Responses of maize (Zea mays L.) landraces to water stress compared with commercial hybrids.

Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.Local maize landraces have evolved over hundreds of years of natural and farmer selection under varying conditions. These landraces may have developed tolerance to abiotic stresses such as water deficits during this cycle of selection. However, despite its continued existence and importance, little is known on their agronomy and responses to water stress. If indeed landraces have developed tolerance to water stress, they may prove a key genetic resource for future crop improvement in light of increasing water scarcity. The primary objective of this study was to evaluate the responses of a local maize landrace to water stress at different stages of growth in comparison to two known commercial hybrids, SC701 and SR52. Seed from a local maize landrace was multiplied and characterised according to kernel colour. Two distinct colours were selected for the purposes of this study, white (Land A) and dark red (Land B). In a holistic approach, the thesis consisted of four separate studies whose overall objective was to evaluate the responses of the maize landraces to water stress at different growth stages, up to and including yield and its components. These comprised three controlled environment studies (25°C; 60% RH) and a field trial. For the controlled environment, two water regimes were used, 25% field capacity (FC) (stress treatment) and 75% FC (non-stress). The first study investigated the effect of water stress on early establishment performance. Seed quality was evaluated using the standard germination test together with electrolyte leakage. Catalase activity and accumulation of proline were examined as seedling physiological response to water stress. The second study was conducted as a pot trial to investigate the effect of water stress on growth, photosynthesis and yield. Photosynthesis was measured as chlorophyll fluorescence (CF). In addition, a field study over three planting dates was conducted at Ukulinga Research Farm in Pietermaritzburg, under dryland conditions, during the period from August 2008 to June 2009. The objective was to evaluate the effect of planting dates and changing soil water content on growth, yield and yield components. Three planting dates were used, representative of early (28 August 2008), optimum (21 October 2008) and late planting (9 January 2009). Lastly, a study on hydro-priming was conducted, necessitated by observations made primarily in the first study. The study was carried out under controlled environment conditions. The objective was to evaluate whether hydropriming can improve germination, vigour and emergence under water stress. Seeds were soaked in water for 0 hours (Un-primed or control), 12 hours (P12) and 24 hours (P24). Results from the first study showed that maize landraces were slower to germinate and emerge, and produced less vigorous seedlings compared to the hybrids. The study showed that hybrids were more superior under optimum (75% FC) conditions than under stress conditions (25% FC). Physiological showed that both hybrids and landraces expressed catalase under water stress, with landraces showing slightly better expression compared to the hybrids. Proline accumulation was observed in both hybrids and landraces as a response to water stress, with hybrids being more sensitive to water stress. In the pot trial, results showed that the vegetative stage of both hybrids and landraces was less sensitive to water stress than the reproductive stage. Results showed no differences between field capacities, with respect to emergence, mean emergence time, leaf number, CF, ear prolificacy and ear length. Photosynthesis, as measured by CF, was shown to be desiccation tolerant. Water stress had a negative effect on cob mass, lines per cob, grains per cob and total grain mass, and resulted in barrenness in the landraces. The hybrids had superior yield compared to the landraces. Results for the field trials showed that planting date had highly significant effects on emergence, plant height, leaf number and days to tasseling (DTT). Landraces emerged better than hybrids in all plantings; highest emergence was in the early and late plantings. Optimum and late planting resulted in maximum plant height and leaf number, respectively, compared to early planting. Hybrids were superior, growing taller and with more leaves than landraces in all plantings. DTT decreased with successive plantings. Planting date had an effect on ear prolificacy (EP), kernels/ear (KNE) and 100 grain mass. Planting date had no effect on ear length and mass, kernel rows/cob, grain mass and yield. With the exception of EP, hybrids out-yielded the landraces in all three planting dates. Hydro-priming landraces for 12 hours and 24 hours, respectively, improved germination velocity index, reduced mean germination time and improved emergence and mean emergence time of maize landraces under water stress. Performance of hybrid seeds remained superior to that of landraces even after seed treatment to improve germination and vigour. Landraces were slower to germinate and emerge and produced less vigorous seedlings in controlled conditions only. Both hybrids and landraces expressed catalase activity and also accumulated proline in response to water stress, although hybrids were more sensitive to stress in the establishment phase. Results confirmed literature, showing that, for both hybrids and landraces, the vegetative stage is less sensitive to stress than the reproductive stage. Hybrids produced superior yields compared to landraces in both controlled environment and field conditions. However, the pattern of seedling establishment observed in the initial controlled environment study for hybrids and landraces was reversed in the field study. Lastly, hydro-priming is of some benefit to maize establishment

