Doctor of Philosophy / Department of Entomology / Larry L. Buschman / C. Michael Smith / Several studies were conducted to develop soybean management options that could provide protection from the soybean stem borer, Dectes texanus LeConte. Selected soybean genotypes were screened for host plant resistance against D. texanus. Soybean plants were grown in a footprint that could be covered by a field cage. When beetles were flying in the fields they were collected and placed in the field cages to increase the insect feeding pressure on the test plants. A susceptible commercial soybean variety treated with the systemic insecticide fipronil was used as a positive antibiosis check. Both commercial soybean varieties and plant introductions (PIs) obtained from the USDA National Soybean Germplasm Collection in maturity groups (MG) VI to VIII were tested over a four-year period. Since the number of ovipositions per plant could not be controlled, the ratio of oviposition punctures (OP’s) per live larvae (OP/ Lv) was used as a novel index of potential plant antibiosis to D. texanus. Field evaluations identified PI165673 as a genotype with a very high OP/ Lv ratio - similar to that for the fipronil antibiosis control. PI165673 appears to be potential source of resistance to D. texanus. Factorial analysis indicated that soybean maturity group was not significant factor in the expression of resistance. The OP/ Lv ratio appears to be more sensitive means of identifying antibiosis than other more conventional damage indices. The use of field cages demonstrated consistent plant responses from year to year during the multi-year study. Greenhouse-grown soybean plants, including transgenic plants containing the Manduca sexta chitinase gene, were not morphologically appropriate for successful D. texanus oviposition because the greenhouse-grown plants were poorly developed and had not produced enough pith in petioles. Therefore the greenhouse results were inconclusive. Analysis of the vertical distribution of D. texanus oviposition on soybean plants revealed that D. texanus oviposition was most likely to occur on leaf petioles on the upper five nodes of the plant canopy. Histomorphological observations of plant petioles indicated that the proportion of the petiole perimeter occupied by vascular bundles might be related to D. texanus oviposition. Both foliar and seed applications of fipronil suppressed D. texanus larval damage on soybean plants. The efficacy of these treatments was sustained for long periods, even until adult beetles were present in early August. The effects of the fipronil seed-treatment and harvest date on grain yield were both significant while the interaction was not. A physiological yield loss of 8.2% and plant lodging losses of 2.9% were associated with D. texanus infestation.

Made available in DSpace on 2017-07-10T15:14:40Z (GMT). No. of bitstreams: 1 DissertacaoMaccariusCMoreira.pdf: 2771848 bytes, checksum: 12048a1e6cb70b03365efe6dd23ba0ac (MD5) Previous issue date: 2016-03-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The soil microbes quickly respond the changes that the management systems cause in the soil, therefore, are sensitive indicators of biological soil quality. In this context, this study aims to assess the impact of seven management systems (MI) Millet (glaucum Pennisetum), (AP) Oat (Avena strigosa), (MP) Black Mucuna (Stizolobium aterrimum), (EF) pea (pea subsp. arvense) + (AP) Oat (Avena strigosa), (PDG) Till plaster cast (PDE) Till scarified and (SPD) Planting Direct Traditionally, the soil quality bio-indicators, (TOC) Total organic carbon (MO) organic Matter soil, (CBMS) ground biomass carbon (RBS) basal soil respiration (qCO2) respiratory coefficient (qMIC), microbial coefficient (Ds) soil density and carbon and its effects on root growth and the yield of soybeans. It was used the completely randomized design, with seven treatments. Soil samples were carried out in three periods; (PP) pre-plant (PF) pre-flowering and (PP) after soybean harvest in the period from July 2014 to March 2015 in four replications for each analysis, and samples collected at Layer (0-10 ) from soil. Statistical analysis was performed using Assistat® 7.6 beta software, version 2012 (Smith, 2012). The analyzes were carried out analysis of variance (ANOVA) and treatment means were compared by TUKEY test at 5% significance; Black Mucuna, the pea forage and tillage system were the most suitable for the improvement of biological soil properties. The cover crops and management system does not affect the root growth and yield of soybean grain / A microbiota do solo responde rapidamente a alterações que os sistemas de manejo provocam no solo, por este motivo, são sensíveis indicadores da qualidade biológica do solo. Neste contexto, o presente trabalho tem por objetivo avaliar o impacto de sete sistemas de manejo, (MI) Milheto (Pennisetum glaucum), (AP) Aveia preta (Avena strigosa), (MP) Mucuna preta (Stizolobium aterrimum), (EF) Ervilha forrageira (Pisum sativum subesp. Arvense) + (AP) Aveia preta (Avena strigosa), (PDG) Plantio Direto Gessado, (PDE) Plantio Direto Escarificado e (SPD) Plantio Direto Tradicional, nos bioindicadores de qualidade do solo, (COT) Carbono orgânico total, (MO) Matéria Orgânica do solo, (CBMS) Carbono da biomassa do solo, (RBS) Respiração basal do solo, (qCO2) Coeficiente respiratório, (qMIC), Coeficiente microbiano, (Ds) Densidade do solo e Estoque de carbono e seus reflexos no crescimento radicular e no rendimento de grãos da soja. Foi utilizado o delineamento experimental inteiramente casualizado, com sete tratamentos. As amostragens de solo foram realizadas em três períodos; (PP) pré-plantio, (PF) pré-floração e (PP) pós-colheita da soja, no período de julho de 2014 a março de 2015, em quatro repetições para cada análise, e amostras coletadas na camada (0-10) do solo. A análise estatística foi realizada usando software Assistat® 7.6 beta, versão 2012 (Silva, 2012). As análises realizadas foram análise de variância (ANOVA) e as médias de tratamentos comparadas pelo teste de TUKEY a 5 % de significância. A Mucuna Preta, a Ervilha Forrageira e o Sistema Plantio Direto foram os mais indicados para a melhoria dos atributos biológicos do solo. As espécies de cobertura e os sistemas de manejo não interferiram no crescimento radicular e no rendimento de grãos da soja