Flue-cured Tobacco Production Research Articles

First Report of Charcoal Rot on Tobacco Caused by Macrophomina phaseolina in Hunan Province, China.

Flue-cured tobacco (Nicotiana tabacum L.) is a significant cash crop globally. In August 2022, necrotic lesions on stem associated with root rot and wilting were observed on flue-cured tobacco (Cv. Yunyan 87) in fields located in Banxin village (27.95N,109.60E) of Fenghuang county in Xiangxi Autonomous Prefecture, Hunan Province, China. The affected and damaged area of tobacco is approximately 10 hectares, with adisease incidence of 60%. Lots of small black speckling within the lower stem of the affected plant, vascular tissue changed to black, dry rot, and looked like charcoal breezes. Small pieces were cut from healthy and diseased tissues, surface sterilized with 5% NaClO for 3 min and 75% ethanol for 1 min, rinsed with sterile distilled water and air-drying, incubated on oat medium incubated at 28℃ for five days. These isolates grew fast and produced typical black microsclerotia. The morphological were septate hyphae and microsclerotia. The microsclerotia were black and regularly round, with a 42.5 - 92.9 μm diameter. These morphological features were consistent with Macrophomina phaseolina (Smith and Wyllie 1999). The internal transcribed spacer (ITS) rDNA and translation elongation factor 1-α (TEF1-α) genes of three representative isolates were amplified and sequenced using the primers ITS1/ITS4 and EF1-728F/EF2R (Machado et al. 2019). Our resulting sequences (GenBank accessions OR435093, OR435101, OR435102 for ITS; OR891780, OR891781 and OR891782 for EF1-α) showed 99-100% similarity with M. phaseolina by NCBI blast. Phylogenetic analysis was conducted using MEGA-X software with the NJ method. The combined sequences grouped with isolates to M. phaseolina with 100% bootstrap support. The strain XF22 has been sent to the China General Microbiological Culture Collection Center (CGMCC3.25349). Pathogenicity tests were conducted by inoculating potted plants (six plants per isolate, three times) from 45 day-old tobacco seedlings cv. Yunyan 87. Stems were randomly gently scratched with sterile needles, and a 5 mm agar disc with mycelium of the pathogen was attached to the surface of each wound, with a sterilized agar disc as control. Inoculated seedlings were incubated in growth chambers at 26℃ and 60% RH with a 12 h photoperiod/day. After ten days, symptoms that brown or black lesions on the inoculated lesions were dotted with numerous black, hard microsclerotia similar to those naturally occurring on the diseased plants, but not on the control plants. The same pathogen was re-isolated consistently, fulfilling Koch's postulates. Based on morphological, molecular, and pathogenicity test results, these isolates were identified as M. phaseolina. Charcoal rot of tobacco, caused by M. phaseolina was previously found in Guangxi in 1989 (Zhu et al. 2002), while this is the first report of M. phaseolina causing charcoal rot on flue-cured tobacco in Hunan, China. We speculate that the planting area is influenced by the preceding crop sesame. The soil carries M. phaseolina, which can cause stem rot of sesame, leading to the occurrence of tobacco charcoal rot. Our results indicated that charcoal rot caused by M. phaseolina is a new threat to flue-cured tobacco production and lue-cured tobacco might be acting as a reservoir and spreading this pathogen to other economically crops in China.

Intercropping system modulated soil-microbe interactions that enhanced the growth and quality of flue-cured tobacco by improving rhizospheric soil nutrients, microbial structure, and enzymatic activities.