Drought tolerance and water-use of selected South African landraces of Taro (Colocasia esculenta L. schott) and Bambara groundnut (Vigna subterranea L. Verdc)

Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.Issues surrounding water scarcity will become topical in future as global fresh water resources become more limited thus threaten crop production. Predicted climate change and increasing population growth will place more pressure on agriculture to produce more food using less water. As such, efforts have now shifted to identifying previously neglected underutilised species (NUS) as possible crops that could be used to bridge the food gap in future. Taro (Colocasia esculenta L. Schott) and bambara groundnut (Vigna subterranea L. Verdc) currently occupy low levels of utilisation in South Africa. Both crops are cultivated using landraces with no improved varieties available. Information describing their agronomy and water–use is limited and remains a bottleneck to their promotion. The aim of this study was to determine the drought tolerance and water–use of selected landraces of taro and bambara groundnut from KwaZulu-Natal, South Africa. In order to meet the specific objectives for taro and bambara groundnut management, an approach involving conventional and modelling techniques was used. Three taro landraces [Dumbe Lomfula (DL), KwaNgwanase (KW) and Umbumbulu (UM)] were collected from the North Coast and midlands of KwaZulu-Natal, South Africa, in 2010. The UM landrace was classified as Eddoe type taro (C. esculenta var. antiquorum) characterised by a central corm and edible side cormels. The DL and KW landraces were classified as Dasheen (C. esculenta var. esculenta), characterised by a large edible main corm and smaller side cormels. A bambara groundnut landrace was collected from Jozini, KwaZulu- Natal, and characterised into three selections (‘Red’, ‘Light-brown’ and ‘Brown’) based on seed coat colour. Seed colour was hypothesised to have an effect on seed quality. Field and rainshelter experiments were conducted for both taro and bambara landraces at Roodeplaat in Pretoria and Ukulinga Research Farm in Pietermaritzburg, over two growing seasons (2010/11 and 2011/12). The objective of the field trials for taro and bambara groundnut was to determine mechanisms associated with drought tolerance in taro and bambara groundnut landraces. Experiments were laid out in a split-plot design where irrigation [fully irrigated (FI) and rainfed (RF)] was the main factor and landraces (3 landraces of either taro or bambara groundnut) were sub-factors. Treatments were arranged in a randomised complete block design (RCBD), replicated three times. Rainfed trials were established with irrigation to allow for maximum crop stand. Thereafter, irrigation was withdrawn. Whilst experimental designs and layouts for taro and bambara groundnut were similar, differences existed with regards to plot sizes and plant spacing. Trials were planted on a total land area of 500 m2 and 144 m2, for taro and bambara groundnut, respectively. Plant spacing was 1 m x 1 m for taro and 0.3 m x 0.3 m for bambara groundnut. Irrigation scheduling in the FI treatment was based on ETo and Kc and was applied using sprinkler irrigation system. Separate rainshelter experiments were conducted for taro and bambara groundnut landraces at Roodeplaat, to evaluate growth, yield and water-use of taro and bambara groundnut landraces under a range of water regimes. The experimental design was similar for both crops, a RCBD with two treatment factors: irrigation level [30, 60 and 100% crop water requirement (ETa)] and landrace (3 landraces), replicated three times. Irrigation water was applied using drip irrigation system based on ETo and Kc. Data collection in field and rainshelter trials included time to emergence, plant height, leaf number, leaf area index (LAI), stomatal conductance and chlorophyll content index (CCI). For taro field trials, vegetative growth index (VGI) was also determined. Yield and yield components (harvest index, biomass, corm number and mass) as well as water–use efficiency (WUE) were determined at harvest. Intercropping of taro and bambara groundnut was evaluated under dryland conditions using farmers’ fields at Umbumbulu, KwaZulu–Natal, South Africa. The experimental design was a RCBD replicated three times. Intercrop combinations included taro and bambara groundnut sole crops, a 1:1 (one row taro to one row bambara groundnut) and 1:2 intercrop combinations. The taro UM landrace and ‘Red’ bambara groundnut landrace selection were used in the intercropping study. Lastly, data collected from field and rainshelter experiments were used to develop crop parameters to calibrate and validate the FAO’s AquaCrop model for taro and bambara groundnut landraces. The UM landrace was used for taro while the ‘Red’ landrace selection was used for bambara groundnut. AquaCrop was calibrated using observed data from optimum (FI) experiments conducted during 2010/11. Model validation was done using observations from field and rainshelter experiments conducted during 2011/12 as well as independent data. Results showed that all taro landraces were slow to emerge (≈ 49 days after planting). Stomatal conductance declined under conditions of limited water availability (RF, 60% and 30% ETa). The UM landrace showed better stomatal regulation compared with KW and DL landraces under conditions of limited water availability. Plant