Eight Gram-negative, aerobic, motile with paired polar flagella and rod-shaped bacteria were isolated from six tobacco fields in Yunnan, PR China. 16S rRNA gene sequence analysis revealed that all the strains belonged to the genus Ralstonia. Among them, strain 22TCCZM03-6 had an identical 16S rRNA sequence to that of R. wenshanensis 56D2T, and the other strains were closely related to R. pickettii DSM 6297T (98.34–99.86%), R. wenshanensis 56D2T (98.70–99.64%), and R. insidiosa CCUG 46789T (97.34–98.56%). Genome sequencing yielded sizes ranging from 5.17 to 5.72 Mb, with overall G + C contents of 63.3–64.1%. Pairwise genome comparisons showed that strain 22TCCZM03-6 shared average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values above the species cut-off with R. wenshanensis 56D2T, suggesting that strain 22TCCZM03-6 is a special strain of the R. wenshanensis. Five strains, including 21MJYT02-10T, 21LDWP02-16, 22TCJT01-1, 22TCCZM01-4, and 22TCJT01-2, had ANI values >95% and dDDH values >70% when compared with each other. These five strains had ANI values of 73.32–94.17% and dDDH of 22.0–55.20% with the type strains of the genus Ralstonia individually, supporting these five strains as a novel species in the genus Ralstonia. In addition, strains 21YRMH01-3T and 21MJYT02-11T represent two independent species. They both had ANI and dDDH values below the thresholds for species delineation when compared with the type species of the genus Ralstonia. In strains 21YRMH01-3T and 21MJYT02-10T, the main fatty acids were summed features 3, 8, and C16:0; however, strain 21MJYT02-11T contained C16:0, cyclo-C17:0, and summed features 3 as major fatty acids. The main polar lipids, including diphosphatidylglycerol, phosphatidylglycerol, and phosphatidylethanolamine, were identified from strains 21YRMH01-3T, 21MJYT02-10T, and 21MJYT02-11T. The ubiquinones Q-7 and Q-8 were also detected in these strains, with Q-8 being the predominant quinone. Based on the above data, we propose that the eight strains represent one known species and three novel species in the genus Ralstonia, for which the names Ralstonia chuxiongensis sp. nov., Ralstonia mojiangensis sp. nov., and Ralstonia soli sp. nov. are proposed. The type strains are 21YRMH01-3T (=GDMCC 1.3534T = JCM 35818T), 21MJYT02-10T (=GDMCC 1.3531T = JCM 35816T), and 21MJYT02-11T (=GDMCC 1.3532T = JCM 35817T), respectively.

A Gram-negative, aerobic, motile with paired polar flagella and rod-shaped bacterium strain (56D2T) was isolated from tobacco planting soil in Yunnan, PR China. Major fatty acids were C16  :  1 ω7c (summed feature 3), C16  :  0 and C18  :  1  ω7c (summed feature 8). The polar lipid profile of strain 56D2T consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, one unidentified aminophospholipid and one unidentified glycolipid. Moreover, strain 56D2T contained ubiquinone Q-8 as the sole respiratory quinone. 16S rRNA gene sequence analysis showed that strain 56D2T was closely related to members of the genus Ralstonia and the two type strains with the highest sequence identities were R. mannitolilytica LMG 6866T (98.36 %) and R. pickettii K-288T (98.22 %). The 16S rRNA gene sequence identities between strain 56D2T and other members of the genus Ralstonia were below 98.00 %. Genome sequencing revealed a genome size of 5.87 Mb and a G+C content of 63.7 mol%. The average nucleotide identity values between strain 56D2T and R. pickettii K-288T, R. mannitolilytica LMG 6866 T and R. insidiosa CCUG 46789T were less than 95 %, and the in silico DNA-DNA hybridization values (yielded by formula 2) were less than 70 %. Based on these data, we conclude that strain 56D2T represents a novel species of the genus Ralstonia, for which the name Ralstonia wenshanensis sp. nov. is proposed. The type strain of Ralstonia wenshanensis sp. nov. is 56D2T (=CCTCC AB 2021466T=GDMCC 1.2886T=JCM 35178T).