As the promotive/complementary mechanism of the microbe-soil-tobacco (Nicotiana tabacum L.) interaction remains unclear and the contribution of this triple interaction to tobacco growth is not predictable, the effects of intercropping on soil nutrients, enzymatic activity, microbial community composition, plant growth, and plant quality were studied, and the regulatory mechanism of intercropping on plant productivity and soil microenvironment (fertility and microorganisms) were evaluated. The results showed that the soil organic matter (OM), available nitrogen (AN), available phosphorus (AP), available potassium (AK), the urease activity (UE) and sucrase activity (SC), the diversity, abundance, and total and unique operational taxonomic units (OTUs) of bacteria and fungi as well as plant biomass in T1 (intercropping onion), T2 (intercropping endive), and T3 (intercropping lettuce) treatments were significantly higher than those of the controls (monocropping tobacco). Although the dominant bacteria and fungi at the phylum level were the same for each treatment, LEfSe analysis showed that significant differences in community structure composition and the distribution proportion of each dominant community were different. Proteobacteria, Acidobacteria, and Firmicutes of bacteria and Ascomycota and Basidiomycetes of fungi in T1, T2, and T3 treatments were higher than those of the controls. Redundancy analysis (RDA) suggested a close relation between soil characteristic parameters and microbial taxa. The correlation analysis between the soil characteristic parameters and the plant showed that the plant biomass was closely related to soil characteristic parameters. In conclusion, the flue-cured tobacco intercropping not only increased plant biomass and improved chemical quality but also significantly increased rhizospheric soil nutrient and enzymatic activities, optimizing the microbial community composition and diversity of rhizosphere soil. The current study highlighted the importance of microbe-soil-tobacco interactions in maintaining plant productivity and provided the potential fertilization practices in flue-cured tobacco production to maintain ecological sustainability.

Suitability of Blended Minjingu Fertilisers for Flue-Cured Tobacco Production in Tanzania’s Sandy Soils

Objective: To evaluate the suitability of minjingu N10P18K24 top-dressed with minjingu CAN27% N fertilizer blends for tobacco yield and quality. Methods: The experiment was laid out in a randomized complete block design in 3 sites during the 2020-2021 farming season at Mtanila (Chunya), Tumbi (Tabora) and Songambele (Urambo). The experiment was done 3 times and used 5 types of treatment as described below: T1=standard N10P18K24+standard CAN27%, T2=minjingu N10P18K24+minjingu CAN27%, T3=minjingu N10P18K24 standard CAN27%, T4=standard N10P18K24 minjingu CAN27% and T5=Absolute control. The plot measured was 6m×6m. Tobacco variety (Nicotiana tabacum L. cv. K326) seed sourced from the Tobacco Research Institute of Tanzania was used in the experiment. Seedbeds were first raised in a nursery with a spacing of 1.5×20m before being transplanted in field plots after 60 days. Basal application of N10P18K24 fertilizer was done a week after transplanting tobacco seedlings, followed by top-dressing CAN27N% fertilizer 2 weeks after application of N10P18K24 fertilizer. All agronomic management procedures were strictly observed. Results: Across the sites, the tobacco plants fertilized with minjingu basal N10P18K24 fertilizer and top-dressed with minjingu CAN27% (T2) yielded 1942.59kg ha-1 of dry tobacco leaf, which did not significantly (P≤0.001) differ with the yield of 2033.64kg ha-1 from plots fertilized with the standard N10P18K24 and top-dressed with the standard CAN27% (T1). The tobacco plants fertilized with standard N10P18K24 and top dressed with minjingu CAN27% produce higher yields of dry leaf (1738.88kg ha-1). This indicates that minjingu CAN27% fertilizer significantly contributed to the increased yield when applied in combination with minjingu N10P18K24. Conclusion: Minjingu N10P18K24 and minjingu CAN27% yielded tobacco plants that were not significantly different to those yielded by application of standard N10P18K24 and standard CAN27%. Additionally, the minjingu CAN27% contributed significantly to the dry leaf yield and quality of the tobacco.

Screening and Testing of Anti-Slagging Agents for Tobacco-Stalk-Based Biomass Pellet Fuel for Tobacco Curing

Using tobacco stalks as a biomass fuel for flue-cured tobacco production creates a closed, green production cycle. Tobacco stalks are rich in cellulose and can be crushed to produce biomass pellet fuel (BPF). However, single flue-cured tobacco stalk (FCTs) BPF can easily slag during flue-cured tobacco heating (FTH), which affects the operation of biomass burners. In this study, five anti-slagging agents (ASAs), one organic (sodium carboxymethyl cellulose, CMC) and four inorganic (kaolin, KLN; diatomite earth, DTE; calcium carbonate, CCO; and calcium dihydrogen phosphate, CHO)], were compared. An ash fusibility test was conducted in two steps to optimize the proportion and treatments that were then screened using FTH. Compared with pure FCT-based BPFs, the slag resistance of 2% CCO and CHO could be controlled below 15%. The emission of particulate matter from chimneys burning BPF with 2% CCO was lower than that with other ASAs. The ASAs achieved complete combustion with low carbon monoxide content in the tail gas. Considering the anti-slagging effect and economic cost, 2% CCO was the best additive for the biomass burner. These results provide a reference for FCT-based BPF production.

