Thesis (MSc. (Botany)) -- University of Limpopo, 2015 / Soybean is an important source of high quality protein and oil for both humans and animals, especially in protein formulations for pharmaceutical and nutriceutical use. This crop is adversely affected by both biotic and abiotic stresses impacting on its productivity. Soybean productivity can be improved via techniques such Agrobacterium-mediated genetic transformation. Soybean is recalcitrant and depends on suitable explants from which new shoots can be regenerated and be amenable for transformation. The goal of this study was to produce transgenic soybean plants that are tolerant to drought stress through Agrobacterium tumefaciens-mediated transformation. Multiple shoot induction on double and single coty-node explants, obtained from soybean seedlings derived from seeds germinated in vitro on Murashige and Skoog culture medium supplemented with cytokinins was studied. The effect of different concentrations of benzyladenine (1.57, 2.00 and 4.00 mg/l), and benzyladenine (2.00 mg/l) in combination with kinetin (1.00 mg/l) was tested. The results show that the double coty-node explants produce the highest number of shoots per explant, an average of 7.93 shoots on Murashige and Skoog medium supplemented with 2.00 mg/l benzyladenine. The lowest number being 1.87 shoots obtained from single coty-node explants cultured on Murashige and Skoog medium containing 4.00 mg/l benzyladenine. The single coty-node explants showed lower frequency (10–57%) of shoot induction when compared to the double coty-node explants (50–83%). The suitability of aminoglycoside antibiotics (hygromycin, tetracycline and rifampicin) for efficient elimination of Agrobacterium tumefaciens after co-cultivation was tested using a well agar diffusion assay. Co-culturing double coty-node explants with Agrobacterium containing pTF 101 vector carrying the Oryza cystatin 1 gene resulted in 76.6, 63.3 and 60.0% shoot regeneration on Murashige and Skoog shoot induction media (shoot induction medium 1, shoot induction medium 2 and shoot induction medium 3) containing hygromycin, tetracycline and rifampicin at 500 mg/l respectively. These antibiotics showed the highest zones of inhibition against pTF 101 using the well agar diffusion assay. On the other hand, 85% plant regeneration was obtained during in vivo transformation following Agrobacterium injection into seedlings. These results imply that vi both in vitro and in vivo protocols were suitable for transgenic shoot regeneration and plant establishment since all the plants continued surviving in the presence of 6.00 mg/l glufosinate-ammonium. Future work will focus on screening of transgenic plants using beta-glucuronidase and isolating the protein encoded by the Oryza cystatin 1 gene to further confirm the generation of transformed plants carrying the gene of interest.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 130-144).

A combination of root morphology and plant physiology with drought/or salt tolerance should affect drought resistance in cotton (Gossypium hirsutum L.). This experiment was developed to evaluate early vegetative and seedling growth of cotton from the unselected parents with two selected populations of M-8844-0100, DPL 50, and TAM 94L-25 across two cycles for seedling drought. Three genotypes from three generations of selection were grown in tubes to evaluate early growth and in containers to evaluate seedlings for drought resistance in a greenhouse at College Station, TX in 2008 and 2009. The experiment during the winter months of 2008 resulted in shorter tap root length, fewer lateral roots, and lower fresh and dry weight for total root, lateral roots, and shoots. The drought selections in these genotypes affected the tap root fresh weight, and the number and weight of lateral roots. TAM 94L-25 averaged higher tap root fresh and dry weight, lateral root fresh weight and shoot fresh weight. DPL 50 exhibited greater weight of lateral roots and shoot fresh weight. No difference was found in percent wilting across generations for drought at 75 percent apparent wilting and recovery at 90 percent apparent wilting.