Three Gram-stain-negative, motile, with amphilophotrichous flagella, and rod-shaped bacteria (LJ1, LJ2T and LJ3) were isolated from lower leaves with black spots on flue-cured tobacco in Yunnan, PR China. The results of phylogenetic analysis based on 16S rRNA gene sequences indicate that all the strains from tobacco were closely related to the type strains of the Pseudomonas syringae group within the P. fluorescens lineage and LJ2T has the highest sequence identities with P. cichorii DSM 50259T (99.92 %), P. capsici Pc19-1T (99.67 %) and P. ovata F51T (98.94 %) . The 16S rRNA gene sequence identities between LJ2T and other members of the genus Pseudomonas were below 98.50%. The average nucleotide identity by blast (ANIb) values between LJ2T and P. cichorii DSM 50259T, P. capsici Pc19-1T and P. ovata F51T were less than 95 %, and the in silico DNA-DNA hybridization (isDDH) values (yielded by formula 2) were less than 70 %. The major fatty acids were C16  :  1ω7c and/or C16  :  1ω6c (summed feature 3), C16  :  0 and C18  :  1ω7c and/or C18  :  1ω6c (summed feature 8). The polar lipids profile of LJ2T consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, two unidentified phospholipids and one unidentified glycolipid. The predominant respiratory quinone was Q-9. The DNA G+C content of LJ2T was 58.4 mol%. On the basis of these data, we concluded that LJ2T represents a novel species of the genus Pseudomonas, for which the name Pseudomonas lijiangensis sp. nov. is proposed. The type strain of Pseudomonas lijiangensis sp. nov. is LJ2T (=CCTCC AB 2021465T=GDMCC 1.2884T=JCM 35177T).

Tobacco is one of the most significant non-food cash crops (Lu et al. 2020). In March 2022, cigar tobacco plants showing characteristic symptoms of vascular discoloration, stem rotting, leaf wilting and rotting were observed in Tengchong city (N 25°3'26″, E 98°25'6″) of Yunnan province, China (Fig. S1). The disease incidence was about 5% on cultivar Yunxue 6 in a 33-ha field. Infected stems were collected from Tengchong for pathogen isolation and 16S rDNA sequence analysis was performed as previously described (Lu et al. 2021). Sequence analysis showed that tobacco isolates (GenBank accession numbers: ON795108, ON795107 and ON795106) had an identical sequence with that of the species type strain of Pectobacterium versatile CFBP 6051T and shared the sequence identities of 99.55% and 99.47% with P. carotovorum DSM 30168T and P. parvum s0421T, respectively. Furthermore, phylogenetic analysis showed that tobacco strains were clustered with Pectobacterium versatile CFBP 6051T (Fig. S2a). In API assays, strain 22TC1 was positive for β-galactosidase activity, reduction of nitrates to nitrites, fermentation of glucose, hydrolysis of esculin and gelatin, assimilation of D-glucose, L-arabinose, D-mannose, D-mannitol, N-acetylglucosamine, malic acid and trisodium citrate; positive for the enzymatic substrates of alkaline phosphatase, leucine arylamidase, acid phosphatase, naphthol-AS-BI-phosphohydrolase, α-galactosidase, β-galactosidase and α-glucosidase. Furthermore, the average nucleotide identity (ANI) analysis (Richter et al. 2015) showed that strain 22TC1 (GenBank accession number: JAMWYQ000000000) had the highest ANIb score of 96.76% and ANIm value of 97.19% with P. versatile CFBP 6051T. Similarly, in silico DNA-DNA hybridization (isDDH) value was 74.5% compared to P. versatile CFBP 6051T, isDDH values were 35.5-63.7% with the other Pectobacterium species, which below the 70% threshold value for species delineation (Meier-Kolthoff et al. 2021). The phylogenomic analysis also showed that strain 22TC1 was clustered with the species type strain of P. versatile CFBP 6051T. For pathogenicity tests, cell suspension with ten-fold dilution (approx. 1 x 108 CFU/ml) was injected into the leaf axils of two 2-month-old tobacco stems (cv. Yunyan 87). As a control, tobacco seedlings were inoculated with sterile distilled water. The plants were sealed in plastic bags and maintained in a growth chamber at 28°C for 2 d. The symptoms of water-soaked decay were observed within 24 h of inoculation. Whole-plant decay was at 2 days after injection. No symptoms were developed in the controls. Reisolation was performed on diseased stems and the identity of isolated bacteria was confirmed by PCR and sequencing of 16S rRNA. Similar results were obtained in two independent experiments. Based on the above-described data, the causal pathogen of stem rot on cigar tobacco in Tengchong was identified as P. versatile. To our knowledge, this is the first time that P. versatile is found to cause stem rot on tobacco. Pectobacterium species have been reported to cause seed-borne diseases on tobacco seedlings in the floating tray system and soil-borne diseases in tobacco fields (Wang et al. 2017; Xia and Mo 2007). Therefore, studying the possible transmission of the P. versatile to tobacco plants is necessary.

