Development of a stable attenuated double-mutant of tobacco mosaic virus for cross-protection

Tobacco(Nicotiana tabacum)and tomato(Solanum lycopersicum)are two major economic crops in China.Tobacco mosaic virus(TMV;genus Tobamovirus)is the most prevalent virus infecting both crops.Currently,some widely cultivated tobacco and tomato cultivars are susceptible to TMV and there is no effective strategy to control this virus.Cross-protection can be a safe and environmentally friendly strategy to prevent viral diseases.However,stable attenuated TMV mutants are scarce.In this study,we found that the substitutions in the replicase p126,arginine at position 196(R^(196))with aspartic acid(D),glutamic acid at position 614(E^(614))with glycine(G),serine at position 643(S^(643))with phenylalanine(F),or D at position 730(D^(730))with S,significantly reduced the virulence and replication of TMV.However,only the mutation of S^(643) to F reduced the RNA silencing suppression activity of TMV p126.A double-mutant TMV-E614G-S643F induced no visible symptom and was genetically stable through six successive passages in tobacco plants.Furthermore,our results showed that TMV-E614G-S643F double-mutant could provide effective protection against the wild-type TMV infection in tobacco and tomato plants.This study reports a promising mild mutant for cross-protection to control TMV in tobacco and tomato plants.

Plant Chemical Defenses against Insect Herbivores—Using theWild Tobacco as a Model

The Nicotiana genus, commonly known as tobacco, holds significant importance as a crucial economic crop. Confrontedwith an abundance of herbivorous insects that pose a substantial threat to yield, tobacco has developed adiverse and sophisticated array of mechanisms, establishing itself as a model of plant ecological defense. Thisreview provides a concise overview of the current understanding of tobacco’s defense strategies against herbivores.Direct defenses, exemplified by its well-known tactic of secreting the alkaloid nicotine, serve as a potent toxinagainst a broad spectrum of herbivorous pests. Moreover, in response to herbivore attacks, tobacco enhancesthe discharge of volatile compounds, harnessing an indirect strategy that attracts the predators of the herbivores.The delicate balance between defense and growth leads to the initiation of most defense strategies only after aherbivore attack. Among plant hormones, notably jasmonic acid (JA), play central roles in coordinating thesedefense processes. JA signaling interacts with other plant hormone signaling pathways to facilitate the extensivetranscriptional and metabolic adjustments in plants following herbivore assault. By shedding light on these ecologicaldefense strategies, this review emphasizes not only tobacco’s remarkable adaptability in its natural habitatbut also offers insights beneficial for enhancing the resilience of current crops.

Advances in Research on Synthetic Microbial Communities

The synthetic microbial community is a synthetic microbial system co-cultured with multiple species, which has the characteristics of clear composition and strong controllability. Compared with a single colony, it can achieve more complex functions and adapt to the changing environment more easily, so as to meet a wide range of needs. In this paper, the contents and concepts of microbial community and synthetic microbial community are briefly introduced, the principles that should be followed in the construction of microbial community are expounded, the methods and mathematical models used in the construction of synthetic microbial community are introduced, and the applications of synthetic microbial community in various fields are summarized. Finally, the challenges in the research of synthetic microbial communities are briefly described.