growth (plant height, leaf number, LAI and CCI) of taro landraces was lower under conditions of limited water availability (RF, 60% and 30% ETa) relative to optimum conditions (FI and 100% ETa). The UM landrace showed moderate reductions in growth compared with the DL and KW landraces, suggesting greater adaptability to water limited conditions. The VGI showed a large reduction in growth under RF conditions and confirmed the UM landrace’s adaptability to limited water availability. Limited water availability (RF, 60% and 30% ETa) resulted in lower biomass, HI, and final yield in taro landraces relative to optimum conditions (FI and 100% ETa). For all trials, the DL landrace failed to produce any yield. WUE of taro landraces was consistent for the three irrigation levels (30, 60 and 100% ETa); however, on average, the UM landrace was shown to have a higher WUE than the KW landrace. Bambara groundnut landraces were slow to emerge (up to 35 days after planting). ‘Red’ and ‘Brown’ landrace selections emerged better than the ‘Light-brown’ landrace selection, confirming the effect of seed colour on early establishment performance. Plant growth (stomatal conductance, CCI, plant height, leaf number, LAI and biomass accumulation) was lower under conditions of limited water availability (RF, 60% and 30% ETa) relative to optimum conditions (FI and 100% ETa). The ‘Red’ landrace selection showed better adaptation to stress. Limited water availability resulted in early flowering and reduced flowering duration as well as early senescence and maturity of bambara groundnut landrace selections. The ‘Red’ landrace selection showed delayed leaf senescence under conditions of limited water availability. Yield reductions of up to 50% were observed under water limited conditions (RF, 60% and 30% ETa) relative to optimum conditions (FI and 100% ETa). Water use efficiency increased at 60% and 30% ETa, respectively, relative to 100% ETa, implying adaptability to limited water availability. The ‘Red’ landrace selection showed better yield stability and WUE compared with the ‘Brown’ and ‘Light-brown’ landrace selections suggesting that seed colour may be used as a selection criterion for drought tolerance in bambara groundnut landraces. The intercropping study showed that intercropping, as an alternative cropping system, had more potential than monocropping. Evaluation of growth parameters showed that taro plant height was generally unaffected by intercropping but lower leaf number was observed as compared with the sole crop. Bambara groundnut plants were taller and had more leaves under intercropping relative to the sole crop. Although not statistically significant, yield was generally lower in the intercrops compared with the sole crops. Evaluation of intercrop productivity using the land equivalent ratio (LER) showed that intercropping taro and bambara groundnut at a ratio of 1:1 was more productive (LER = 1.53) than intercropping at a ratio of 1:2 (LER = 1.23). The FAO’s AquaCrop model was then calibrated for the taro UM landrace and ‘Red’ bambara groundnut landrace selection. This was based on observations from previous experiments that suggested them to be drought tolerant and stable. Calibration results for taro and bambara groundnut landraces showed an excellent fit between predicted and observed parameters for canopy cover (CC), biomass and yield. Model validation for bambara groundnut showed good model performance under field (FI and RF) conditions. Model performance was satisfactory for rainshelters. Validation results for taro showed good model performance under all conditions (field and rainshelters), although the model over-estimated CC for the declining stage of canopy growth under RF conditions. Model verification using independent data for taro showed equally good model performance. In conclusion, the taro UM landrace and ‘Red’ bambara groundnut landrace selection were shown to be drought tolerant and adapted to low levels of water–use. The mechanisms responsible for drought tolerance in the taro UM landrace and ‘Red’ bambara groundnut landrace selection were described as drought avoidance and escape. The taro UM landrace and ‘Red’ bambara groundnut landraces avoided stress through stomatal regulation, energy dissipation (loss of chlorophyll) as well as reducing canopy size (plant height, leaf number and LAI), which translates to minimised transpirational water losses. This indicated landrace adaptability to low levels of water–use. The ‘Red’ bambara groundnut landrace selection showed phenological plasticity and escaped drought by flowering early, delaying leaf senescence, and maturing early under conditions of limited water availability. Performance of the ‘Red’ landrace selection lends credence to the use of seed coat colour as a possible selection criterion for drought tolerance in bambara groundnut, and possibly for other landraces with variegated seed. The taro UM landrace escaped drought by maturing early under conditions of limited water availability. The FAO’s AquaCrop model was successfully calibrated and validated for taro UM and ‘Red’ bambara groundnut landraces. The calibration and validation of AquaCrop for taro is the first such attempt and represents progress in the modelling of neglected underutilised crops. The calibration and validation of AquaCrop for taro requires further fine-tuning while that for bambara groundnut still needs to be tested for more diverse landraces

