Thesis(Ph.D.(Botany)) --University of Limpopo,2019 / Genetic transformation offers great opportunities for rapidly introducing, selecting or inducing desired characteristics in various leguminous plants for breeding purposes. But, this technique remains aloof for soybean improvement due to challenges such as genotype specificity, inefficient regeneration protocols and the rapid loss of viability in seeds required to develop explants. However, the rate of seed deterioration and its influence on in-vitro plant genetic transformation differs according to the age, storage duration and moisture content of the seeds used. The moisture status of the seeds is usually high during harvesting and deterioration (loss of viability) starts to occur when seeds are stored under ambient conditions for long periods. This seed deterioration also results in a phenomenon called “recalcitrance”, which is predominantly realised in soybean. In the present study, selected soybean genotypes were analysed for: (i) the efficiency of germination using seeds stored for 0, 3, 6 and 9-months under ambient conditions (ii) the effect of seed storage on in-vitro multiple shoot induction, (iii) the competency of the selected soybean genotypes on callus induction and Agrobacterium-mediated genetic transformation and (iv) the evaluation of protein profiles of the genotypes following co-cultivation of cotyledonary node explants with A. tumefaciens. The results obtained in this study showed that, seed stored for more than 3-months had reduced rates of germination, seedling development and in-vitro shoot multiplication. In particular, seed stored for 9-months showed a significant drop in seed germination, and less than 50% overall seed germination (Dundee-42%, LS678- 49%, TGx140-2F-44% and TGx1835-10E-48%) except for LS677 and Peking with 52 and 55%, respectively. The efficiency of multiple shoot induction also decreased with the prolonged seed storage, with all genotypes recording overall decline from about 96% to 40% regeneration efficiency over this period. The mean number of induced shoots decreased from more than 10.5 to 4.2 shoots per explant, for each genotype. The results obtained clearly indicated that efficient in-vitro shoot induction depended largely on seed storage duration, viability and significantly differed according to genotype. Following the evaluation for callus induction and Agrobacterium-mediated genetic transformation frequencies, the results indicated that the responses were genotype specific. This trend was consecutively observed in all soybean cultivars used (LS677, LS678, Dundee, Peking, TGx1740-2F and TGx1835-10E). Furthermore, the responses of the genotypes were also dependent on the culture media composition,especially, plant growth regulators and antibiotics. Amongst the cultivars used, Peking demonstrated the highest callus induction capacity (more than 70%) on MS-A and the mean number of shoots induced (1.65) using cotyledonary explants co-cultivated with Agrobacterium. This was followed by LS677 (1.42 shoots), LS678 (1.40 shoots), Dundee (1.30 shoots), TGx1835-10E (0.80 shoots) and TGx1740-2F (0.75 shoots), respectively. These genotypes also demonstrated low yields of proteins, extracted using a TCA buffer, and separated by means of two-dimensional polyacrylamide gel electrophoresis. The one-dimensional and two-dimensional profiles of proteins extracted from explants infected with Agrobacterium differed significantly to those expressed without co-cultivation of cotyledonary nodes with bacteria. These observations suggested that, the infection and co-cultivation of explants with Agrobacterium may have caused the expression of new proteins. Newly expressed proteins could also be found to either promote or inhibit transgene integration and expression on the cotyledonary node explants transformed with Agrobacterium tumefaciens for trait improvement. This study has clearly demonstrated that soybean production is confronted with a myriad of stress factors, including seed storage and quality problems due to unfavourable storage duration and weather conditions, amongst others. Thus, soybean seeds used for germination, callus induction, multiple shoot induction and genetic improvement should be harvested at R8 stage after reaching physiological maturity (with 20-35% seed moisture content) to avoid any mechanical damage, shattering or loss of seed viability. / National Research Foundation

No description available.

Heterodera glycines, soybean cyst nematode (SCN) causes more than one billion dollars soyben production loss in the U.S. annually. SCN is an obligate parasite of specialized feeding cells within the host root known as syncytium. The SCN resistance genes and signaling pathways in soybean have not been fully characterized. Gene expression analysis in syncytium from compatible and incompatible interactions identified candidate genes that might involve conferring resistance to SCN. This dissertation aimed to investigate the biological functions of the candidate resistance genes to confirm the roles of these genes in resistance to SCN. The study demonstrated a role of syntaxin 31-like genes (Gm-SYP38) in resistance to SCN. Overexpression of Gm-SYP38 induced the transcriptional activity of the cytoplasmic receptor-like kinase BOTRYTIS INDUCED KINASE 1 (Gm-BIK1-6). Overexpression of Gm-BIK1-6 rescued the resistant phenotype. In contrast, Gm-BIK1-6 RNAi increased parasitism. In another experiment, the expression of a Glycine max homolog of LESION SIMULATING DISEASE1 (LSD1) resulted in the transcriptional activation of ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) and NONEXPRESSOR OF PR1 (NPR1), that function in salicylic acid (SA) signaling, implicating the involvement of the antiapoptotic, environmental response gene LESION SIMULATING DISEASE1 (LSD1) in defense that is demonstrated here. The study also investigated the role of SNARE components (genes functioning in membrane fusion) in resistance to SCN. Experiments showed that SNARE functions in concert with a beta-glucosidase having homology to PEN2 and an ATP binding cassette transporter having homology to PEN3. This study provides novel information for the genetic improvement of soybean for enhanced disease resistance.