Rosaceae phylogenomic studies provide insights into the evolution of new genes

Rosa banksiae,known as Lady Banks'rose,is a perennial ornamental crop and a versatile herb in traditional Chinese medicine.Given the lack of genomic resources,we assembled a Hi Fi and Nanopore sequencing-derived 458.58 Mb gap-free telomere-to-telomere high-quality R.banksiae genome with a scaffold N50=63.90 Mb.The genome of R.banksiae exhibited no lineage-specific whole-genome duplication compared with other Rosaceae.The phylogenomic analysis of 13 Rosaceae and Arabidopsis through a comparative genomics study showed that numerous gene families were lineage-specific both before and after the diversification of Rosaceae.Some of these genes are candidates for new genes that have evolved from parental genes through fusion events.Fusion genes are divided into three types:Type-I and Type-II genes contain two parental genes that are generated by duplication,distributed in the same and different regions of the genome,respectively;and Type-III can only be detected in one parental gene.Here,Type-I genes are found to have more relaxed selection pressure and lower Ks values than Type-II,indicating that these newly evolved Type-I genes may play important roles in driving phenotypic evolution.Functional analysis exhibited that newly formed fusion genes can regulate the phenotype traits of plant growth and development,suggesting the functional significance of these genes.This study identifies new fusion genes that could be responsible for phenotype evolution and provides information on the evolutionary history of recently diverged species in the Rosa genus.Our data represents the major progress in understanding the new fusion genes evolution pattern of Rosaceae and provides an invaluable resource for phylogenomic studies in plants.

Lysobacter enzymogenes:A fully armed biocontrol warrior

Lysobacter enzymogenes is less-studied, but emerging as a powerful biocontrol bacterium producing multiple antimicrobial weapons including lytic enzymes, toxins, secondary metabolites and protein secretion systems.The loss of surface-attached flagellum, production of heat-stable antifungal factor(HSAF, also named as Ningrongmycin) as a novel antifungal antibiotic, and the use of the type Ⅳ secretion system(T4SS) rather than the common type Ⅵ secretion system(T6SS) to kill competitor bacteria make this species unique. These distinct features set L. enzymogenes apart from well-studied plant beneficial biocontrol agents, such as Bacillus and Pseudomonas. This review describes what takes L. enzymogenes to be a unique biocontrol warrior by focusing to illustrate how the lack of flagellum governs morphological and functional co-adaptability, what adapted signaling transduction pathways are adopted to coordinate the biosynthesis of HSAF, and how to ecologically adapt plant rhizosphere by cell-to-cell interacting with microbiome members via the bacterial-killing T4SS.

Identification of stably expressed QTL for resistance to black shank disease in tobacco(Nicotiana tabacum L.) line Beinhart 1000-1

Cigar line Beinhart 1000-1 has effective durable resistance to black shank(BS) and is considered one of the most resistant sources in tobacco(Nicotiana tabacum L.). To investigate the inheritance and identification of stable quantitative trait loci(QTL) for BS response, F2,BC1 F2 individuals and BC1 F2:3 lines were produced from a cross between Beinhart 1000-1 and Xiaohuangjin 1025. Two major quantitative trait loci(M-QTL) named qBS7 and qBS17 were repeatedly detected under different conditions. QTL qBS7 was mapped to the region between PT30174 and PT60621 and explained 17.40%–25.60% of the phenotypic variance under different conditions. The other QTL qBS17 in interval PT61564–PT61538 of linkage group 17 was detected in a BC1 F2 population in the field and in BC1 F2:3 in both the field and at the seedling stage, explaining 6.90% to 11.60% of the phenotypic variance. The results improve our understanding of the inheritance of resistance to BS and provide information that can be used in marker-assisted breeding.

High-density SNP genetic linkage map construction and quantitative trait locus mapping for resistance to cucumber mosaic virus in tobacco(Nicotiana tabacum L.)

Genetic linkage maps are essential for studies of genetics, genomic structure, and genomic evolution, and for mapping quantitative trait loci (QTL). Identification of molecular markers and construction of genetic linkage maps in tobacco (Nicotiana tabacum L.), a classical model plant and important economic crop, have remained limited. In the present study we identified a large number of single nucleotide polymorphism (SNP) markers and constructed a high-density SNP genetic map for tobacco using restriction site-associated DNA sequencing. In 1216.30 Gb of clean sequence obtained using the Illumina HiSeq 2000 sequencing platform, 99,647,735 SNPs were identified that differed between 203 sequenced plant genomes and the tobacco reference genome. Finally, 13,273 SNP markers were mapped on 24 high-density tobacco genetic linkage groups. The entire linkage map spanned 3421.80 cM, with a mean distance of 0.26 cM between adjacent markers. Compared with genetic linkage maps published previously, this version represents a considerable improvement in the number and density of markers. Seven QTL for resistance to cucumber mosaic virus (CMV) in tobacco were mapped to groups 5 and 8. This high-density genetic map is a promising tool for elucidation of the genetic bases of QTL and for molecular breeding in tobacco.

