Breeding for improved varieties that are in line with the market-preferred traits takes many years using traditional breeding methods. Methods that can accelerate the breeding process reduce the time required for cultivar development, release, and commercialization. This study evaluated the effect of tray cell size on the potential for using high-intensity light and etridiazole fungicide (Truban® 25% EC) application as a means of inducing early flowering response in tobacco seedlings for breeding purposes. Tobacco seedlings were grown in expanded polystyrene (Styrofoam) trays of 2 different sizes, which were floated on a solution of etridiazole 20 times the recommended rate of 0.0381 g/L, under high-intensity light (800 W, Fusion Bright 400 Super HPS high-pressure sodium bulb). The results revealed that the tray with larger cell volume, the 128-cell tray, allowed for improved plant growth due to a better root environment giving over 3.5 times more floral initiation and flowering as compared to the tray with small cell size, the 288-cell tray. The large cell tray also provided plants with the better outcome during subsequent seed production. The current study highlights the potential advantages of using this system in accelerated breeding for the successful development and release of pure line cultivars by allowing multiple generations to be achieved within 1 year.
Tennessee ranks second in the United States for the production of type 31 light air-cured burley tobacco ( Nicotiana tabacum L.), producing over 2,200 metric tons annually. Historical shifts in production have concentrated burley tobacco cultivation in the central region, alongside a notable decline in the number of farms and overall acreage. This study investigates the impact of harvest timing on yield, leaf quality, alkaloid content, tobacco-specific nitrosamines (TSNA), and residues of maleic hydrazide (MH) in burley tobacco. Conducted over two growing seasons at the Northeast Tennessee AgResearch and Education Center (NETREC), this research utilized a randomized complete block design with various harvest timings ranging from 2 to 6 weeks after topping (WAT). Results indicated that optimal total yield and leaf quality were achieved between 3 and 5 WAT, while harvests beyond this period risked overripeness and increased TSNA levels. Alkaloid accumulation, primarily nicotine, increased with longer harvest periods, but conversion to nornicotine remained stable due to the use of low-converter seed. Furthermore, MH residues were consistently below regulatory limits across all treatments, with higher concentrations observed in upper leaf positions. These findings reinforce existing recommendations for harvest timing, emphasizing the importance of balancing yield and leaf quality without detrimental impacts on TSNA accumulation and potential residue concerns in burley tobacco production. Future research should explore different maturity groups to further refine harvest timing.
ABSTRACT Field trials were conducted in 2021 at Princeton KY and in 2022 at Mayfield KY and Springfield TN to evaluate effects of fungicide programs on cigar wrapper leaf production in Connecticut Broadleaf cigar tobacco. Eleven fungicide programs were evaluated, including nine agrochemicals and two biological-based products. Applications began three weeks after transplanting and final applications occurred in the last week before harvest. There were significant treatment by location interactions, likely due to rainfall differences between the Princeton KY 2021 location and both locations in 2022. At Princeton KY in 2021, there were significant differences for total wrapper grades (sum of two-cut, binder, and wrapper leaves) produced. Tobacco treated with flutriafol produced higher wrapper yields than most of the other treatments. Fluopyram-treated tobacco also had significantly higher wrapper yield than tobacco treated with fluopicolide, oxathiapiprolin, or untreated tobacco. Tobacco treated with copper octanoate had higher wrapper yield than untreated tobacco. There were no significant differences in total yield, gross revenue, or total wrapper grades at either location in 2022. Based on 2021 results where significant differences were seen, flutriafol, fluopyram, and copper octanoate were most effective in increasing yield of wrapper grades.
