Doubled haploidy (DH) is a plant breeding technique that is often utilized by plant breeders to minimize the time required to reach homozygosity in breeding lines. The first objective of this study was to compare two methods of generating DH lines in tobacco (Nicotiana tabacum L.). Inbred burley tobacco varieties TN 90LC and GR 149LC were used to produce both androgenic derived doubled haploids (ADDH) and maternally derived doubled haploids (MDDH). The relative agronomic performance of TN 90LC and GR 149 LC ADDH and MDDH lines was compared when used either as pure-line cultivars or when used for the production of the KT 204LC and TN 97LC hybrid cultivars, respectively. The ADDH method was more efficient than the MDDH method in generating large numbers of haploid plants. On average the ADDH TN 90LC population was statistically inferior to the inbred TN 90LC for several agronomic traits; this inferiority of the ADDH method was not observed in the GR 149LC populations. For both genotypes, the MDDH populations were comparable to the inbred parental genotypes. The ADDH method was inferior for TN 90LC, but several individual TN 90LC ADDH lines were equal or superior to the inbred source. The agronomic variability observed in both ADDH and MDDH lines was decreased when they were used to produce hybrid cultivars. Less variation was observed in the DH-derived hybrids KT 204LC and TN 97LC compared to the ADDH and MDDH TN90LC and GR149LC parental lines, respectively. The significant inferiority of ADDH TN 90 lines in comparison to inbred TN 90LC was not observed in the ADDH derived KT 204 population compared to KT 204LC. The second objective of this study was to compare DH Lines derived from an F1 breeding population versus DH lines derived from a segregating F2 population where plants used for DH were pre-screened for quantitatively inherited resistance to soil-borne diseases black shank (Phytophthora nicotianae) and/or Fusarium wilt (Fusarium oxysporum f. nicotianae). There was a clear difference in susceptibility to black shank between the F1 and F2 derived DH populations, both in terms of average disease incidence, and more importantly, in the percentage of individual lines displaying high disease resistance. For two different burley crosses, DH lines derived from the F1 generation were considerably more susceptible to black shank than DH lines derived from the F2 generation. No differences in the incidence of Fusarium wilt were observed between DH lines of F1 and F2 generations; this was likely due to low overall disease incidence. Although delaying the DH process in tobacco from the F1 to the F2 generation could add time to the development of homozygous breeding lines, the delay may be offset by having to screen fewer finished DH lines to identify superior lines.

Kentucky is the nation’s leading producer of burley tobacco and the crop’s most economically important disease is black shank, caused by Phytophthora nicotianae (Pn). Current management is effective, however, problems with expense and pathogen persistence are issues. Two alternative methods for control of Pn were examined: biofumigation and soil application of an organic, yeast fermentation‐derived product (Soil‐Set). Field studies in 2009 and 2010 found no effect on populations of fungi, disease severity of Pn, and yield between mustard‐ and wheat‐amended plots. Experiments in the greenhouse suggested that survival of Pn was impacted by biomass rather than biofumigation. Biofumigation is not a viable option for controlling black shank in tobacco production. Soil‐Set was inhibitory against mycelial growth of Pn on corn meal agar rather than V8 juice. Results from a greenhouse study indicated that increasing the dose of Soil‐Set by four times what is recommended held the most potential for suppression of Pn in a burley variety with no resistance. A field study in 2012 found no differences among treatments in reducing severity of Pn in a variety with high resistance. More field and greenhouse studies need to be conducted to examine the potential of Soil‐Set in tobacco production.

Flue-cured tobacco (Nicotiana tabacum L.) is a high value-per-acre crop that is intensively managed to optimize the yield of high quality cured leaf. Aerial remote sensing, specifically unmanned aerial vehicles (UAVs), present flue-cured tobacco producers and researchers with a potential tool for scouting and crop management. A two-year study, conducted in Southside Virginia at the Southern Piedmont Agricultural Research and Extension Center and on commercial farms, assessed the potential of aerial remote sensing in flue-cured tobacco. The effort encompassed two key objectives. First, examine the use of the enhanced normalized difference vegetation index (ENDVI) for separating flue-cured tobacco varieties and nitrogen rates. Secondly, develop hyperspectral indices and/or machine learning classification models capable of detecting Phytophthora nicotianae (black shank) incidence in flue-cured tobacco. In 2017, UAV-acquired ENDVI surveys demonstrated the ability to consistently separate between flue-cured tobacco varieties and nitrogen rates from topping to harvest. In 2018, ENDVI revealed significant differences among N-rates as early as 34 days after transplanting. Two hyperspectral indices were developed to detect black shank incidence based on differences in the spectral profiles of asymptomatic flue-cured tobacco plants compared to those with black shank symptoms. Testing of the indices showed significant differences between the index values of healthy and symptomatic plants (alpha = 0.05). In addition, the indices were able to detect black shank symptoms pre-symptomatically (alpha = 0.09). Subspace linear discriminant analysis, a machine learning classification, was also used for prediction of black shank incidence with up to 85.7% classification accuracy. / Master of Science / Unmanned Aerial Vehicle’s (UAVs) or drones, as they are commonly referred to, may have potential as a tool in flue-cured tobacco research and production. UAVs combined with sensors and cameras provide the opportunity to gather a large amount of data on a particular crop, which may be useful in crop management. Given the intensive management of flue-cured tobacco, producers may benefit from extra insight on how to better assess threats to yield such as under-fertilization and disease pressure. A two-year study was conducted in Southside Virginia at the Southern Piedmont Agricultural Research and Extension Center and on commercial farms. There were two objectives to this effort. First, assess the ability of UAV-acquired multispectral near-infrared imagery to separate flue-cured tobacco varieties and nitrogen rates. Secondly, develop hyperspectral indices and machine learning models that can accurately predict the incidence of black shank in flue-cured tobacco. Flue-cured tobacco nitrogen rates were significantly different in 2017 from 59 days after transplanting to harvest using UAV-acquired near-infrared imagery. In 2018, heavy rainfall may have led to nitrogen leaching from the soil resulting in nitrogen rates being significantly different as early as 34 days after transplanting. The imagery also showed a significant relationship with variety maturation type in the late stages of crop development during ripening. Two hyperspectral indices were developed and one machine learning model was trained. Each had the ability to detect black shank incidence in fluecured tobacco pre-symptomatically, as well as separated black shank infested plants from healthy plants.