Changes of Polyphenols in Tobacco Leaves During the Flue-Curing Process and Correlation Analysis on Some Chemical Components

The changes of polyphenols in tobacco leaves during the flue-curing process and correlation analysis on some chemical components were studied. Leaf samples were taken from different tobacco-producing regions in Henan Province, China. The results indicated that the content of total phenols increased during the first 24 h of curing, and then decreased. It reached the lowest value at 72 h of curing and increased rapidly after that. The content of chlorogenic acid also increased during 0-24 h of curing. But the lowest point occurred at 60 or 72 h of curing and then it increased till the end of the curing process. The content of mtin generally increased with curing, and showed little fluctuations. The changes of PPO and POD activity were the opposite. Rutin was found to have a highly significant positive correlation with total sugar （r=0.822^＊＊）, but a highly significant negative correlation with starch, nicotine, and protein.

Differential responses of root growth to nutrition with different ammonium/nitrate ratios involve auxin distribution in two tobacco cultivars

Nitrogen(N), the major forms of which are nitrate(NO3–) and ammonium(NH4+), plays an important role in plant growth and mediation of root development. However, the role of auxin in root growth in response to different NH4+/NO3– ratios remains unclear. Two tobacco cultivars(Nicotiana tabacum L.) were adopted in this study, which displayed variant growth features under the situations with sole NO3– nutrition ratio(NH4+/NO3– ratio: 0/100), low NO3– nutrition ratio(NH4+/NO3– ratio: 97/3), and optimal NH4+/NO3– ratio(50/50). We investigated the effects of the different NH4+/NO3– ratios on the formation and elongation of lateral roots(LRs), auxin concentration, DR5::GUS expression, 3 H-labeled indole acetic acid([3 H]IAA) transport, and the expression of six PIN genes in tobacco roots. We also examined the effects of exogenous auxin and a transport inhibitor on LRs growth. The results are shown as follows, compared to optimal N nutrition conditions, the biomass and nitrogen(N) accumulation were largely reduced by sole and low NO3– nutrition treatment in NC89, but no difference was observed in Zhongyan 100. In most cases, sole and low NO3– nutrition impaired the elongation and formation of firstorder lateral roots(1° LRs), only in NC89, thus reducing the root growth. IAA concentration and DR5::GUS expression levels decreased in roots when NC89 was subjected to sole and low NO3– nutrition media, suggesting that different NH4+/NO3– ratios affect the transport of auxin from leaves to roots. Results were similar following exogenous NAA application to low NO3– nutrition treated seedlings. Based on direct [3 H]IAA transport measurement, the transport of polar auxin from shoots to roots decreased due to low NO3– nutrition. PIN4 expression levels were markedly decreased in roots of NC89by sole and low NO3– nutrition, while they were unaffected in Zhongyan 100 roots. Overall, our findings suggest that LRs formation in tobacco seedlings is regulated by NH4+/NO3– ratios via modifying polar transport of auxin.

Comparative transcriptome analysis reveals differential gene expression in resistant and susceptible tobacco cultivars in response to infection by cucumber mosaic virus