Comparative Analysis of the Rhizospheric Bacterial Communities of Flue-Cured Tobacco Affected by Granville Wilt

Ralstonia solanacearum is a yield-limiting disease in flue-cured tobacco production in the Southeast United States and other major producing countries worldwide. Studies determining the association between the rhizospheric bacterial community composition, R. solanacearum distribution in the field, and soil physicochemical properties have not been conducted. In this study, the 16S rRNA gene of 144 rhizosphere samples, collected from three different fields (A, B, and C) in North Carolina, were sequenced using Illumina MiSeq v3 chemistry to (i) compare the rhizospheric bacterial community of healthy and diseased plants inside and outside “hot-spots”; (ii) identify potential bacterial indicators for Granville wilt suppression; and (iii) examine edaphic factors associated with rhizospheric bacterial composition and disease distribution in flue-cured tobacco fields. The phylum Proteobacteria was the most abundant in all fields and sampled locations within fields. Eighteen genera, including Bacillus and Pantoea, which are known antagonists of R. solanacearum, were consistently found in the rhizosphere samples from healthy plants in only one of the fields. Organic matter, Mn, and Ca contents were descriptive of the rhizosphere community structure found in healthy samples. In conclusion, the results obtained from the present study suggest that disease outcome and distribution could be associated with variation on community composition driven by edaphic factors and the presence of an antagonist. This study provides evidence of naturally occurring antagonists that could be exploited in novel management strategies for R. solanacearum suppression in modern flue-cured production systems. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Diff erent Levels of Nitrogen Fertilizer in Nursery Stage Positively Aff ect the Activity of Defense-related Enzymes and Resistance of Tobacco Plant to Phytophthora nicotianae

Black shank caused by Phytophthora nicotianae is a serious threat to the production of better-quality fl ue-cured tobacco. Protein’s are executors of plant functions and most disease resistance mechanisms in plants are related to differential expression of proteins. In our previous study, 17 different proteins induced by P. nicotianae were screened out through proteomics analysis. In this study, we evaluated the effect of three different levels of nitrogen fertilizer (High, medium, and low) at the seedling stage on the expression of these proteins, physiological response of fl ue-cured tobacco, and occurrence of black shank disease. Results of this study showed that before and after inoculation of P. nicotianae, the activity of defense-related enzymes except for MDA contents in tobacco plants grown under low- nitrogen level was higher than tobacco plants grown under the high-nitrogen level at seedling stage. Through analysis of 17 different proteins, we found the expression of 12 proteins (three proteins involved in photosynthesis, six proteins involved in oxidative phosphorylation, one protein involved in tricarboxylic acid cycle, one heat shock protein, and one 14-3-3 protein) were up-regulated in tobacco seedlings raised under low nitrogen level. However, the expression of fi ve pathogenesis-related proteins was not detected. This study highlights the effect of effi cient use of nitrogen fertilizer during the nursery growing stage for producing healthy tobacco seedlings. It is concluded that a proper supply of nitrogen fertilizer at the seedling stage ensures the quality production of tobacco seedlings and reduces the incidence of black shank disease.

Unraveling the expression of differentially expressed proteins and enzymatic activity in response to Phytophthora nicotianae across different flue-cured tobacco cultivars

BackgroundBlack shank disease caused by Phytophthora nicotianae is a serious threat to flue-cured tobacco production. Whole-plant resistance is characterized by the expression of a number of pathogenesis-related proteins, genes, and the activity of different defense-related enzymes. In this study, we investigated the activity of defense-related enzymes and expression of differentially expressed proteins through the iTRAQ technique across two flue-cured tobacco cultivars, i.e., K326 and Hongda, in response to the black shank pathogen.ResultsResults showed that the highest disease incidence was recorded in flue-cured tobacco cultivar Hongda compared with K326, which shows that Hongda is more susceptible to P. nicotianae than K326. A total of 4274 differentially expressed proteins were detected at 0 h and after 24 h, 72 h of post-inoculation with P. nicotianae. We found that 17 proteins induced after inoculation with P. nicotianae, including pathogenesis (5), photosynthesis (3), oxidative phosphorylation (6), tricarboxylic acid cycle (1), heat shock (1), and 14–3-3 (1) and were involved in the resistance of flue-cured tobacco against black shank disease. The expression of 5 pathogenesis-related proteins and the activities of defense-related enzymes (PPO, POD, SOD, and MDA) were significantly higher in the leaves of K326 than Hongda after inoculation with P. nicotianae.ConclusionThese results provide new molecular insights into flue-cured tobacco responses to P. nicotianae. It is concluded that differences in protein expressions and defense-related enzymes play an important role in developing resistance in flue-cured tobacco cultivars against black shank disease.