The mechanism of drought resistance in the seedlings of Aleppo pine (Pinus halepensis) and Brutia pine (Pinus brutia) was investigated. Both species showed anatomical and morphological adaptations to conserve moisture. Aleppo pine had a thicker cuticle, fewer stomata per unit length, per unit area, and per needle than Brutia pine. A significant number of Aleppo pine stomata were sealed with a waxy layer. Brutia pine had shorter needles, smaller needle surface area, a smaller surface area-to-volume ratio, and longer main root length. The two species were similar in height growth and in the seasonal trend of total non-structural carbohydrates (reducing sugars and starch). Brutia pine had more reducing sugars and less starch in its shoots than Aleppo pine. The latter had a greater amount of total non-structural carbohydrates and starch when the seedlings were subjected to dry down moisture stress. Electron microscopy techniques were used to monitor ultrastructural changes in the chloroplasts of mesophyll cells. Aleppo pine was found to contain chloroplasts exhibiting water stress-related damage at a relative water content of 62 percent, where as Brutia pine chloroplasts were disrupted. It is suggested that future investigations examine the physiological manifestation of drought mechanism at the cellular and molecular levels of both species.

Thesis (Ph.D. Agriculture (Soil Science)) -- University of Limpopo, 2017. / Climate change and variability pose a significant challenge to future global food security due to changes in mean climatic conditions which are rendering many areas marginally suitable for crop production. Erratic rains, drought, heat stress and declining soil fertility are some of the factors limiting crop productivity in many arid and semi-arid areas. Furthermore, water resources that could be used to mitigate drought and erratic rains, are also threatened by both scarcity and overuse. To ensure food security in the future, adaptation strategies at crop and management levels should be explored. Adaptation to future drier and warmer climates calls, among others, for improvement in drought resistance of crops through measures such as screening traits for drought tolerance and water use efficiency. This PhD study was carried out at University of Limpopo experimental farm, Limpopo Province, South Africa, a region with a semi-arid climate and mean annual rainfall of ca. 500 mm. The main aim of the study was to evaluate the use of plant δ13C and δ18O as screening traits for potential yield and water use efficiency of crop genotypes under drought conditions. The study also determined the agronomic performance of cowpea (Vigna unguiculata L. Walp.) and triticale (x. Triticosecale Wittmack) genotypes under varying soil moisture conditions including biological nitrogen fixation for cowpea. Both crops were grown under field conditions and the following four moisture levels (averages per level) were applied: well-watered (ca. 420 mm), moderately well-watered (ca. 350 mm), medium stress (ca. 290 mm), and severe stress (ca. 220 mm). The triticale experiment evaluated the agronomic performance and the spectral response of triticale to water stress under semi-arid conditions. The results showed a significant (P < 0.05) influence of moisture levels on the spectral reflectance, as well as on biomass and grain yield performance of triticale. However, these measured parameters did not significantly (P > 0.05) respond to genotypes probably due to the pre-screening of the genotypes or the lack of distinct genetic diversity in the studied parameters. Under well-watered conditions, triticale produced a grain yield of 3.9 t ha-1 in 2013 and 4.9 t ha-1 in 2014. These yields were however, found to be low when compared to other studies. Even though, no statistical differences were observed among the genotypes, Agbeacon showed a tendency of higher performance compared to the other genotypes. Of the four spectral indices tested, water based indices i.e. the water index (WI) and normalised difference water index (NDWI) were found to be more effective in detecting leaf water status compared to greenness based indices (normalised difference vegetation index and nitrogen reflectance index). This is because NDWI and WI respond to short term changes in water content of leaves. Overall, the performance of triticale showed a good adaptation to semi-arid conditions. The evaluation of δ13C and δ18O as screening traits for potential yield and water use efficiency under drought conditions produced interesting results. The findings showed that, Δ13C was positive and strongly related to grain yield and thus has potential to be used as a surrogate for grain yield in triticale under water stress. We also found a negative relationship between Δ13C and intrinsic water use efficiency (WUEintrinsic), which suggests that breeding for higher WUEintrinsic in triticale may not necessarily yield the desired improved grain yield. Measured grain Δ13C and flag leaf Δ13C suggested minimum contribution of pre-anthesis assimilates to grain filling under water stress, contrary to what is reported in literature. However, for concrete conclusions on the source of assimilates to the grains under drought conditions, further studies are still needed. Combining δ13C and δ18O provided more information on the physiological responses of triticale to varying moisture levels. The δ13C and δ18O were used to test the dual isotope model by Scheidegger et al 2000 and the results showed that, vapour pressure deficit (VPD) of air plays an important role in the operation of the model. The study indicated that the model worked only under high VPD when stomatal conductance limits transpiration rate but failed to work when VPD was relatively low and limiting transpiration rate. In order to address the declining soil fertility in the smallholder farming sector as well as the predicted loss in productivity of the commonly grown dry bean, this PhD study evaluated cowpea genotypes for biomass yield, grain yield and biological nitrogen fixation (BNF) under varying moisture levels. The results showed that soil moisture levels indeed affect biomass production, grain yield, nodule formation and the ability of cowpea to fix atmospheric nitrogen. BNF and nodule formation were the most sensitive to water stress compared to the other parameters. Severe water stress reduced BNF by 57% relative to well-watered conditions while nodule mass was reduced by 80% for the same soil moisture levels. Genotype TV4607 was superior in most of the parameters determined except for grain yield. As a result, TV4607 produced the highest biomass and returned the most nitrogen back to the soil compared to the other genotypes. However, IT00K-1263 emerged as the superior genotype due to its ability to produce the optimum balance of biomass, grain yield and BNF. Stomatal behaviour of cowpea under varying moisture levels was also investigated and the results showed sensitivity of stomatal conductance to soil moisture levels. As expected, stomatal conductance was high under well-watered conditions compared to water stressed conditions. Genotypic variation in stomatal conductance was only observed at early stages of cowpea growth i.e. at 47 and 54 days after planting (DAP). In conclusion, this PhD has shown that δ13C has potential to be used in breeding for drought resistance in triticale and probably other small grain crops. This study also revealed that there is minimum contribution of pre-anthesis assimilates to grain filling under water stress, contrary to what is reported in literature and hence more research is needed.The evaluated genotypes of triticale and cowpea showed tolerance to drought stress under semi-arid conditions. Agbeacon for triticale and IT00K-1263 for cowpea were identified as the most promising genotypes and hence their adoption in the smallholder farming system could be a step towards adapting to future warmer and drier climates