Cucumber mosaic virus(CMV) is one of the most severe viral diseases transmitted by aphids infecting Solanum crops in China, causing great losses of crop yields and income in rural communities.The tobacco cultivars NC82 and Taiyan 8 are closely related but differ in resistance to CMV.NC82 is susceptible to infection and Taiyan 8 is resistant, but the mechanisms underlying this difference in resistance are not clear.In this study, we conducted RNA sequencing to analyze changes in gene expression induced in the leaves of Taiyan 8 and NC82 upon systemic infection with CMV, compared with gene expression in the leaves of mock-inoculated plants.Leaves were sampled at one, three, eight, and 15 days after infection.In total, 3443 and 747 differentially expressed genes were identified in Taiyan 8 and NC82, respectively.Gene ontology and pathway enrichment analyses revealed that the different responses to CMV infection between cultivars were based on microtubulebased processes, pentose and glucuronate interconversions, plant–pathogen interaction,and hormone signal transduction pathways.Genes encoding pathogenesis-related proteins, disease-resistance proteins, lipoxygenase, cellulose synthase, an auxin response factor, and an ethylene receptor showed different expression patterns.The differences in gene expression following CMV infection likely contributed to the different resistance levels of these two tobacco cultivars.The comprehensive transcriptome dataset described here,which includes candidate response genes, will serve as a resource for further studies of the molecular mechanisms associated with tobacco defense responses against CMV.

Characterization and Expression Analysis of Four Glycine-Rich RNA-Binding Proteins Involved in Osmotic Response in Tobacco (Nicotiana tabacum cv. Xanthi)

Plants have developed many signals and specific genes＇ regulations at both transcriptional and post-transcriptional levels in order to tolerate and adapt to various environmental stresses. RNA-binding proteins （RBPs） play crucial roles in the post- transcriptional regulation via mRNA splicing, polyadenylation, sequence editing, transport, mRNA stability, mRNA localization, and translation. In this paper, four cDNAs of glycine-rich RNA-binding proteins （GR-RBPs）, named NtRGP-la, -lb, -2, and -3, were isolated from Nicotiana tabacum by RT-PCR analysis, and special emphases were given to the sequences alignment, phylogenetic analysis and gene expression. Sequences alignment revealed minor difference of cDNA sequences, but no difference of deduced proteins between N. sylvestris and N. tabacum. Phylogenetic alignment revealed that four cDNAs in tobacco were clustered into two different groups. NtRGP-2 and -3 were evolutionarily closest to Arabidopsis GR-RBPs genes and related to animal GR-RBPs genes, while NtRGP-la and -lb were closest to Gramineae GR-RBPs genes. The expression analyses of these four NtRGPs in response to different abiotic stresses revealed the similar expression pattern. Moreover, the four NtRGPs, especially NtRGP-la and NtRGP-3, were strongly induced by stresses including water, wound, cold, and high temperature, weakly induced by PEG, drought and SA, while reduced by NaC1 and unaffected by ABA treatment. The fact that all of these abiotic stresses included in our experiments affected the water balance and resulted in osmotic stress on cellular level, suggests that NtRGPs in tobacco should be a family of crucial osmosis-related proteins, and may play a key role in signal transduction with ABA-independent pathway under abiotic stresses.

Genome-wide identification and expression analysis of NtbHLH gene family in tobacco(Nicotiana tabacum)and the role of NtbHLH86 in drought adaptation

The bHLH transcription factors play pivotal roles in plant growth and development,production of secondary metabolites and responses to various environmental stresses.Although the bHLH genes have been well studied in model plant species,a comprehensive investigation of the bHLH genes is required for tobacco with newly obtained high-quality genome.In the present study,a total of 309 NtbHLH genes were identified and can be divided into 23 subfamilies.The conserved amino acids which are essential for their function were predicted for the NtbHLH proteins.Moreover,the NtbHLH genes were conserved during evolution through analyzing the gene structures and conserved motifs.A total of 265 NtbHLH genes were localized in the 24 tobacco chromosomes while the remained 44 NtbHLH genes were mapped to the scaffolds due to the complexity of tobacco genome.Moreover,transcripts of NtbHLH genes were obviously tissue-specific expressed from the gene-chip data from 23 tobacco tissues,and expressions of 20 random selected NtbHLH genes were further confirmed by quantitative real-time PCR,indicating their potential functions in the plant growth and development.Importantly,overexpressed NtbHLH86 gene confers improve drought tolerance in tobacco indicating that it might be involved in the regulation of drought stress.Therefore,our findings here provide a valuable information on the characterization of NtbHLH genes and further investigation of their functions in tobacco.