Microbial Cross-Talk: Dissecting the Core Microbiota Associated With Flue-Cured Tobacco (Nicotiana tabacum) Plants Under Healthy and Diseased State.

Bacterial wilt caused by Ralstonia solanacearum is a devastating disease of flue-cured tobacco production which poses significant yield losses all around the world. In this study, we evaluated the rhizosphere microbiome of healthy and bacterial wilt-infected (diseased) flue-cured tobacco plants through amplification of V3-V4 and ITS1-5f variable regions of 16S and internal transcribed spacer (ITS) rRNA. The study was based on the location (Qujing, Shilin, and Wenshan), plant components (rhizosphere soil and roots), and sample types (healthy and diseased) to assess the diversity of bacterial and fungal communities. Bacterial and fungal communities present in roots primarily emanated from rhizosphere soil. Healthy flue-cured tobacco plants exhibit high microbial diversity compared to diseased plants. Among three variables, plant components significantly influence the diversity of microbial communities, whereas rhizosphere soil harbors higher microbial diversity than roots. Bacterial phyla Cyanobacteria and Proteobacteria were found in high relative abundance in roots and rhizosphere soil samples, respectively. As far as fungi is concerned, a high relative abundance of Ascomycota and Basidiomycota was found in both rhizosphere soil and root. Bacterial genera such as Bacillus, Bradyrhizobium, Ensifer, Neorhizobium, and Lysobacter related to plant growth promotion and disease suppressing abilities were dominant than fungal genera. Analysis of relative abundance at specie-level revealed that most fungal species are pathogenic to flue-cured tobacco and could provide a conducive environment for wilt infection. In conclusion, R. solanacearum significantly influences the microbial diversity of flue-cured tobacco plants and negatively affects the bacterial community composition. Altogether, our study demonstrates the complexity of bacterial and fungal communities that possibly interact with each other (microbe–microbe) and host (host–microbe). This cross-talk could be helpful for healthy flue-cured tobacco plant growth and to induce resistance against bacterial wilt disease.

Bacillus amyloliquefaciens WS-10 as a potential plant growth-promoter and biocontrol agent for bacterial wilt disease of flue-cured tobacco

BackgroundBacterial wilt disease caused by the soilborne bacterium Ralstonia solanacearum is a serious threat to flue-cured tobacco production. In this study, an indigenous disease suppressive Bacillus strain was isolated from the rhizosphere soil of healthy tobacco plants, and its biocontrol and plant growth promoting (PGP) potential were evaluated in in-vivo and in-vitro assays.ResultsThrough isolation and screening of 250 isolates, WS-10 was found to be the best candidate antagonistic strain against R. solanacearum (WS-001). In-vitro assays revealed that the isolated strain WS-10 (Bacillus amyloliquefaciens) showed an effective antagonistic activity against R. solanacearum WS-001 and several plant-pathogenic fungi. As promising PGP rhizobacteria, WS-10 had the ability of nitrogen fixation, solubilization of inorganic potassium and phosphate, and biosynthesis of indole-3-acetic. In a co-culture assay, it significantly inhibits the growth of WS-001. Our greenhouse experiments showed that the soil physicochemical properties and accumulation of dry matter contents in different plant parts (roots, stems, and leaves) were significantly increased in the presence of B. amyloliquefaciens WS-10. The soil treated with B. amyloliquefaciens WS-10 displayed significantly higher values of the average well color development index, the utilization ability of 6 types of carbon sources by rhizosphere microorganisms, and the diversity indices of the rhizosphere microbial communities. In planta assay, B. amyloliquefaciens WS-10 significantly reduced tobacco bacterial wilt disease incidence by up to 73.36, 43.82, and 86.82% under three different treatments by improving the functional diversity and biological activity of the soil microbial community.ConclusionsObtained findings suggested that B. amyloliquefaciens WS-10 had an excellent potential as a growth-promoting and biocontrol agent of tobacco bacterial wilt disease due to its multiple beneficial traits of nutrient solubilization and disease suppression. Thus, we conclude that B. amyloliquefaciens WS-10 was a high potential PGP and biocontrol strain for healthy production of tobacco crop.

