereafter, seed quality (viability and vigour) of progeny of different landrace selections was evaluated. Yield was lower under rainfed than irrigated conditions. Overall, subsequent seed quality showed improvement from initial seed quality of the original seedlot. Seed viability was higher in seeds produced under irrigated than rainfed conditions. Seed quality of bambara groundnut may be reduced underwater-limited production conditions. Seed enhancement practices such as priming may assist farmers to achieve better emergence. In the long term, seed production should be done under optimum conditions in order to achieve high-seed quality.

Three sweet potato cultivars (A40, A45 and 199062.1) were planted in three small-scale farms located under different agro-ecological zones of KwaZulu-Natal. The objective was to assess growth, physiological responses and yield of the sweet potato cultivars under low-input agricultural system and different environmental conditions. Sweet potato planted at Richards Bay (28°19'S; 32°06E), a coastal sandy soil location, recorded low stomatal conductance(SC; 102.2 m moles m−2 s−1) and chlorophyll content index (CCI; 29.4). This consequently resulted in reduced vine length, leaf number and branching of sweet potato plants. Environmental conditions in that location (Richards Bay) such as high evapotranspiration, high temperatures and low water retention capacity of sandy soils created drought stress condition. This caused reduction in photosynthetic activities and translocation to the harvestable plant parts. The other two locations (Deepdale at 28°01'S; 28°99'E and Umbumbulu at 29°98'S; 30°70'E) located further from the coast and characterized by clayey soils recorded higher SC and CCI. Branching and number of leaves were significantly influenced by locations and growing season while vine length varied with locations, indicating specific varietal adaptation. Biomass and storage root yield followed a similar trend as plant growth and physiology. Richards Bay recorded very low biomass and storage root yield (5.4 and 5.0 t ha−1) in both seasons while Deepdale recorded higher yields (42.0 t ha−1) during the first growing season. Yields reduced by 67% (13.6 t ha−1) in the second season. Storage root yields from Umbumbulu were stable in both growing seasons (29.4 and 28 t ha−1 during seasons one and two, respectively). Adding fertilizer only improved storage roots yield in Richards Bay, otherwise cultural practises were responsible for storage root yield increases in Deepdale and Umbumbulu. Orange-fleshed sweet potato cultivar A45 showed good environmental plasticity while cultivar 199062.1 responded well to fertilizer application. This indicated its suitability for use in food security programmes under low-input agriculture.

Amaranthus cruentus, Corchorus olitorius and Vigna unguiculata are traditional leafy vegetables with potential to improve nutritional security of vulnerable people. The promotion of these crops is partly hindered by the lack of agronomic information. The effect of plant spacing on growth, physiology and yield of these three leafy vegetables was evaluated under commercial-scale production at Roodeplaat, Pretoria over two summer seasons, 2011/12 and 2012/13. A randomised complete block design was used with plant density (100 000, 66 666 and 50 000 plants ha−1) as a factor. Chlorophyll content index (CCI), chlorophyll fluorescence, stomatal conductance, leaf number, leaf area index (LAI) and biomass were measured in situ. Planting at 100 000 plants ha−1 resulted in lower (P < 0.05) LAI, CCI and biomass per plant for A. cruentus and C. olitorius. Total yield of A. cruentus, C. olitorius andV. unguiculata was higher (P < 0.05) at 100 000 plants ha−1 relative to 50 000 and 66 666 plants ha−1. For A. cruentus and C. olitorius, higher leaf attributes (CCI, plant height, leaf number, biomass per plant and LAI) were obtained and this indicated that traditional leafy vegetables can be produced commercially under lower densities using a drip irrigation system. Using 66 666 plants ha−1 is suitable for commercial production of A. cruentus and C. olitorius, whereas 50 000 plants ha−1 may be recommended under low water availability. For V. unguiculata 100 000 plants ha−1 is recommended.

The project mainstreams the climate risk considerations in the Land Rehabilitation Programme of Lesotho for improved ecosystem resilience and reduced vulnerability of livelihoods to climate shocks.

Drought tolerance mechanisms of three taro landraces (Dumbe Lomfula (DL), KwaNgwanase (KW) and Umbumbulu (UM)) were evaluated under field conditions Pietermaritzburg, South Africa, over two summer seasons. Taro was slow to emerge (~ 49 days) and showed significant differences between landraces with respect to final emergence with DL never achieving a good crop stand. Growth (plant height, leaf number and LAI), VGI, SC and CCI were significantly lower under rainfed (RF) than irrigated conditions. RF conditions resulted in significantly lower biomass, HI, and final yield of taro landraces compared to irrigated conditions. The UM landrace avoided drought through increased stomatal regulation, lowering chlorophyll content, smaller canopy size and reduced growth period. It is concluded that among the three landraces, UM is suitable for production under water stress conditions, because it exhibited drought avoidance and escape mechanisms.

Bambara groundnut (Vigna subterranea L.) is an underutilised African legume that fits the same ecological niche as Arachis hypogea. It is still cultivated using landraces and little is known about their seed quality. The current study evaluated seed quality characteristics (viability and vigour) of a local landrace on the basis of seed coat and speckling colour (plain red, plain cream, black speckles and brown speckles). Standard germination and electrolyte conductivity (EC) tests were used to evaluate viability and vigour. Seed imbibition rate was evaluated using two imbibition methods (seed-testing water bath and seed soaking). For each method, seeds were weighed at intervals and their water activity determined. Electron microscopy was used to determine seed coat thickness. There were highly significant differences (P < 0.001) among landrace selections with respect to germination, EC as well as imbibition and water activity. Black-speckled landraces had the highest germination (87%) and the plain cream landrace selections had the lowest final germination (67%). Brown-speckled and plain cream seeds had the highest (1 400 µs g-1) and lowest EC (36 µs g-1), respectively. Imbibition rate and water activity showed much fluctuation. Electron microscopy revealed that brown-speckled seeds had the thickest (116 µm) and plain cream seeds had the thinnest (107.9 µm) seed coats. The study concluded that seed quality in bambara groundnut was associated with seed coat and speckling colour.

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 = 1.350 t ha−1) and yield (RMSE = 1.205 t ha−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 = 5.741 t ha−1) and yield (R2 = 0.964; d-index = 0.987; RMSE = 1.425 t ha−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 = 1.745 t ha−1) and yield (R2 = 0.980; d-index = 0.991; RMSE = 1.266 t ha−1) well for the independent data set.

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.