Black shank, a soil-borne disease caused by Phytophthora nicotianae, is one of the most devastating oomycetes affecting dark tobacco worldwide. Field trials were conducted in 2018 and 2022 at an established black shank site near Hopkinsville, KY, to evaluate the efficacy of mefenoxam, fluopicolide, and oxathiapiprolin for management of black shank in dark fire-cured tobacco. Black shank field trials at this location have been conducted each year since 2006. KT D6LC, a dark-fired cultivar with moderate resistance to race 0 and race 1 black shank, was used in 2018 and 2022. Black shank infection was much greater in 2022, resulting in greater stand and yield loss in 2022 compared to 2018. Rainfall amount and timing differences between the 2 years likely contributed to these differences in final stand and yield. Final stand and total yield ranged from 80.7 to 99.3% and 2,374 to 2,882 kg ha−1, respectively, in 2018, and from 10.3 to 81.8% and 238 to 2,637 kg ha−1, respectively, in 2022. In both years, all oomyceticide treatments increased final stand and yield compared to untreated tobacco. In 2018, highest final stand came from tobacco that received mefenoxam or oxathiapiprolin plus mefenoxam at transplanting alone or followed by fluopicolide and mefenoxam after transplanting, or fluopicolide followed by mefenoxam after transplanting. Total yield was similar for tobacco treated with any oomyceticide treatment and higher than the yield of untreated tobacco in 2018. In 2022, tobacco treated with oxathiapiprolin plus mefenoxam in transplant water either alone or followed by fluopicolide and mefenoxam had significantly higher final stand and yield than all other treatments. Across both years, it was evident that oomyceticide applications made in transplant water, particularly oxathiapiprolin plus mefenoxam, had the greatest impact on black shank management in dark fire-cured tobacco.
In recent years, there has been increased demand for natural leaf cigar wrappers. The Connecticut River Valley has seen a decrease in production of cigar tobacco, causing tobacco dealers to seek other places to produce Connecticut Broadleaf cigar wrapper tobacco. Kentucky and Tennessee have been of recent interest as a new area for Connecticut Broadleaf production. Field trials were established in 2022 and 2023 at Mayfield, KY and Springfield, TN to evaluate effects of lower leaf removal on wrapper leaf production. Treatments included lower leaf removal at 4 levels (no leaf removal, leaf removal at layby, leaf removal at topping, or lower leaf removal at harvest) and fungicide treatment at 2 levels (fungicide application vs. no fungicide application). Lower leaf removal resulted in significant reductions in total yield and did not increase wrapper leaf grades at either location in either year. There were no significant differences observed in gross revenue due to lower leaf removal at the Mayfield KY location, however, phytotoxicity from azoxystrobin applications at topping resulted in significant decreases in wrapper leaf grades and gross revenue at Mayfield in 2023. Lower leaf removal also resulted in significant reductions in gross revenue at the Springfield, TN location in 2022. Based on these data, lower leaf removal would not be recommended as a means of increasing wrapper leaf production or revenue in Connecticut Broadleaf cigar wrapper tobacco grown in Kentucky or Tennessee.
Tobacco blue mold, caused by Peronospora tabacina , can quickly devastate cigar wrapper tobacco crops and must be managed with protectant fungicides. We conducted experiments with field-grown broadleaf wrapper and shade-grown Connecticut wrapper tobacco types to evaluate efficacy against blue mold and resulting fungicide residues in cured leaves. Fungicides were applied as weekly season-long programs versus front-loaded schedules where the same total amount of fungicide was applied but with higher rates early in the season. Efficacy against disease was evaluated, and leaves were harvested and cured. Fungicide residues were determined with the QuEChERS method. Blue mold was severe in the first year. Front-loading fungicides reduced disease and fungicide residues in broadleaf and shade tobacco. Blue mold did not occur in broadleaf in the second year, but front-loading fungicides and reducing rates again reduced fungicide residues in cured leaves. Blue mold occurred in only the second half of shade tobacco harvests, and disease severity was greater for front-loaded treatments, which coincided with reduced fungicide residues from those harvested leaves. Models were developed to describe the decline of dimethomorph, azoxystrobin, and mandipropamid to predict the time required since the last application to achieve target ppm residues in cured leaves. Target residues were achieved for broadleaf tobacco but not for shade-grown tobacco in these experiments.