Flue-cured tobacco (Nicotiana tabacum L.) leaf quality can be improved by grafting with potassium-efficient rootstock

The low Potassium (K) content in flue-cured tobacco leaves severely restricts the development of China's high-quality cigarette industry. To determine whether the quality of flue-cured tobacco leaves can be improved by grafting, a cross-grafting experiment of two different K-efficiency tobacco strain (Yunyan 87, main cultivar. WuFeng No.2, K-efficient genotype) was carried out. Measurement data from a field experiment with three K supply levels (0,135 and 270 kg K2O ha−1) and four grafting combinations [‘Wufeng No. 2’(W), ‘Yunyan 87’(Y), Y/W (Y grafted onto W) and W/Y (W grafted onto Y)] from 2018 to 2019 were used to evaluate the effect of grafting on flue-cured tobacco quality. The results demonstrated that the average leaf maturity in the grafted tobacco ‘Yunyan 87’ increased by 7.69 %. Meanwhile, maximum accumulation, rapid accumulation duration, and maximum relative accumulation rates of K and biomass in the grafting treatments were all improved over the growth period, and the K levels in the grafted tobacco leaves increased by 95.4 % on average. In addition, when potassium supply level was insufficient, the proportion of K+ in grafted tobacco leaves was higher than that in other treatments. In terms of commercial quality, the chemical and smoking quality of grafted tobacco leaves were 32.2 % and 7.1 % higher than those of ungrafted tobacco leaves. The grafted ‘Yunyan 87’ inherited the advantages of the scion in terms of flavor. At the same time, the combustibility of Y/W was improved by the characteristics of the rootstock, and its total score of quality was highest. The correlation analysis revealed that K accumulation was significantly related to the improvement of tobacco leaf quality. Therefore, increasing the K content and improving the quality of tobacco leaves through grafting is a feasible approach for the production of high quality flue-cured tobacco.

Biochar suppresses bacterial wilt disease of flue-cured tobacco by improving soil health and functional diversity of rhizosphere microorganisms

Bacterial wilt caused by Ralstonia solanacearum is a devastating disease of flue-cured tobacco production. Amendments of biochar in soil suppress the incidence of bacterial wilt disease by improving soil health and functional diversity of rhizosphere microbes. In this study, we observed the effect of 0–5% application rate of tobacco stem biochar on soil health and the occurrence of tobacco bacterial wilt disease. Results demonstrated that the application of 2% tobacco stem biochar significantly improves soil physicochemical properties, microbial biomass carbon and nitrogen, and the functional diversity of microbes in the rhizosphere. The ability of rhizosphere microorganisms to utilize six types of carbon sources was significantly improved under the 2% application rate of tobacco stem biochar, which reduced the incidence of bacterial wilt disease and R. solanacearum population in the rhizosphere of tobacco plants. Biochar also increases the accumulation of dry matter contents in the roots, stems, and leaves of tobacco plant. We conclude that tobacco stem biochar at a certain level improves the soil physicochemical properties, functional diversity of rhizosphere microorganisms, mitigates the pathogen population, and reduces disease incidence. This study highlights the potential use of tobacco stem biochar to manage the bacterial wilt disease.

Push/Pull Factors, Networks and Rural Labor Migration: Based on the Survey Data of Rural Labor Force in Tobacco Enterprises

Objectives: The “push-pull theory” analyzes the dynamic mechanism of the cross-border flow of labor force, and explains that the flow of labor force between countries is generated by the combined action of “push” and “pull”. Tobacco has always been an important cash crop in China, providing a lot of financial support for the rapid development of China’s economy. Tobacco production is the premise of the development of tobacco industry. The shortage of tobacco planting labor force and the decline of quality restrict the tobacco production and the development of the tobacco industry. Based on the “push-pull theory”, the researcher focuses on the survey data of the rural labor force of a specific Labor Cooperation Company. This paper clarified the current situation and transfer characteristics of rural labor force in tobacco areas, discussed the impact of labor force transfer on flue-cured tobacco production, and put forward the strategies to solve the dilemma of rural labor force transfer in tobacco areas.Therefore, the suggestion of taking the city as the center and form a network of migrant workers to enhance the sense of belonging of them is proposed.