Effect of Moistube and subsurface drip irrigation on cowpea (Vigna unguiculata (l.) Walp) production in South Africa

Moistube irrigation (MTI) is a new subsurface irrigation technology where the water emits from a semipermeable membrane at a slow rate  depending on applied pressure and soil water potential. There is lack of information on how various crops respond to MTI. This study determined growth, yield and water use efficiency (WUE) of cowpea (Vigna unguiculata (L.) Walp) under varying water regimes under MTI and subsurface drip irrigation (SDI), using field and glasshouse experiments in summer and winter of 2018, respectively. A splitplot design arranged in randomized complete blocks, replicated 3 times, with SDI as the control experiment was used. The main plot was irrigation type while the sub-plots were the water regimes. The water treatments consisted of full irrigation (100% of crop water requirement (ETc)), and deficit irrigation (DI) of 70% ETc and40% ETc. Water deficit had a significant effect (p < 0.05) on time to flowering; plants under 40% ETc flowered 14 days earlier than plants at 100% ETc. There were significant (p < 0.05) differences in yield components. Grain yields were 1 280 kg∙ha–1, 2 401 kg∙ha–1 and 3 189 kg∙ha–1 for 40% ETc, 70% ETc and 100% ETc, respectively, but no significant (p > 0.05) differences were recorded between SDI and MTI. However, at 40% ETc, SDI had 15% higher yield than MTI. Biomass varied significantly (p < 0.05) with irrigation type and water treatment. Grain WUE varied significantly (p < 0.05) among the water regimes. The highest WUE was achieved under SDI at 70% ETc but was not significantly different from that under MTI at 70% ETc. In conclusion, performance of cowpea was similar under the two irrigation systems under moderate DI but was better for SDI under severe DI with respect to biomass and WUE for the summer trial. Moderate DI improved the grain WUE while all the DI conditions improved the biomass WUE. Keywords: crop growth deficit irrigation indigenous legume irrigation semi-permeable membrane water use efficiency yiel

Calibration and Evaluation of the FAO AquaCrop Model for Canola (Brassica napus) under Varied Moistube Irrigation Regimes