Field trials were conducted in Princeton, Murray, and Lexington, KY in 2016–2018 to determine response of dark and burley tobacco to potassium source (potassium sulfate or potassium chloride) and potassium rate (0, 93, 186, or 279 kg K ha−1). Field sites that showed higher potential for potassium yield response were selected based on low soil test potassium levels from soil samples collected in early spring each year. All potassium applications were made between 1 and 10 days before transplanting. Significant yield responses to potassium were seen in 5 of 12 trials at sites that had initial soil test potassium levels of ≤150 kg K ha−1. Although cured leaf chloride levels were >1% on average where potassium chloride was used, negative effects on cured leaf moisture were only seen in 1 of 12 trials, and negative effects on quality grade index were not seen in any trial. The most consistent effect of potassium chloride application seen in this research was a 28% reduction in average total tobacco-specific nitrosamines (TSNA) compared to potassium sulfate application. These results showing lower TSNA from potassium chloride applications, along with minimal effects on moisture and quality grade index, may cause the tobacco industry to reconsider the long-standing preference for potassium sulfate as the potassium source for tobacco production.
Certified organic flue-cured tobacco (Nicotiana tabacum L.) production has experienced significant expansion in the United States. Despite this expansion, there is very little information available that outlines organic nitrogen (N) programs for seedling production. To develop grower recommendations, research was conducted to evaluate the effects of a Peruvian seabird guano (SG), sodium nitrate (SN), or a combination of the two (SN_SG) in a float system on float water chemistry and seedling vigor. A conventional treatment (Conv; SQM Ultrasol Premium) was included for comparison. A greenhouse study was conducted twice between June 2016 and January 2017. Nitrogen fertilizer treatments were applied to tobacco float system water twice during the germination and growth of tobacco transplants. Float system water was collected every 5 days and analyzed for N forms, pH, dissolved oxygen, and bicarbonate. At the end of each experiment, transplant dimensions were measured and percent of usable plants collected. Float water bicarbonate concentration was <1 meq L−1 in treatments absent of SG for the duration of the study, but were in excess of 12 meq L−1 25 days after seeding (DAS) when SG was the exclusive N source. Despite high ammonium and bicarbonate concentrations with SG, neither factor negatively impacted seedling growth. Both SG and SN_SG produced as many usable plants as Conv; however, seedling height and diameter tended to be lower in SG compared to the other two treatments. No usable transplants were produced when SN was the sole fertility source, likely because of lack of nutrients other than N. Furthermore, many of the organic fertility products require biological activity to mineralize organic N to a plant-available form. This activity can have potentially detrimental outcomes on float system solution pH, dissolved oxygen, and bicarbonate levels.
Field studies were conducted in North Carolina in 2010/2011 and 2012/2013 to determine the effect of flumetralin applied for sucker control in tobacco (Nicotiana tabacum L.) on sweet potato (Ipomoea batatas L. Lam. storage root yield and quality) planted in the following year. Treatments in these studies consisted of flumetralin at 0, 0.67, 1.01, 1.34, 2.02, and 2.69 kg active ingredient (a.i.)/ha applied for sucker control to tobacco 2 weeks after topping (WAT) using a ground sprayer equipped with 3 nozzles per row. In 2012, 3 additional treatments included flumetralin at 1.01 and 2.02 kg/ha applied 2 WAT with a dropline method, and a lay-by treatment of 532 g a.i./ha pendimethalin at 4 to 5 weeks after tobacco transplanting followed by (fb) 1.01 kg/ha flumetralin at 2 WAT (using a 3-nozzle boom sprayer). Sweet potato planted the following year (2011) after tobacco had reduction in no. 1 sweet potato storage root yield in the 2.69 and 2.02 kg/ha flumetralin treatments applied with a 3-nozzle boom sprayer in 2011 and with both application methods (3-nozzle boom sprayer, dropline) in 2013, respectively. Flumetralin application rate (both years) or application method (2013) did not affect jumbo and marketable sweet potato yields. The lay-by treatment of pendimethalin followed by flumetralin in tobacco did not reduce yield (across all grades) of sweet potato planted the following year after tobacco. Overall, these results showed that no concern should exist for sweet potato planted the following year if flumetralin is applied at ≤1.34 kg a.i./ha (label-recommended dose) in tobacco.
