<p>  </p> <p>Since the commercialization of dicamba-resistant soybean and cotton, numerous instances of suspected off-target dicamba movement onto sensitive plant species have been reported. Further investigation into chemical and environmental factors that influence dicamba volatilization is warranted to better understand the mechanisms that lead to increased dicamba off-target movement via volatilization and plant response to dicamba vapor. The environmental impacts of dicamba must be minimized in order to ensure the sustainability and continued use of dicamba, which is an important herbicide for controlling broadleaf weeds in key cropping systems and non-crop sites. </p> <p>Controlled environment experiments were conducted to characterize the chemical interactions with dicamba volatility for three formulations of dicamba on glass slides. Dicamba volatility was similar for spray solution pH levels 4 to 8 for the diglycolamine (DGA) and the diglycolamine with VaporGrip® (DGA+VG) formulations. For the N,N-Bis-(3- aminpropyl) methylamine (BAPMA) formulation, dicamba volatility increased at a pH level of 5 with continued increases in volatility occurring as spray solution continued to decrease indicating that BAPMA formulation is more sensitive to pH fluctuations than the DGA and the DGA+VG formulations. While spray solution pH levels below 4 increased dicamba volatility for all three formulations compared to each formulation applied at a native pH level (5.53, 5.2, and 6.28 for the DGA, DGA+VG, and BAPMA formulations, respectively), the largest increase in dicamba volatility occurred when ammonium or iron was added to spray solution. Therefore, applicators should avoid mixing dicamba with other tank-mix partners that contain ammonium or iron to minimize the likelihood for dicamba volatilization. </p> <p>While extensive research exists documenting the process of dicamba volatilization, there has been little confirmation regarding how volatilized dicamba enters sensitive plants. Dicamba-sensitive (DS) soybean with different levels of canopy conductance, from different watering regimes and exposure time of day, were exposed to dicamba vapor. The DS soybean response was positively correlated with soybean canopy conductance during the dicamba vapor exposure suggesting that dicamba vapor route of entry into soybean is facilitated through the stomata. An additional experiment was conducted that exposed the single side of a hypostomatic leaf to dicamba vapor on different northern red oak trees. Northern red oak tree response was substantially greater when the abaxial leaf surface (high stomatal density) was exposed to dicamba vapor compared to when the adaxial leaf surface (no stomata) was exposed to dicamba vapor. Thus, dicamba vapor entry into plants is largely facilitated via stomata and secondly through re-deposition onto the leaf surface, where dicamba is absorbed through the plant cuticle, albeit minor. If dicamba vapor is redeposited onto leaf surfaces, dicamba acid absorption through the cuticle can be limited without the presence of a surfactant. Field and greenhouse experiments confirmed that the presence of surfactants from applications of other formulated herbicides can exacerbate soybean response to dicamba acid that was deposited on the leaf surface. </p> <p>In the midwestern United States, off-target dicamba movement to DS soybean has been problematic as DS soybean are extremely sensitive to very low concentrations of dicamba. Field and greenhouses studies confirmed that there are phenotypic differences amongst different soybean genotypes and their response to dicamba. Estimations of visual soybean injury was approximately 10% less for genotypes that were less sensitive to dicamba compared to genotypes with increased sensitivity. The future identification of the mechanisms that lead to decreased sensitivity to dicamba could be used to identify soybean cultivars that could mitigate the impacts of dicamba off-target movement to DS soybean. </p> <p>Lastly, a field experiment was conducted that investigated the influence of simulated dew on dicamba volatility from dicamba treated soybean leaves, in addition to soybean response in the presence of dicamba vapor. The results from a field experiment determined that consecutive simulated dew applications increase dicamba volatility from dicamba treated soybean. Furthermore, this is the only research demonstrating that DS-soybean response increases from dicamba vapor in the presence of dew. The results from this dissertation provide further insight into the chemical and environmental factors that influence dicamba volatility, the route of entry of dicamba vapor into plants, and soybean response to dicamba.</p>