The AquaCrop model was calibrated and validated for canola (Brassica napus) under Moistube irrigation (MTI) and various water regimes [(i) 100%, (ii) 75%, and (iii) 55% of crop water requirement (ETc)] over two seasons, 2019 and 2020. The normalised root mean square (nRMSE), Model Efficiency (EF), R2, and the Willmot’s index of agreement (d) statistics were used to evaluate the model’s efficiency in simulating biomass (B), canopy cover (CC), yield (Y), and harvest index (HI). The calibration results indicated the model simulated with accuracy the CC (under 100% ETcR2 = 0.99, EF = 0.92, nRMSE = 6.4%, d = 0.98) and 75% ETc (R2 = 0.99, EF = 0.92, nRMSE = 10.3%, d = 0.98). The model simulated CC well for validation for 100% ETc (R2 = 0.97, EF = 0.93, nRMSE = 22.5%, d = 0.98) and 75% ETc (R2 = 0.84, EF = 0.45, nRMSE = 59.2%, d = 0.86) irrigation regimes. Final biomass simulations were reasonably good under 100% ETc, 75% ETc, and 55% ETc irrigation regimes (R2 > 0.90, d > 0.65). The study showed the usefulness of AquaCrop for assessing yield response of canola to full and deficit irrigation scenarios under MTI

Water use of sorghum (Sorghum bicolor L. Moench) in response to varying planting dates evaluated under rainfed conditions

It is vital to understand how rainfall onset, amount and distribution between planting dates affect sorghum yield and water use, in order to aid planting date and cultivar selection. This study investigated morphological, physiological, phenological, yield and water use characteristics of different sorghum genotypes in response to different planting dates under rainfed conditions. Four genotypes (PAN8816 [hybrid], Macia [open-pollinated variety, OPV], Ujiba and IsiZulu [both landraces]) were planted on 3 planting dates (early, optimal, and late) in a split-plot design, with planting dates as the main factor. Low soil water at the optimal planting date was associated with delayed crop establishment and low final emergence. Sorghum genotypes adapted to low and irregular rainfall at the late planting date through low leaf number, canopy cover, chlorophyll content index and stomatal conductance, and hastened phenological development. This resulted in low biomass and grain yields. Landraces exhibited grain yield stability across planting dates, whilst OPV and hybrid genotypes significantly reduced grain yield in response to low water availability when planted late. Biomass and grain yield water use efficiency (WUE) were highest at optimal planting date (30.5 and 9.2 kg∙ha-1·mm-1), relative to late (23.1 and 8.7 kg·ha-1·mm-1), and early planting dates (25.2 and 8.3 kg·ha-1·mm-1). For PAN8816 and Macia, biomass and grain WUE decreased in response to low soil water content, and irregular and disproportionate rainfall experienced during the late planting date. By contrast, biomass and grain WUE for Ujiba and IsiZulu improved with decreasing rainfall. PAN8816 is recommended when planting under low soil water availability to maximize crop stand. Cultivation of Macia is recommended under optimal conditions. Ujiba and IsiZulu landraces are recommended for low rainfall areas with highly variable rainfall. Repetition or modelling of genotype responses across environments different from Ukulinga is required for thorough water use characterisation of these genotypes.Keywords: planting dates, water use efficiency, rainfall variability, cultivar selection, landraces and improved sorghum varietie

An analysis of the perceived societal benefits of and threats from trees for the delivery of livelihoods and community development

