Thesis submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfillment of the requirements for the degree PhD Science Johannesburg, September 2014 / Drought has the potential to reset trophic interactions within natural and managed ecosystems. I tested how drought stress in maize and companion plants that are used in cereal agroecosystems of Kenya affect oviposition preference, larval feeding, and development of the spotted stemborer, Chilo partellus Swinhoe (Lepidoptera: Crambidae). Five host species were tested (all Poaceae): maize (Zea mays L.), Napier grass (Pennisetum purpureum Schumach), signal grass [Brachiaria brizantha (A. Rich) Stapf], Brachiaria cv ‘Mulato’, and molasses grass [Melinis minutiflora (Beauv.)]. Under periods of water deficit, maize was oviposited on as much as under control unstressed maize in both choice and no-choice experiments. Similarly, larval leaf damage was not significantly different in drought-stressed and unstressed maize. However in Napier and signal grasses, oviposition occurred less on drought-stressed than on unstressed corresponding individuals of the same species. Oviposition acceptance and foliar damage remained low in both drought-stressed and unstressed molasses grass and Mulato. Larval survival and development remained high in drought-stressed maize, but not in Napier, signal, and molasses grass and Mulato, where survival and development were low in both drought-stressed and unstressed plants. Drought stress resulted in increased total plant volatile emission in Napier and signal grasses. This significant change in total volatile emission of the plants upon stress was not present in molasses grass, Mulato II, Silverleaf and Greenleaf Desmodium despite variable changes in the quantities and qualities of particular constituent compounds among all the plant species during water deficit. In wind tunnel bioassays, volatile organic compounds (VOCs) from irrigated Napier and signal grasses were more attractive to C. partellus than the treatment plants. However, volatiles from molasses grass, Mulato II, Silverleaf and Greenleaf Desmodium were never preferred by the gravid moths in both irrigated and drought stressed v conditions. These changes in chemical constituents of the plant VOCs also elicited behavioural responses in parasitoids. Drought-stressed Napier grass attracted gravid Cotesia sesamiae parasitoids. Other companion plant species such as molasses grass and Mulato which constitutively emit these terpenes remained attractive to the parasitoids even under periods of drought. I attribute this differential preference of the moths to the constitutive and/or induced emission of key terpenoid compounds in plants that were tested. The induction of terpenoid compounds was coupled with a reduction in the amount of green leaf volatiles such as (Z)-3-hexenyl acetate in Napier and signal grasses. Taken together, the results suggest that control of stemborer pests using stimulo-deterrent diversion tactics remains possible under periods of environmental change.

Thesis (Ph. D.)--School of Computing and Engineering and Dept. of Mathematics. University of Missouri--Kansas City, 2005. / "A dissertation in engineering and mathematics." Advisor: Bryan R. Becker. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed June 26, 2006. Includes bibliographical references (leaves 133-134). Online version of the print edition.

Call number: LD2668 .T4 1948 W4 / Master of Science

Call number: LD2668 .T4 1978 B35 / Master of Science

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 226-231). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 226-231). Also available on the Internet.

Thesis (M.Sc. (Agronomy)) -- University of Limpopo, 2019 / Smallholder farmers are usually confronted with severe climatic conditions during summer growing seasons on production fields that are generally characterized by poor soil fertility and consequent low crop yields. Conservation agriculture could be a feasible local practice under such conditions to ensure a more sustainable and environmentally friendly system for cultivating crops. A rainfed field experiment was conducted at two diverse agroecological sites, Syferkuil and Ofcolaco during 2017 growing season in the Limpopo Province of South Africa to evaluate production, and symbiotic activities in soybean (Glycine max (L.) Merrill) and also to validate the performance of the Agricultural Production System Simulator (APSIM) model in simulating soybean biomass accumulation and grain yield under tillage and mulch practices. The experiment was established as a randomized complete block design in a split-plot arrangement with tillage (till and no-till) as the main plot treatment and four rates of grass mulch (0, 3, 6 and 9 tons ha-1) as the sub-plots treatment. The APSIMSoybean model was used to validate the result for simulated biomass and grain yield for the tillage practices at different mulching rates. A greenhouse experiment was also conducted during the 2017/2018 growing season to enhance the understanding of undulation potential in the selected soybean cultivar together with other cultivars. The greenhouse experiment was laid out in a randomized complete block design (RCBD) with four replications. Three soybean cultivars, commercial cultivar Donmario 8.6IRR (sourced from Agricol), Dundee commercial cultivar and Ibis 2000 (both sourced from Agricultural Research Council) were evaluated for their growth, phenological development, and symbiotic activities. Soybean growth was significantly (p≤0.001) affected by tillage at Syferkuil but not at Ofcolaco with the tilled soil having more pronounced growth than no-till at the former. Addition of mulch resulted in improved soybean growth relative to the control at both localities. Tillage and mulch as well as their interactive effects on soil moisture was significant at Syferkuil. Across tillage practices mulch application exhibited the highest moisture content than the control plots. At Ofcolaco tillage and mulch significantly (p≤0.001) affected soil water content but not the interaction effect, with more moisture recorded under the no-tilled condition and mulch application rate of 9 t ha-1 Soybean shoot and root nitrogen content was not influenced by tillage but was responsive (p≤0.001) to mulch application at both sites. The application of 9 t ha-1 mulch increased the shoot nitrogen content compared to the control plants at both locations. Soybean biomass and grain yield were also significantly influenced by tillage and mulch at Syferkuil but not at Ofcolaco (p≤0.001). A significant interaction effect of tillage and mulch (p≤0.001) on biomass and grain yield was also observed at Syferkuil but not Ofcolaco. At Syferkuil, higher biomass and grain yield was observed under the tilled condition when mulch at the rates of 6 and 9 tons were applied whereas, at Ofcolaco, soybean biomass and grain yield was higher under mulch application than the control with mulch application of 9 tons ha-1 at this location having the highest biomass and grain yield. The results of the APSIM model simulation showed the simulated biomass and grain yield to have a positive relationship. Hence, APSIM model can be used to guide alternate management practices to improve soybean production in the Limpopo Province. Findings from the greenhouse trial revealed that soybean cultivars significantly (p≤0.001) vary in symbiotic activities, growth, and physiological development. Across the cultivars, Ibis 2000 was superior in all studied parameters whereas Donmario, the cultivar used in the field trial was generally inferior among the three. KEYWORDS: Cultivars, Grain yield, Soybean, / Department of Science and Technology (DST) and National Research Foundation (NRF)

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Call number: LD2668 .T4 1985 M377 / Master of Science

Call number: LD2668 .T4 1985 W8 / Master of Science