Pesticide residues found on cured tobacco (Nicotiana tabacum L.) remain a large concern to the allied tobacco industry. To quantify maximum expected cured leaf residues, 3 active ingredients (fluopicolide, indoxacarb, and oxathiapiprolin) were applied to flue-cured tobacco grown in 6 North Carolina environments from 2016 to 2018. Fluopicolide residues were consistently among the highest documented in this evaluation (7.25 mg/kg maximum), which was most likely a result of the compound having the shortest preharvest interval (PHI; 7 days) among the products tested. The highest indoxacarb residue was 2.15 mg/kg, which was identified in lower-stalk-position samples collected from 1 environment in 2018. Additional data suggest that indoxacarb residues are likely to be <2.0 mg/kg. Oxathiapiprolin was below the limit of quantification (0.09 mg/kg) in 98.6% of the samples analyzed and averaged 0.10 mg/kg in the lower-stalk position of 1 environment in 2017. It is plausible that residues from commercial farming operations would be lower than those reported because of integrated pest management (IPM) practices. Further investigations are warranted to better identify residues resulting from applications delivered using recommendations put forth by Cooperative Extension Services in the southern United States.
Experiments were initiated in 2015 to evaluate the efficacy of chemical topping for burley tobacco (Nicotiana tabacum L.). The major objectives for this study were to determine the optimum timing of suckercide application and appropriate cultivar maturity for effective chemical topping. Burley tobacco cultivars TN 90 (medium maturity), KT 210, and KT 215 (late maturity) were chemically topped at the 10% button, 50% button, and 10% bloom growth stages. The 10% button and 50% button application timings were best suited for chemical topping practices. Treatments that targeted the 10% bloom stage did not completely halt inflorescence growth; however, all application timings resulted in excellent sucker control. Both medium and late maturing burley cultivars proved to be acceptable for chemical topping methods; however, timing the suckercide application may be less difficult with later maturing cultivars. Chemically topped treatments generally resulted in shorter, narrower tip leaves than manually topped treatments. There were no significant differences in total yield of TN 90 when comparing tobacco that was manually topped at 10% bloom to tobacco that was chemically topped at 10% button, 50% button, or 10% bloom across all environments. In 4 out of 6 environments, total yield was not significantly different between manual topping and any chemically topped application timing in the late maturing burley cultivars; however, at least 1 chemically topped application timing had equivalent yield to manually topped tobacco in all environments.
Tobacco-specific nitrosamines (TSNAs) are known carcinogens in cured tobacco. They are produced primarily during the curing process, but agronomic practices occurring in the field as well as handling practices after curing may also influence TSNA levels, particularly if cured leaf is stored at high moisture. After curing and during market preparation, the cured leaf must be supple to avoid breakage. Ideally, this is after a period of wet weather during which the leaf absorbs moisture and comes into order or case. Often the weather remains dry for long periods after curing, and growers resort to artificial ordering to take down a sufficient amount of their crop to work on for several days, during which time the tobacco is bulked. The effect of this artificial ordering on TSNAs during short-term storage is not known. Field experiments were conducted in each of 3 years at two locations in Kentucky to evaluate TSNA accumulation following several ordering methods in dark air-cured and burley tobacco types. Treatments included natural ordering and variants of steaming and misting, which are both commonly used artificial ordering methods. At the Princeton location, samples were taken within 24 hr after the ordering treatments were done. In Lexington, samples were taken sequentially at takedown, after ordering, and after 14 d in the bulk. There were limited and inconsistent differences in total TSNAs between methods of ordering, and the TSNA levels were not affected by the moisture content of the leaf during bulking. There was a significant increase in TSNAs in the 24-hr period between takedown and bulking, which cannot be explained. We conclude that, in Kentucky, growers should use ordering methods that are best suited for their production system, but this may not be the case in warmer climates.