Current Situations and Countermeasures of Organic Tobacco Development

Current situations of organic tobacco development at both home and abroad,indicating that organic tobacco is one of the innovation directions for sustainable,healthy,environmental protection and low carbon development of modern tobacco industry.On the basis of foreign cultivation technical system for organic agriculture,the cultivation technical system for organic tobacco is summed up as follows:first,keep the diversity and continuity of space and time;second,ensure closeness of nutrient cycle;third,improve self-regulatory system and protection ability of crops.Then,the development trend of organic tobacco is analyzed and corresponding measures are put forward:establish production base and assessment system for organic tobacco;establish technical system for production of organic tobacco;establish and perfect evaluation system for management,production and supervision of organic tobacco;strengthen popularization of production and concept of organic tobacco;improve management of organic tobacco purchase,industry commerce handover,and redrying.

Integrated Biological Control of Tobacco Bacterial Wilt (<i>Ralstonia solanacearum</i>) and Its Effect on Rhizosphere Microbial Community

Biological control agents and soil amendments have been applied to control tobacco bacterial wilt, but the mechanism is not well-known. In the present study, a field experiment was performed to investigate the soil physicochemical properties, disease index (DI) and disease incidence of tobacco bacterial wilt, and rhizosphere microbial community. The results show that the control efficacy of single application of antagonistic bacteria and calcium cyanamide was 46.43% and 51.92%, respectively. While the combined control efficacy of antagonistic bacteria and calcium cyanamide was 65.79%. Besides, the combined application of antagonistic bacteria and calcium cyanamide could increase soil pH, total N alkaline N, and exchangeable Ca, which were negatively associated with the microbial diversity, soil-borne pathogenic microorganisms, and incidence of tobacco bacterial wilt. Additionally, the combination of antagonistic bacteria and calcium cyanamide can improve the proportion of some antagonistic microbial species, and these antagonistic microbial species were inversely associated with the DI of tobacco bacterial wilt. In conclusion: The integrated measure may influence soil microbial communities through enhancing soil physicochemical properties and rebuild healthy soil microbial community structure to mitigate tobacco bacterial wilt. The current study presented valuable insights into the mechanisms enhancing soil health in the integrated measure.

Recent Advances on Key Enzyme Genes in Metabolic Pathways Related to the Synthesis of Aroma Compounds in Tobacco

This article summarized three main kinds of metabolic pathways related to the synthesis of aroma compounds in plants, concluded the roles and expres- sion patterns of key enzyme genes catalyzing the formation of major intermediate products in phenylpropanoid metabolic pathway, isoprene metabolic pathway and alkaloid biosynthetic pathway respectively, highlighted the latest developments of these key enzyme genes in tobacco, and accordingly proposed that in-depth study at the protein level and analysis of metabolic network interaction should be carried out in tobacco besides the expression regulation and transgenic crop improvement at the genetic level. Based on the above analysis, further improvement of tobacco aroma quality through metabolic engineering and its application prospect in agricultural production were prospected.

Control Effect and Cost Evaluation of Different Sex Pheromones and Trapping Lamps against Spodoptern litura,Helicoverpa assulta and Helicoverpa armigera in Tobacco

[ Objective] The aim was to study the control effect of different sex pheromones and trapping lamps against main pests in tobacco. [ Method] Control effect of sex pheromone of different matrix lures and Jiaduo trapping lamp against Spodoptern litura, Helicoverpa assulta and Helicoverpa armigera in tobacco in Teng- chong of Yunnan were determined and compared, and the control cast was evaluated. [Result] The use of insect sex pheromones and insecticidal light traps had certain effect against S. litura and H. armiger. The trapping effect of sex pheromone traps was better than that of Jiaduo trapping lamp, and the PVC matrix lure had better performance than rubber matrix lure, which had strongest capturing capacity, continuous control effect and significant effort against S. litura. The traps with different settled densities and hanging heights also had different trapping effect against S. litura and H. armiger, and the hanging height of 100 - 150 cm from ground was the best; as the cost was considered, the cast of the area with low density of traps was the lowest, which was reduced by over 44% than conventional chemical control area. [ Conclusion] It is safe and effective to use sex pheromone and insecticidal light traps to control S. litura and H. armigera, and it is a green environmental protection biological physical control technology, having extended application prospect in large area.