Societal Impact Statement Understanding the perceptions of benefits and threats from trees is important for the livelihoods of communities. The study used focus group discussions, key informant interviews, and a questionnaire survey of 226 households in the province of KwaZulu‐Natal, South Africa. The findings showed that household socio‐economic factors such as gender and land tenure influenced perceptions of tree growing, and households that were involved in a tree restoration project viewed trees as contributing toward their livelihoods by reducing hunger. Hence there is a need to design strategies that promote socio‐economic inclusivity of all households and genders and promote programs that increase awareness of ecosystem services within communities. Summary Understanding the socio‐economic factors that shape the way households value and utilize natural resources is critical in developing nature‐based solutions. The study was aimed at understanding how the socio‐economic circumstances of households determined their perceptions of the role of trees in livelihood delivery. A case study of Buffelsdraai and Osindisweni communities was used; these sites are adjacent to a municipal landfill where a tree restoration project intended to mitigate the effects of climate change is being implemented, and some of the households are involved in this project. The study used focus group discussions, key informant interviews, and a questionnaire survey of 226 households. It explored gender perspectives on the perceived benefits and threats of tree restoration. It analyzed the influence of households' economic characteristics and spatial configuration (the subdivisions of the landscape) to assess the impact of land tenure. The findings showed that gender influenced the perceptions that economic benefits can be derived from participating in the project. Households involved in the tree restoration project viewed trees as contributing to their livelihoods by reducing hunger. Households in peri‐urban settlements, permanently resident in the area, showed greater reliance on natural resources than those in informal settlements and rural areas. Such differences can be attributed to differences in land tenure. Hence, there is a need to design strategies and operations that promote socio‐economic inclusivity of all households and genders and reduce inequality. These findings are important for informing scaling to yield better climate change considerations and policies

Investigation of the optimum planting dates for maize varieties using a hybrid approach: A case of Hwedza, Zimbabwe.

Water scarcity and unreliable weather conditions frequently cause smallholder farmers in Zimbabwe to plant maize (Zea mays L.) varieties outside the optimum planting timeframe. This challenge exacts the necessity to develop sowing management options for decision support. The study's objective was to use a hybrid approach to determine the best planting windows and maize varieties. The combination will guide farmers on planting dates, dry spell probability during critical stages of the crop growth cycle and rainfall cessation. To capture farmer's perception on agroclimatic information, a systematic random sampling of 438 smallholders was carried out. An analysis of climatic data during 1949-2012 was conducted using INSTAT to identify the best planting criterion. The best combination of planting criterion and maize varieties analysis was then achieved by optimizing planting dates and maize varieties in the DSSAT environment. It was found that 56.2% of farmers grew short-season varieties, 40.2% medium-season varieties and 3.6% long-season varieties. It was also established that the number of rain days and maize yield had a strong positive relationship (p = 0.0049). No significant association was found amongst maize yield (p > 0.05), and planting date criteria, Depth (40mm in 4 days), the AREX criterion- Agricultural Research Extension (25 mm rainfall in 7 days) and the MET Criterion-Department of Meteorological Services (40 mm in 15 days). Highest yields were simulated under the combination of medium-season maize variety and the AREX and MET criteria. The range of simulated yields from 0.0 t/ha to 2.8 t/ha formed the basis for the development of an operational decision support tool (cropping calendar) with (RMSE) (0.20). The methodology can be used to select the best suitable maize varieties and a range of planting time

Policy gaps and food systems optimization: a review of agriculture, environment, and health policies in South Africa

South Africa faces the triple burden of malnutrition, high poverty levels, unemployment, and inequality. “Wicked problems” such as these require innovative and transdisciplinary responses, multi-stakeholder coordination and collaboration, managing complex synergies and trade-offs, and achieving sustainable outcomes. Through qualitative content analysis of national and provincial sector-based policies, we explored the interlinkages between the agriculture, environment, and health sectors in South Africa in the context of sustainable food and nutrition security and the extent to which these interlinkages are integrated into policy and planning. A systemic analysis of the review outcomes was performed to identify its main learning outcome, the status quo in the policy process. The nature of feedback loops was identified, and a leverage point was suggested. The review highlighted that policymakers in the agriculture, environment and health sectors are aware of, and have understood, the relationships among the three sectors. They have also made attempts to address these interlinkages through collaboration and coordination. Unfortunately, this has been met with several challenges due to fragmented sector-specific mandates and targets and a lack of resources for integrated solutions. This creates implementation gaps and unintended duplication of activities, leading to poor service delivery. Transitioning to sustainable and healthy food systems will only be possible after these gaps have been closed and implementation optimization has been achieved. Focusing on meta-level problem-framing, functional collaboration through transdisciplinary approaches, and integrated targets are critical to successful policy implementation and progressive realization of national goals related to sustainable food and nutrition security, unemployment, poverty, and inequality