Study on the relationship between bacterial wilt and rhizospheric microbial diversity of flue-cured tobacco cultivars

Bacterial wilt caused by Ralstonia solanacearum, is one of the serious soil-borne diseases in flue-cured tobacco production areas in China. However, it was found that the occurrence of bacterial wilt not only varied with different cultivars but also varied with various sites even under the condition of planting the same variety. It suggests that the occurrence of bacterial wilt could be controlled by regulating soil microorganism and the growth environment. Therefore, the relationship between microorganism’s diversity in the rhizosphere and actual incidences were evaluated on the number of symptomatic plants and the functional diversity of soil microorganisms in field trials on two sites. The results showed that the incidence of bacterial wilt in the same cultivar was varied between the two experimental sites. However, the same trend was found in the number of rhizospheric microbes among the three varieties except for fungi. Also, a good relationship was found between the number of pathogens, microbial functional diversity in the rhizosphere, and actual incidences. The utilization intensity of carbohydrates, amino acids, carboxylic acids, polymers, amines, and carbon utilization of rhizospheric soil microbial community was negatively related with the occurrence of bacterial wilt while it was on the opposite for the utilization intensity of phenolic acids. The results revealed that the mechanism for resistance in flue-cured tobacco was directly associated with the number of pathogenic microorganisms in rhizosphere and the diversity of rhizospheric microbes. By improving the diversity of rhizospheric microbes, the incidence of tobacco bacterial wilt disease can be reduced.

Reproduction of Meloidogyne arenaria race 2 on flue-cured tobacco with putative resistance derived from Nicotiana repanda.

Chemical controls for root-knot nematodes are increasingly restricted due to environmental and human health concerns. Host resistance to these nematodes is key to flue-cured tobacco production in Virginia. Resistance to Meloidogyne incognita races 1 and 3, and race 1 of M. arenaria is imparted by the gene Rk1, which is widely available in commercial flue-cured tobacco. Rk2 imparts increased resistance to M. javanica when stacked with Rk1 and is becoming commercially available. The efficacy of Rk2 against M. arenaria race 2, which is increasingly prevalent in Virginia, is unclear. Greenhouse trials were conducted in 2017 to determine how potential resistance derived from N. repanda compares to the root-knot nematode resistance afforded by Rk1 and Rk2. Trials were arranged in a completely randomized block design and included an entry with traits derived from N. repanda, a susceptible entry and entries possessing Rk1 and/or Rk2. Data collected after 60 days included percent root galling, egg mass counts, and egg counts. Root galling and reproduction were significantly lower on the entry possessing traits derived from N. repanda relative to other entries, suggesting that the N. repanda species may hold a novel source of root-knot nematode resistance for commercial flue-cured tobacco cultivars.

Plant-Microbiome Interactions for Bacterial Wilt Suppression in Modern Tobacco Production

The soil-borne bacterium Ralstonia solanacearum continues to represent a major threat to flue-cured tobacco (Nicotiana tabacum) production in the southeastern United States and other major producing regions throughout the world. Beneficial microorganisms naturally found in the soil represent an alternative solution for R. solanacearum’s suppression that may reduce soil health impacts of current management strategies. Biological controls and microbiota manipulation together represent a unique opportunity to reduce disease caused by R. solanacearum. Current high-throughput DNA sequencing technologies and advances in bioinformatic analyses enable culture-independent approaches to study root-associated microorganisms and their interactions. The structure and dynamics of tobacco root-associated microbiota, as well as functional capacities of certain taxa, may improve how we apply disease management strategies in the field. Through this review we summarize our current understanding on (i) the role of bacterial microbiota on R. solanacearum survival, (ii) the impacts of current management strategies on the soil bacterial communities, (iii) the rhizospheric and core microbiome composition and inheritance, (iv) the manipulation of the microbiota for enhanced disease suppression, and (v) the shortcomings of the application of plant-associated bacteria for disease suppression.