Effects of Different Flue-curing Technologies on Submicroscopic Structure of Flue-cured Tobacco Leaves

[ Objective] This study aimed to compare the effects of low-temperature low-humidity tobacco flue-curing technology, moderate-temperature moderate- humidity tobacco flue-curing technology and moderate-temperature high-humidity tobacco flue-curing technology on submicroscopic structure of flue-cured tobacco leaves to provide theoretical basis for tobacco flue-curing. [ Method] Middle leaves of tobacco cuhivar K326 were collected in Pengshui County of Chongqing City for flue-curing experiment using three flue-curing technologies. Leaf samples were collected regularly in the flue-curing process, to investigate the submicroscopic structure of flue-cured tobacco leaves. [ Result] Morphology changes and structural rupture of chloroplasts occurred at different time during three flue-curing proces- ses. In low-temperature low-humidity flue-curing process, morphology changes and structural rupture of chloroplasts occurred late but rapidly; in moderate-tempera- ture moderate-humidity flue-curing process and moderate-temperature high-humidity flue-curing process, morphology changes and structural rupture of chloroplasts occurred early but slowly. Among these three flue-curing processes, the speed of changes in mitochondria morphology, cristae number and membrane rupture pres- ented an upward order of low-temperature low-humidity flue-curing process 〈 moderate-temperature high-humidity flue-curlng process 〈 moderate-temperature moderate-humidity flue-curing process. In low-temperature low-humldity flue-curing process, starch granules in chloroplasts ruptured after flue-curing for 36 -48 h ; in moderate-temperature moderate-humidity flue-curing process, starch granules in chloroplasts ruptured after flue-curing for 24 - 36 h; in moderate-temperature high-humidity flue-curing process, starch granules in chloroplasts ruptured after flue-curing for 12 - 24 h. [ Conclusion ] Using low-temperature low-humidity flue- curing technology could prolong the maintenance duration of the submicroscopic structure integrity of flue-cured tobacco leaves, which was conducive to fully decom- posing and transforming substances in tobacco leaves and obtaining high-quality flue-cured tobacco leaves.

Effects of Different Flue-curing Technologies on Microscopic Structure of Flue-cured Tobacco Leaves

