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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.

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 (0.22–0.24 kg m−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.

Bambara groundnut (Vigna subterranea (L.) Verdc.) is an underutilised species with potential to contribute nutritional and food security in marginal areas. Growth, phenology and yield of a local bambara groundnut landrace from Jozini, KwaZulu-Natal, characterised into three selections according to seed coat colour, namely Brown, Red and Light Brown, were evaluated under irrigated and rain-fed field conditions at Roodeplaat, Pretoria, over two seasons (2010/11 and 2011/12). Trials with three replicates were planted under rain-fed and irrigated conditions with seed colour as a subfactor. Emergence (up to 35 d after planting), plant height, leaf number, leaf area index, chlorophyll content index and stomatal conductance were measured in situ. Yield and components of yield were determined at harvest. The Red, Brown and Light Brown landrace selections emerged well (84%, 81% and 51%, respectively). Plant physiological and growth parameters of stomatal conductance, chlorophyll content index, plant height, leaf number, leaf area index and biomass accumulation were lower under rain-fed relative to irrigated conditions. Adaptations were landrace selection-specific, with the Brown and Red landrace selections showing better adaptation to rain-fed conditions. Under rain-fed conditions, bambara groundnut landrace selections flowered, senesced and matured earlier relative to irrigated conditions. Consequently, there were lower yields under rain-fed compared with irrigated conditions. The Red and Brown landrace selections may have drought-avoidance mechanisms. Seed colour may be used as a selection criterion for drought tolerance in bambara groundnut landraces.

The 2013 AAEA & CAES Joint Annual Meeting in Washington, DC will offer AAEA members, CAES members, and other applied economists a chance to interact and learn over the course of the three day meeting on August 4-6. This year’s meeting features a large amount of educational content including:

More than 150 educational sessions

Over 200 posters on display, with opportunities to interact with their authors

Multiple plenary sessions each day, featuring high-profile speakers

Common research topics include:

International development

Climate change

Biofuels

Linkages between food and health

The Farm Bill

Land use and water resource issues

Regional economics

Business economics

Behavioral economics

The meeting will also feature a number of chances for attendees to connect and network at the welcome and closing receptions, receptions for specific Sections of AAEA, and evening gatherings organized by universities and government agencies.

Maize (Zea mays L.) is the major grain crop in South Africa where most subsistence farmers still plant landraces. The objective of this study was to compare two landrace selections of maize with two hybrids popular among small-scale farmers in KwaZulu-Natal, for seed performance and water stress tolerance during seedling establishment. Two variations of a local landrace, white (Land A) and dark red (Land B), were compared to two hybrids, SC701 and SR52. Standard germination test and electrical conductivity were used to assess seed quality under laboratory conditions. Seedling emergence was performed in seedling trays using pine bark at 25% and 75% field capacity (FC), respectively, over a period of 21days. All seed types showed high germination capacity (>93%). There were highly significant differences (p<0.001) among seed types with respect to daily germination and germination velocity index (GVI). Landraces germinated slower than the hybrids. Landraces showed a 20% better root length and 41% lower electrolyte leakage than hybrids. There were differences (p<0.001) in seedling emergence between 25%FC and 75%FC. Hybrids showed better emergence at 75% FC. At 25% FC seedling emergence was drastically reduced (>5% in all varieties). Hybrids emerged faster than the landraces in both water regimes. Landraces performed better than hybrids under stress conditions. This study showed that landraces may have the same viability as hybrids and a better tolerance to stress during early establishment of the crop.

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.

Historically, traditional cropping systems are based on diversification, thus making a significant contribution to food security for the household. Intercropping may offer farmers the opportunity to mimic this diversity. The aim of this study was to evaluate the productivity of a taro-bambara intercrop. The intercrop combinations were 1:1 and 1:2, compared with taro and bambara sole crops. Growth parameters and yield components were determined separately for each crop. Thereafter, land equivalent ratio (LER) was calculated to evaluate the productivity of the intercrop. Plant height of taro, as the main crop, was not significantly affected by intercropping. However, leaf number was significantly affected (P<0.001). Intercropping taro resulted in reduced leaf number compared with the sole crop; leaf number in response to the 1:2 intercrop was significantly lower than that of 1:1 intercrop. Bambara growth was significantly (P<0.05) affected by intercropping in that plants were taller and had more leaves when intercropped with taro. Taro yield was not significantly affected by intercropping, although yield generally decreased under intercropping compared with the sole crop. Bambara yield was also not significantly affected by intercropping. The LER showed that intercropping was more productive than sole cropping. The 1:1 intercrop had a LER of 1.71 compared with 1.36 for the 1:2 intercrop. It is concluded that although intercropping had variable effects on the growth of both taro and bambara, there was an agronomic advantage to intercropping.