The objectives of this study were to determine the effects the temperature sensitivity of alleles of Rsv1 in soybean (Glycine max (L.) Merr.). Soybean cultivars carrying alleles of Rsv were exposed to 1 several heat treatments designed to induce heat shock protein production prior to inoculation with soybean mosaic virus (SMV). The heat treatment methods were similar to those employed in the research with N gene-tobacco mosaic virus studies. The soybean cultivars used were Lee 69, York, Kwanggyo, Ogden and PI96983, carrying the Rsv, Rsv1-y, Rsv1-k, Rsv1-t, and Rsv1 allles of Rsv1, respectively, and were selected to provide a range of reactions to selected SMV pathotype groups. For example Rsv1-y and Rsv1-k give a necrotic response to SMV G4 and SMV G6, respectively, while both are resistant to SMV G1. To determine the durability of resistance under heat shock conditions, the symptoms were observed for changes in the phenotype of the resistance response. Immunological techniques were employed to determine the vascular movement and localization of the viral antigen in the plant. Heat treatments used were found to induce HSP but to have no effect on the resistance phenotype. A detached leaf assay was used to test the same Rsv alleles at constant 1 high temperatures. Primary trifoliolate leaflets were removed and inoculated, then placed into a continuously lighted incubator at 20 °C or 30 °C. Leaf immunoprint assays were used to determine the localization of the viral antigen. The visible symptoms for necrotic lesions and veins were observed for necrotic phenotype-pathotype combinations but mosaic symptoms were not observed on detached leaves, as expected for inoculated leaves. The detached leaf assay confirmed that no change from the expected resistance response of the Rsv alleles occurred at 30 C. A breakdown 1 o of resistance to SMV at high temperature had been reported in soybean by Tu and Buzzell (1987). The resistance gene in which the high temperature breakdown occurred has been determined to be Rsv . Using cultivars and breeding lines carrying Rsv a similar experiment was attempted in growth 3 3 chambers. Preliminary results suggest that Rsv is temperature sensitive. / Master of Science

Soybean meal (SBM) is a staple proteinaceous feedstuff in diets for monogastric animals like poultry and swine. It is known that soybeans contain several anti-nutritional factors that, if untreated, results in decreased quality and bioavailability of amino acids (AA). Thermal processing via heat treatment of soybeans and SBM is essential for inactivation of these anti-nutritional factors; however, over-processing may result in extensive AA damage, particularly lysine. Feeding heat damaged SBM has been proven to be an inefficient source of AA for monogastrics as they cannot be used for any metabolic function. In typical corn-soybean meal diets for pigs and poultry, lysine is the first- and second- limiting AA, respectively. Currently, laboratory procedures are unable to accurately determine digestible lysine in SBM. The objective of this thesis was to compare SBM AA digestibility obtained from 28-day old broilers to values obtained from an in vitro digestion procedure. The correlation between AA concentration in the SBM and its in vivo standardized ileal digestibility (SID) was also analyzed. Twenty-four SBM samples (21 from U.S.A., 2 from Canada, and 1 from Mexico) were analyzed. In vivo lysine SID ranged from 69-93%. Results indicated no correlation (r = -0.16 to 0.21; P = 0.33 to 0.98) between analyzed AA content in SBM and in vivo SID. An increase in lysine SID was associated with an increase in the SID of phenylalanine, leucine, isoleucine, valine, tyrosine, alanine, threonine, glutamate, aspartate, methionine, histidine, and glycine (r² = 0.63 to 0.93; P < 0.001). Poor association was determined between lysine proline, arginine, and serine (r² = 0.14 to 0.43; P = 0.001 to 0.003). Lastly, results indicated no association (r² = 0.00 to 0.08; P = 0.17 to 0.99) between in vivo and in vitro SID for any of the AA tested. In summary, it appears that lysine may be a good indicator for SID estimations for most essential AA; however, SBM content of a particular AA is not a good indicator of its digestibility. Additionally, current in vitro digestibility techniques seemed inadequate in identifying in vivo SID differences and further analytical improvements are needed. / Master of Science

No description available.

Early planting soybean (Glycine max L.) strategies across the mid-southern United States has complicated weed management in the form of post-harvest weed control. Research has investigated the use of cover crops to aid in management of weed populations during winter months, but conventional cover crops provides minimal weed management benefit immediately following cash crop harvest. Inter-seeding cover crop into crop canopies has potential to promote earlier cover crop establishment, thus creating higher potential for post-harvest weed management. However, factors such as inter-seeding timing, herbicide residue, as well as harvest aid applications must be considered. Therefore, studies were conducted in Mississippi in 2017, 2018, and 2019 to determine if cover crops inter-seeded through soybean could improve weed control used in conjunction with common management strategies in Mississippi production systems. Conclusions drawn from these studies indicate inter-seeded cover crops can be utilized in soybean production systems to improve weed management after harvest.

No description available.

No description available.

Taproot decline (TRD), caused by an undescribed species of Xylaria, is an emerging root disease of soybean in Mississippi. Xylaria sp. isolates were collected from soybean roots and used to characterize TRD distribution as well as optimal growth temperature, pathogenicity, alternative host range, in vitro pathogenicity, and fungicide sensitivity. The 24 selected Xylaria sp. isolates from the 2016 collection had a mean optimal growth temperature of 26.7°C, and were pathogenic to soybean; however, differences in virulence occurred among isolates. Five selected Xylaria sp. isolates produced stroma on six hosts: corn, cotton, peanut, rice, sorghum, and wheat. Xylaria sp. colonized corn, cotton, and soybean seed in vitro; however, only reduced germination in soybean. Three selected Xylaria sp. isolates were exposed to fungicide-amended potato dextrose agar with concentrations up to 100 ppm of commercial products typically used in soybean production systems. Xylaria sp. isolates were insensitive to all active ingredients except thiophanate-methyl.

No description available.

No description available.