[Objective] This study aimed to compare the effects of Chinese quality-improving fragrunce-increasing tobacco flue-curing technology, Chinese three- stage tobaeeo flue-curing technology and Zimbabwean tobaceo flue-euring technology on microscopie structure of flue-cured tobacco leaves to provide theoretical basis for tobacco flue-curing. [ Method ] Middle leaves of tobacco cultivar K326 were collected in Pengshui County of Chongqing City for flue-curing experiment using three flue-curing technologies. Leaf samples were collected regularly in the flue-curing process, to investigate the microscopic structure of flue-cured tobaceo leaves. [ Result] During three flue-curing processes, leaves, palisade tissues and sponge tissues shrank gradually. Three flue-euring processes exhibited significant differ- ences in the peak of tissue shrinkage ： microscopic structure of flue-cured tobacco leaves in Chinese three-stage tobacco flue-curing process shrank earliest, follower by Chinese quality-improving fragrance-increasing tobacco flue-curing process; flue-eured tobacco leaves in Zimbabwean tobacco flue-curing process presented the latest shrinkage. At 84 h post-curing, leaf thickness in three flue-curing processes showed a descend order of Chinese three-stage tobacco flue-curing process 〉 Chinese quality-improving fragrance-increasing tobacco flue-curing process 〉 Zimbabwean tobacco flue-curing process. Upper and lower epidermal cells in Zimb- abwean tobacco flue-curing process ruptured earlier than other two flue-curing processes; eventually, the majority of cells ruptured and mixed with palisade tissues and sponge tissues. In Chinese quality-improving fragranee-increasing tobacco flue-curing process, only a small number of epidermal cells in dried leaves ruptured. Among three flue-curing technologies, Zimbabwean tobacco flue-curing technology exhibited the greatest damage to epidermal cells, followed by Chinese three-stage tobaceo flue-curing technology; Chinese quality-improving fragrance-increasing tobacco flue-curing technology had the minimum damage to epidermal cells. Mese- phyll cross-section exhibited significant morphological changes in stomata. To be specific, at 0 - 12 h post-curing, stomata of tobacco leaves closed with slightly prominent stamatal apparatuses on upper and lower epidermis; at 24 -72 h post-curing, stomata of tobaceo leaves changed gradually from opening to closure with significantly prominent stomatal apparatuses on upper and lower epidermis; at 84 h post-curing, stomata of tobacco leaves closed, and the majority of stomatal appa- ratuses were significantly prominent. In Chinese quality-improving fragrance-increasing tobacco flue-curing process, only a small number of epidermal ceils ruptured at 84 h pest-flue-curing; palisade tissues and sponge tissues shrank almost simultaneously. Significant gaps were observed between palisade tissues and between pal- isade tissues and sponge tissues. Chinese quality-improving fragrance-increasing tobacco flue-curing technology exhibited lower disorder level compared with other two flue-curing technologies. [ Conclusion] Chinese quality-improving fragrance-increasing tobacco flue-curlng technology was conducive to maintaining the micro- scopic structure integrity of flue-cured tobacco leaves and obtaining high-quality flue-cured tobacco leaves.

Detection and Analysis of Number of Ralstonia solanacearum in Soil before Winter Tillage in Fuzhou Tobacco-growing Area, Jiangxi Province

[Objective]The paper was to optimize the tobacco planting area in Fuzhou City and to prevent the outbreak of tobacco bacterial wilt in large area.[Method]At the end of 2017,soil samples were collected from plots planned to be planted with tobacco in the following year in Yihuang,Guangchang,Lichuan and Le’an counties.[Result]Among 352 plots,116 plots were infected by Ralstonia solanacearum,while 236 plots were free of the pathogen,and the infected plots accounted for 32.95% of total plots.Among them,75 plots exceeded the order of magnitudes of 103,accounting for 21.31% of total plots and 64.66% of infected plots.It is suggested that the plots with an order of magnitude above 103 should be pretreated with quicklime or purple soil,or conducted crop rotation,or seeds must be directly abandoned;the dosage of biocontrol agents should be increased in planting.The plots with an order of magnitude below 103 should be pretreated with quicklime or purple soil,and the dosage of biocontrol agents should be increased in planting.[Conclusion]The results provide reliable theoretical basis and data support for soil improvement and bacterial wilt control.

Screening, Identification and Biocontrol Effect of Antagonistic Streptomyces Strain Tra69 against Tobacco Bacterial Wilt

[Objective] The paper was to screen the biocontrol agents with good control effects against tobacco bacterial wilt. [Method] The strains with antagonistic activity against tobacco bacterial wilt were isolated from 36 copies of rhizosphere soil sample. The strain with best inhibition effect was identified, and carried out pot test and growth-promoting experiment. [Result] The strain with best inhibtion effect was Tra69, which was identified to be Streptomyces flavogriseus. The fermentation liquid of Tra69 had good control effect against Ralstonia solanacarum, and also had good growth-promoting effect on tobacco. [Conclusion] Tra69 was the biocontrol agent with excellent control effect against R. solanacarum, which could be further developed and used in biological control against tobacco diseases.