Drought is one of the most severe natural disasters and detrimentally impacts water resources, agricultural production, the environment, and the economy. Climate change is expected to influence the frequency and severity of extreme droughts. This dissertation evaluates drought conditions using a variety of hydrologic modeling approaches include short-term drought forecasting, long-term drought projection, and a coupled surface-groundwater dynamic drought assessment. The economic impacts of drought are also explored through a linked economic impact model. Study results highlight the need for various drought assessment approaches and provide insights into the array of tools and techniques that can be employed to generate decision-support tools for drought mitigation plans and water resource allocation. For short-term drought forecasting, the Soil and Water Assessment Tool (SWAT) and Variable Infiltration Capacity (VIC) models are used with a meteorological forecasting dataset. Results indicate that eight weeks of lead-time drought forecasting show good drought predictability for the Contiguous United States (CONUS). For the drought projection at a finer scale, both SWAT and VIC models are applied with Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model outputs to derive multiple drought indices for the Chesapeake Bay watershed and five river basins in Virginia. The results indicate that current climate change projections will lead to increased drought in the entire Chesapeake Bay watershed and Virginia river basins because of increases in the sum of evapotranspiration, and surface and groundwater discharge. The impacts of climate change on future agricultural droughts and associated economy-wide implications are then evaluated using the VIC and IMPLAN (IMpact analysis for PLANning) model for the several congressional districts in Virginia. The result indicated that increases in agricultural drought in the future would lead to decreases in agricultural productions and job losses. Finally, a coupled framework using the VIC and MODFLOW models is implemented for the Chesapeake Bay and the Northern Atlantic Coastal Plain aquifer system, and the results of a drought index that incorporates groundwater conditions performs better for some drought periods. Hydrologic modeling framework with multiple hydrologic models and various scales can provide a better understanding of drought assessments because the comparisons and contrasts of diverse methods are available. / PHD / Drought is one of the most severe natural hazards and negatively impacts the water resources, agricultural production, the environment, and the economy. Climate change influences the frequency and severity of extreme droughts. This dissertation assesses drought conditions using various hydrologic-modeling methods, which are drought forecasting, climate change impacts on drought, economic influences of droughts, and a coupled model approach. Study results highlight the need for various drought evaluation techniques that can generate decision-support tools for drought mitigation plans and water resource management. For short-term drought forecasting, two hydrologic models are used with a meteorological forecasting dataset. Results indicate that eight weeks of lead-time drought forecasting show good drought predictability for the Contiguous United States (CONUS). For the drought projection at a finer scale, two models are also used with multiple climate models for the Chesapeake Bay (CB) watershed and five river basins in Virginia. The results indicate that current climate change projections will lead to increased drought in the entire CB watershed and Virginia river basins. The impacts of climate change on future agricultural droughts and associated economy-wide implications are then evaluated using the hydrologic and economic models for the several congressional districts in Virginia. The results indicate that increases in agricultural drought in the future would lead to decreases in agricultural productions and job losses. Finally, a coupled model is implemented for the CB and the Northern Atlantic Coastal Plain (NACP) aquifer system, and the results of a drought index that incorporate groundwater conditions performs better for some drought periods. Hydrologic modeling framework with multiple hydrologic models and various scales can provide a better understanding of drought assessments because the comparisons and contrasts of diverse methods are available.