No description available.

No description available.

Fusarium virguliforme is a soil-borne pathogen that is the causal agent of sudden death syndrome (SDS). This disease is one of the top contributors to major yield losses in soybean across the United States. Characteristic symptoms of the disease include interveinal chlorosis and/or necrosis of trifoliate leaves and defoliation. In some cases, the foliar symptoms may not be present, but yield loss still occurs. This disease is evaluated using an incidence rating, the percent of plants in the plot that are expressing symptoms, and a severity rating, using a one to nine scale based on varying levels of chlorosis, necrosis, and defoliation. Using remote sensing provides an alternate approach to identify and evaluate plant diseases. It provides a non-destructive method to assess the severity of foliar symptoms and their distribution across production fields. SDS was chosen as the disease to use for this system due to the unique disease symptomology and yield loss. In 2019 and 2020, SDS trials were established in a production field location that has a history of SDS in Valmeyer, IL. This seed treatment study had different chemicals with varying levels of efficacy against SDS. Disease ratings were collected at the first sign of symptoms, and aerial imagery was collected on the same day. There were multiple dates across both years when this data was collected. ArcGIS was used to analyze the multispectral imagery and do a plot by plot analysis for each of the plots. A regression analysis was performed to test the relationship between the foliar disease ratings and the plot data collected from the multispectral imagery. Multiple vegetation indices were tested, and the results showed that overall, in 2019, GNDVI had the strongest relationship with foliar ratings. In 2020, NDRE had the strongest overall relationship with foliar ratings. The relationship between NDVI and the ratings was the most consistent at the last rating of the season.

Soybean growers in the mid-southern U.S. face many challenges imposed by adverse weather conditions that vary spatially and temporally. As a result, growers experience variations in soybean seed quality, grain quality, and yield. While not every harvest season experiences extremes in environmental conditions, those that do may result in major quality issues that could lead to significant financial losses. Therefore, the objective of this research was to evaluate quality as it relates to delayed harvest conditions for soybean following common management practices such as fungicide application to mitigate spread of pathogens or harvest aid application to facilitate more efficient harvest. Experiments were conducted in 2019 and 2020 to determine the impact that these soybean management practices have on soybean quality under delayed harvest conditions. Results indicate that soybean quality, regardless of planting date, was not impacted by fungicide or harvest aid treatment, but rather by harvest delay.

The responses of soybean (Glycine max (L.) Merr.) to soybean mosaic virus (SMV) include mosaic, necrosis and no symptoms, and vary with virus strain and allele of the gene for resistance (Rsv) carried by the host. Genetic studies have shown that plants giving mosaic are susceptible, and that plants giving either the necrotic or symptomless response are resistant. The objective of this study was to examine the mechanism of resistance by tracking SMV replication and movement in susceptible responses, and its restriction in necrotic and symptomless responses. Two SMV strains were inoculated at a single spot to Rsv-containing genotypes, selected to give each response. The leaf imprint immunoassay was developed and used to track the rate and extent of invasion by SMV from the tip of a primary, unifoliolate leaf to regions within that leaf and to the stem and younger trifoliolate leaves. In susceptible responses, SMV was detected at the site of inoculation in 6-7 days, and throughout the mid-rib and in the first trifoliate leaf in 8-9 days. In necrotic resistance responses, SMV was detected at and around the inoculation site in 8-9 days and in leaf veins, midrib and the first trifoliolate in 15-17 days, but was restricted to necrotic areas. In symptomless resistance responses, no virus was detected at any time. Greater virus replication and movement was found in unifoliolate and trifoliolate leaves of younger (15 days-old) than of older (18-days-old) plants. It was concluded that: (i) necrotic ally-responding cultivars manifest resistance by reduction and delay in replication, and by restriction of virus movement; (ii) virus replication is restricted in resistant cultivars; and (iii) rate and extent virus replication and movement is affected by stage of plant development. / Master of Science

The object of this investigation was to ripen and dry soybeans in such a way as to prevent the formation of bad taste and odor in the oil. Field run soybeans were treated in specially constructed gas-tight silos through which mixtures of air, carbon dioxide, and ethylene in varying concentrations were recirculated for the purpose of maturing and stabilizing the beans and to prevent peroxidases action, the latter being credited with imparting the offensive odor and taste to the oil and meal obtained by processing the bean. Nine silos were run simultaneously with nine different mixes of gases varying between 90 to 35% ethylene and 10 to 65% carbon dioxide and air. Whole beans were treated for 24 and 48 hours at 24, 37, and 50°C., rolled flat in a roll mill and expressed at 45-60°C. in a Carver hydraulic press at 10,000 lb. per sq. inch. From each sample of beans pressed was taken two samples of oil. One sample was left exposed to the air while the other one was sealed by means of a cap. From the taste and odor tests it was found that whole beans treated with ethylene at 24°C. Gave the best oil, being only slightly better than the oil from the whole beans treated at 37°C. Soybeans, when treated with ethylene and carbon dioxide, absorb varying amounts of the gases, depending on the gas concentration and the water removed. The drying rate of the soybeans by air was considerably less than the drying rate when ethylene and carbon dioxide were used. / Master of Science

no abstract provided by author / Master of Science