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Bacillus thuringiensis (Bt) is a gram-positive common soil bacterium that produces crystals (Cry) containing proteins that are toxic to certain insects, in particular larvae of Lepidoptera and Diptera. The Bt toxin in the past has been widely used as a bioactive compound for the biological control of mainly lepidopteran pests. Most recently a variety of crops, including cotton and maize, have been genetically modified to express a Bt toxin to confer resistance to lepidopteran pests. However, the effect of abiotic environmental stress, such as drought and heat, which are typical for Africa, on Bt toxin expression in a genetically modified crop has so far not been fully evaluated. This study focuses on the expression and stability of the Cry1Ac insecticidal protein from Bacillus thuringiensis in genetically modified cotton plants under drought and heat stress. These include the physiological and biochemical characterization of the expressed Bt toxin gene under drought stress as well as the biological activity against first-instar larvae of the African cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae). Non-genetically modified cotton (Gossypium hirsutum cv. Opal), as well as genetically modified cotton (cv. Nuopal) expressing the Bt toxin Cry1Ac, were exposed to drought and heat stress. Drought stress was induced by withholding watering plants until the soil moisture content reached 25- 30 % of field capacity. Non-stressed control plants were watered and soil moisture content to 80-100 % of field capacity was maintained. For heat stress, plants were grown at 38 to 32 DC during the day and night, respectively, whereas control plants were grown in a growth cabinet at a 28/25 DC day/night cycle. For growth analysis plants were harvested every second week after planting. At each harvest, different parts of the plant were collected and their fresh and dry weight determined. For biochemical analysis and determining biological activity against first-instar larvae of H. armigera, two types of experiments were carried out, the first experiment four weeks after treatment induction and the second experiment eight weeks after treatment induction. Different plant material (leaves, flowers and immature green bolls) were used for Bt detection as well as for determining biological activity against first-instar larvae of H. armigera. Under drought stress conditions a reduction in leaf area and leaf dry weight were found in both Bt toxin expressing and non-expressing cotton plants, but no significant difference in physiological performance between Bt-expressing and non-expressing cotton plants was found. This study shows that the Bt toxin (Cry1Ac) level decreases in senescent plants and that drought stress did not affect the growth and development of genetically modified Bt plants when compared to non-Bt plants. Although the expression of Bt toxin (Cry1Ac) in Bt cotton plants decreased under drought stress no effect on the efficacy of the toxin against H. armigera was observed. In addition, no significant decrease of Bt toxin content was found in Bt cotton leaves after exposure to heat stress when compared to leaves from nonheat stressed plants. / Dissertation (MSc)--University of Pretoria, 2008. / Plant Science / unrestricted

Submitted by MARINA GOMES DA SILVA null (marinags@hotmail.com.br) on 2016-08-04T16:07:16Z No. of bitstreams: 1 Diss_Agro_05 (002).pdf: 2170011 bytes, checksum: f477b7dc180f664f409a6c5baf8897fb (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-08-09T14:18:34Z (GMT) No. of bitstreams: 1 silva_mg_me_jabo.pdf: 2170011 bytes, checksum: f477b7dc180f664f409a6c5baf8897fb (MD5) / Made available in DSpace on 2016-08-09T14:18:34Z (GMT). No. of bitstreams: 1 silva_mg_me_jabo.pdf: 2170011 bytes, checksum: f477b7dc180f664f409a6c5baf8897fb (MD5) Previous issue date: 2016-07-06 / Atualmente, insetos praga estão impactando a produção de soja e táticas de controle não estão sendo eficientes, por causa do uso inadequado no campo. Assim opções para manejo de pragas precisam ser desenvolvidas, tais como novos compostos químicos. Devido a disponibilidade de formulação recentemente desenvolvida (concentrado emulsionável – EC) de indoxacarbe, os objetivos com este estudo foram avaliar a eficiência desta formulação no controle de Helicoverpa armigera (Hübner) e Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae) em soja. Um experimento a campo foi conduzido usando duas formulações (EC e solução concentrada – SC) de indoxacarbe (30 e 60 g i.a. ha-1) e testemunha. Após a pulverização, folíolos foram coletados das regiões mediana e superior das plantas em diferentes períodos. Os folíolos foram infestados com lagartas de 3°. instar de H. armigera e C. includens. As duas formulações do indoxacarbe foram eficientes no controle de ambas as pragas, independente da região da planta. As maiores dosagens causaram mortalidade > 80% em H. armigera somente 1h após a aplicação e em C. includens até 3 dias. No experimento de laboratório, folíolos recém-coletados de soja cultivada em casa-de-vegetação e imersos em soluções com concentrações crescentes das duas formulações de indoxacarbe para construção das curvas dose-resposta. Após secagem, os folíolos foram infestados com lagartas de 3°. instar de H. armigera e C. includens. As curvas dose-resposta foram similares para ambas as formulações. Para a espécie H. armigera, as formulações EC e SC de indoxacarbe apresentaram CL50 de 0,113 e 0,111 µg i.a. mL-1, enquanto que para a espécie C. includens, elas apresentaram CL50 de 0,065 e 0,127 µg i.a. mL-1, respectivamente. Para avaliar movimento translaminar de indoxacarbe, folíolos de soja foram tratados com as duas formulações de indoxacarbe (30 e 60 g i.a. ha-1) e foram então infestados com lagartas neonatas de C. includens. As formulações do indoxacarbe não apresentaram ação translaminar. A espécie C. includens mostrou ser mais sensível ao indoxacarbe do que H. armigera. De modo geral, a formulação EC é tão eficaz quanto a formulação SC no controle de H. armigera e C. includens em soja e pode ser utilizada como ferramenta no Manejo Integrado de Pragas. / Currently, insect pests are impacting soybean yield and control tactics are not efficient because of their inappropriate use in the field. Therefore, options for pest management ought to be developed, such as new chemical compounds. Because of the availability of recent developed formulation (emulsifiable concentrate - EC) of indoxacarb, the objectives of this study were to evaluate the effectiveness of this formulation for the control of Helicoverpa armigera (Hübner) and Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae) in soybean. A field experiment was carried out using two formulations (EC and suspension concentrate - SC) of indoxacarb (30 and 60 g a.i. ha-1) and an untreated control. After spray, leaflets were collected from mid and upper regions of the plants at different times. The leaflets were infested with 3rd instar larvae of H. armigera and C. includens. The two indoxacarb formulations were effective in controlling both species, regardless of plant region. Higher doses caused > 80% mortality of H. armigera only 1h after application and of C. includens up to 3 days. In a lab experiment, fresh soybean leaflets were collected from greenhouse and immersed in solutions with increasing concentrations of the two indoxacarb formulations to build the dose-response curves. After drying, they were infested with 3rd instar larvae of H. armigera and C. includens. The dose-response curves were similar for both formulations. For H. armigera, the EC and SC indoxacarb formulations showed LC50 of 0.113 and 0.111 µg a.i. mL-1 while for C. includens, they showed LC50 of 0.065 and 0.127 µg a.i. mL-1, respectively. To evaluate translaminar movement of indoxacarb, soybean leaflets were treated with both indoxacarb formulations (30 and 60 g a.i. ha-1) and were then infested with neonate larvae C. includens. No translaminar movement was detected. The species C. includens was more sensitive to indoxacarb than H. armigera. Overall, the EC formulation is as effective as the SC formulation for the control of H. armigera and C. includes on soybean and can be used as a tool in Integrated Pest Management.