The act of topping tobacco (Nicotiana tabacum L.) involves the removal of the terminal bud or inflorescence of the tobacco plant. This practice ordinarily is accomplished by manually removing the top of each tobacco plant in an entire field, which is labor intensive and costly. The major objectives for this research were to determine which labeled suckercides could be used effectively for chemical topping of burley tobacco and the effect of suckercide rate on sucker control, yield, leaf quality, maleic hydrazide (MH) residues, and leaf chemistry. A study was initiated at Murray, Princeton, and Lexington, KY that investigated the efficacy of suckercide applications using combinations of MH, butralin, and fatty alcohols (FA). The terminal bud was not well controlled with FA or butralin alone, nor was adequate sucker control or total yield achieved. A significant reduction in total yield and sucker control were observed when plants were chemically topped with MH alone compared to manually topped or chemically topped with a tank mixture of MH and butralin at Princeton only. At the other locations, all chemically topped plants had similar yield to manually topped plants. Our data suggested that chemical topping of burley tobacco with a tank mixture of MH and a local systemic can be an acceptable alternative to manual topping as total yield and leaf quality grade index were not significantly different at any location. Total tobacco-specific nitrosamine (TSNA) content and MH residues were significantly lower with chemical topping treatments in some years and locations.
Organically derived fatty alcohol is useful for the control of tobacco axillary buds (suckers) and is greatly needed by commercial organic tobacco farmers. Recently, its approval by the U.S. Department of Agriculture (USDA)-National Organic Program has been scrutinized. The objective of this research was to evaluate the suggested alternatives: pelargonic acid, vegetable oil, canola oil, and peppermint + spearmint oil using two different application methods, a standard 3-nozzle boom or a dropline. Chemical injury was not observed within any treatment except for those containing pelargonic acid. Injury was greatest when applied with the 3-nozzle boom and was reduced by nearly 50% with the dropline; however, injury after the dropline application was 2.5 to 7 times greater than any other treatment. Despite significant injury, sucker control was acceptable with pelargonic acid (≈90%) and was similar to that resulting from fatty alcohol (99–100%). Sucker control was <40% among all other treatments, with peppermint + spearmint oil providing better efficacy than canola (10 to 15%) or vegetable oil (−1 to −10%). Cured leaf yield, quality, and value were likewise greatest in fatty alcohol treatments because of maximized sucker control and minimized chemical injury. Producers are encouraged to utilize fatty alcohol until the alternative products can be reformulated and re-evaluated.
Alkaloids are important compounds found in Nicotiana plants, essential in plant defense against herbivores. The main alkaloid of Nicotiana tabacum, nicotine, is produced in roots and translocated to the leaves. Nicotine is formed by a pyrrolidine and a pyridine ring in a process involving several enzymes. The pyridine ring of nicotine is derived from nicotinic acid, whereas the pyrrolidine ring originates from polyamine putrescine metabolism. After synthesis in root cortical cells, a set of transporters is known to transport nicotine upward to the aerial part and store it in leaf vacuoles. Moreover, nicotine can be metabolized in leaves, giving rise to nornicotine through the N-demethylation process. Some Nicotiana wild species produce acyltransferase enzymes, which allow the plant to make N-acyl-nornicotine, an alkaloid with more potent insecticidal properties than nicotine. However, although we can find a wealth of information about the alkaloid production in Nicotiana spp., our understanding about nicotine biosynthesis, transport, and metabolism is still incomplete. This review will summarize these pathways on the basis on recent literature, as well as highlighting questions that need further investigation.
With rising input costs, flue-cured tobacco producers must consider modern fertility programs that focus on reduced application rates of alternative nutrient sources. To demonstrate the usability of these fertility programs, research was conducted in 2012, 2013, and 2014 to assess the impacts of reduced input fertilizer programs on flue-cured tobacco produced in the North Carolina Piedmont. Treatments evaluated included all possible combinations of 2 rates of liquid nitrogen (72 and 95 kg N/ha) and 3 rates of phosphorus (0, 25, and 56 kg P2O5/ha). Treatments were arranged in a randomized complete block design with a factorial treatment arrangement and replicated 4 times within each environment. Results confirm that lower application rates of nitrogen and phosphorus are acceptable for tobacco growth and development in the North Carolina Piedmont, as there were no differences in early-season tobacco growth or final leaf yield, quality, and value among the treatments imposed. In addition, the application of liquid nitrogen is suitable for the production of tobacco with acceptable leaf yield and quality. Producers in this region should consider the nutrient sources and application rates evaluated in this study in order to remain economically and environmentally sustainable.