Application Progress of Microbial Fertilizers in Flue-Cured Tobacco Production in China

The followings were overviewed: the application of microbial fertilizers in China’s tobacco production; the influences of microbial fertilizers on the nutrients, microbial biomass and enzymatic activity in tobacco-planting soil; the influences of microbial fertilizers on flue-cured tobacco root system, tobacco yield as well as chemical properties and disease resistance of cured tobacco leaves; the influence of microbial fertilizers on continuous cropping obstacles of flue-cured tobacco, and their fertilizer saving effect. The problems in the existing researches were analyzed, and the future development direction of microbial fertilizers in tobacco production was discussed.

The response of flue-cured tobacco cultivar K326 to nitrogen fertilizer rate in China

AbstractNitrogen is an important element for the growth of flue-cured tobacco and is closely related to its yield and quality. In order to pursue higher economic benefits, excessive fertilizer is generally applied in flue-cured tobacco production, which is unfavourable for the sustainable development of flue-cured tobacco production and for the environment. In 2016 and 2017, experiments using different nitrogen fertilizer application rates in flue-cure tobacco were conducted in Yunnan province, and the changes in agronomic, economic and chemical indices as well as in residual soil nitrogen were compared. Linear and quadratic models were used to compare the response of tobacco to nitrogen fertilizer. With increasing nitrogen fertilizer rate, the proportions of superior to medium tobacco and the average price of flue-cured tobacco leaves initially increased and then decreased, while fresh weight, dry weight and the proportion of inferior tobacco showed the opposite trend. Total sugar and reducing sugar contents decreased with increasing nitrogen fertilizer rates, while total nitrogen and nicotine contents increased. Sensory evaluation scores had the highest value when 90 kg N/ha and 120 kg N/ha were applied. Soil nitrate contents increased as nitrogen fertilizer rate increased. The quadratic model was suitable for the response of cultivar K326 to nitrogen and 90 kg N/ha could meet the needs of cultivar K326.

Breeding for Yield, Quality and Associated Traits in the Zimbabwean Flue-Cured Tobacco (Nicotiana tabacum L.): A Review

Tobacco (Nicotiana tabacum L.) has grown to become a major cash crop and foreign currency earner in Zimbabwe. The crop’s popularity in the country is dependent on the climatic and soil conditions that promote the production of flavour style cures which are well sought after by the majority of tobacco merchants and cigarette manufacturers across the world. The success story of tobacco farming in Zimbabwe is mainly attributed to the presence of an organised research system in the form of the Tobacco Research Board (TRB) that includes a dedicated division in the research unit specialising in variety development and promotion. Improvement in yield and quality of the cured leaf has are the main objectives of flue –cured tobacco breeders. Since the beginning of research in flue cured tobacco production in Zimbabwe, a lot of effort has been dedicated to improving these and other associated traits. This review paper traces the process of breeding for improvement in yield and quality in flue-cured tobacco in Zimbabwe. It shows the methods employed and identifies some of the potential sources of genes for use in improvement in flue-cured tobacco yield and quality in present and future breeding work.

Study on Production Efficiency of Flue-cured Tobacco in China Based on DEA-Malmquist Model

Based on the input-output data of flue-cured tobacco production in 18 provinces of China from 2005 to 2016, the flue-cured tobacco production efficiency was calculated and analyzed. The results show that: Firstly, the total factor productivity (TFP) of flue-cured tobacco in China shows a growth trend, the main reason of the growth is the growth of the scale efficiency. The pure technical efficiency and the technical progress play a negative role to the promotion of total factor productivity. Secondly, in the provinces where total factor productivity declines, the leading factors of total factor productivity declines are different. For the provinces where total factor productivity increases, the leading factor of total factor productivity growth is the improvement of technical efficiency. Thirdly, the change of annual total factor productivity growth rate is unstable because of the uncoordinated change of technological progress and technological efficiency. We can improve the flue-cured tobacco productivity by large-scale production, improving management level, introducing advanced production technology and strengthening technological innovation.

Nitrogen Fertilizer Programs for Organic Flue-Cured Tobacco (Nicotiana Tabacum L.) Seedling 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.