LD2668 .T4 1942 M42 / Master of Science

Master of Science / Department of Agronomy / Kraig L. Roozeboom / Due to decreased availability of irrigation water in central and western Kansas and an increase in water restrictions, producers are looking for more efficient ways to use available irrigation water. Drought-tolerant technologies have become popular in hybrids for stress-prone environments across central and western Kansas and are marketed for their ability to produce greater grain yields with less water. The objective of this research was to understand how DT and non-DT corn hybrids respond in a wide range of environmental conditions in terms of soil water status change, canopy indicators of stress, dry matter partitioning, and grain yield. Soil water status change, yield, and canopy response characteristics of two DT hybrids, and one non-DT hybrid were compared at five locations over two years in rain-fed, semi-irrigated, or fully irrigated regimes making a total of 18 environments. Field experiments were established in 2014 and 2015 near Topeka, Scandia, Hutchinson, Garden City, and Tribune, KS. Two corn hybrids with different approaches drought tolerance (Pioneer 1151 AQUAmax, bred drought tolerance and Croplan 6000 DroughtGard, bred drought tolerance plus transgenic drought tolerance), and one hybrid with no specific drought tolerance characteristics but with proven performance in favorable environments (Croplan 6274) were used in the experiment. Soil moisture content (measured using a neutron moisture meter), canopy temperature, ear leaf temperature, and chlorophyll content were measured at tasseling (VT), milk or dough (R3-R4), and physiological maturity (R6) developmental stages. Grain yield was at all 18 environments, and biomass production was estimated at 14 of the environments. Hybrid plasticity of yield results show the response for Croplan 6000DG and Pioneer 1151AM differed, but Croplan 6274 was the same as both other hybrids at the 0.10 alpha level. Yields of all hybrids remained comparable in most environments, but as environment yields increased beyond 200 bu acˉ¹, Croplan 6000DG lagged behind Pioneer 1151AM. Hybrid harvest index plasticity shoed that all hybrids had the same response to environment in harvest index. Although, not statistically significant, when an environment supported favorable harvest index values greater than 0.40, it’s observed that Croplan 6000DG does have an improvement in harvest index relative to the Pioneer 1151AM and Croplan 6274.

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