Significant variability in cured-leaf tobacco-specific nitrosamine (TSNA) content is commonly observed when sampling within dark air-curing barns. This variability may be due to inconsistency in the curing environment within different areas of the barn. A study was initiated in 2012, through support from a CORESTA Study Grant, to evaluate if cured-leaf TSNA content is related to microenvironmental conditions in the barn. Low-converter (TRsc) and high-converter (TRHC) selections of TR Madole dark tobacco were air cured in barns near Princeton and Lexington, KY. Temperature and relative humidity were measured with data loggers placed at 27 different locations within each barn for the duration of curing. There were no significant effects of individual data logger placement in either variety selection on hours above 24°C temperature, hours above 80% relative humidity, or TSNA; therefore, we investigated these data within the 3-dimensional aspects of tier, room, and bent within each barn. There were various effects of tier, room, and bent on temperature, relative humidity, and TSNA. Temperature data followed an understandable pattern across tiers in the barn within each year and location; however, relative humidity and TSNA were more difficult to characterize adequately. There was a significant relationship between hours above 24°C and TSNA, but not hours above 80% relative humidity. This study has shown that the effect of within-barn position on TSNA cannot be easily predicted.
From 2013 to 2015, research was conducted to estimate the maximum expected residue levels for the insecticides cyantraniliprole and spinosad following application to flue-cured tobacco. Data were generated in order to assist industry in establishing Guidance Residue Limits for both compounds. The insecticides were applied to fields of tobacco at maximum rates in accordance with the labeled rates and the harvested/cured leaf was analyzed in a lab for chemical residues. The findings indicated that the expected residues on cured leaf would be low or not quantifiable under existing detection techniques.
Field experiments were conducted in 2012, 2013, and 2014 near Murray, KY to evaluate response of dark fire-cured tobacco to potassium rate and application method. Treatments included 4 rates of potassium based on soil test K values with potassium sulfate (0–0–50) at 0%, 50%, 100%, and 150% of the recommended potassium rate in each year. All potassium treatments were either manually broadcast applied and incorporated 1 day prior to transplanting or manually band applied and incorporated 7 days after transplanting. Based on soil tests for the location of the 2012–13 tests, a higher rate of potassium fertilizer was recommended, compared to the 2014 location. Potassium rate and application method did not have a significant effect on yield components (lug, second, and leaf) in any year; however, there was a response in 2012–13 for total yield. Within the 100% recommended rate in 2012–13, broadcast (3,367 kg ha−1) application of potassium resulted in significantly higher yield than banded application (3,001 kg ...
One hundred eighty four strains of Ralstonia solanacearum isolated in 2007 and 2008 from 11 tobacco fields in North Carolina were evaluated for genotypic diversity and aggressiveness. All strains were race 1, biovar 1, and belonged to phylotype II. Genetic diversity of the strains was assessed with the use of repetitive sequence–based polymerase chain reaction. DNA primers (REP, ERIC, and BOX) were used to generate genomic fingerprints. Both REP and BOX revealed 3 patterns: Ar, Cr, and Dr and Ab, Cb, and Db, respectively. Five patterns were identified with ERIC-PCR. Pattern Ae was found in 80% of the strains collected. Pattern Be was in 4%, pattern Ce in 13%, pattern De in 2%, and pattern Ee in 1% of the strains collected. Cluster analyses showed that the strains were 88% similar and constitute a rather homogeneous group. Aggressiveness of strains was evaluated on 3 tobacco cultivars with different levels of resistance to bacterial wilt. Overall, aggressiveness depended on the field from which the strains...