为明确云南省大理州烟叶烘烤变黄期叶柄和部分叶片霉变的病原菌,依据柯赫氏法则,采用组织分离法分离病原菌,经室内和烤房内验证致病性,结合形态学和多基因序列分析鉴定病原物种类,运用平板拮抗法和活体生测法筛选生防菌.结果表明,分离物的形态学与根霉属(Rhizopus sp.)真菌相似,其ITS序列与少根根霉菌(Rhizopus arrhizus.,异名Rhizopus oryzae)模式菌株CBS 112.07T序列一致性大于99％;基于内转录间隔区(ITS)、肌动蛋白(ACT)和翻译延伸因子1-α(TEF)的多基因序列系统发育分析也表明,病原菌与少根根霉菌亲缘关系最近.综合形态学和多基因序列分析结果,确定烤烟霉变病病原菌为少根根霉菌.通过平板对峙法筛选获得5株抑菌能力较强的拮抗菌,其中芽孢杆菌(Bacillus spp.)Z002和05-1205在烤房内的防治效果均在70％以上.

为明确种植密度和施氮量对烤烟烟气质量的影响,设置了两因素三水平的田间裂区试验,考察种植密度与施氮量及其交互作用(互作)条件下的烟叶烟气质量特征.结果表明:①种植密度对烟气总粒相物、水分、焦油量以及单支烟抽吸口数影响达到显著水平,相同施氮量条件下,烟叶烟气总粒相物、焦油量随着种植密度的增大(1100株/667 m2至1345株/667 m2)呈降低趋势,其中中下部烟叶规律明显.②施氮量对烟气水分、焦油量有显著影响,中上部烟叶烟气焦油量随施氮量的减少而降低.③种植密度与施氮量互作分析显示,对烟气特性指标变异的贡献率为种植密度>施氮量,二者的影响效应存在显著的互作关系.

通过同源克隆法获得烟草抗病基因同源序列(RGAs),为烟草抗病基因的筛选和相关研究提供帮助.基于抗病基因的NBS-LRR保守结构域,筛选并合成了3对简并引物,扩增烟草中的NBS-LRR类抗病基因.获得了4条与抗病基因具有高度同源性的NBS-LRR类烟草抗病基因同源序列(TRGA,登录号:MK634316,MK634317,MK634318,MK634319),目的片段大小均在500 bp左右;BLAST X分析表明,获得的4个烟草RGAs与已知RGAs具有高度相似性,氨基酸相似性为97％～100％;聚类分析将其分成2大类,包括TIR-NBS-LRR和non-TIR-NBS-LRR两类抗病基因,其编码氨基酸序列含有NBS保守区的典型特征基序.通过简并引物进行同源扩增是分离烟草RGAs的有效方法,可为进一步抗病基因筛选及抗病分子育种奠定基础.

为明确钾营养供应对烟碱生物合成的影响规律,采用定量PCR和气相色谱-质谱联用法,研究不同供钾量条件下,烟草叶片烟碱含量和根系腐胺N-甲基转移酶(PMT)与喹啉酸磷酸核糖基转移酶(QPT)的表达情况.结果 表明,低钾供应会增加烟叶的烟碱含量、促进根系PMT基因的表达;高钾供应对烟叶的烟碱合成和根系的PMT基因表达具有明显的抑制效应.低钾处理后再恢复正常钾供应水平,可显著降低由低钾供应对烟碱合成和PMT基因表达的促进作用.不同的供钾水平同样影响QPT基因的表达水平,但与烟碱积累量的变化不存在明显的相关性.因此,烟草植株的烟碱含量受供钾水平的影响,钾可能通过控制根系腐胺N-甲基转移酶基因的表达来影响烟叶中烟碱的积累.

为探究叶面营养对缺素烤烟光合色素及品质的影响,以K326为材料,在缺锌土壤上设置钾肥扣减处理,结合钾、锌叶面施用,比较不同处理光合色素、光合速率、烟叶产质量、物理特性、化学品质、评吸质量的差异.结果表明,缺锌土壤上扣减钾肥20％的处理烤烟株高、茎围和LAI最小,叶绿素a、叶绿素b、叶黄素含量及光合速率显著下降,产值显著降低;喷施锌肥促进了烟叶色素及光合速率的提高,经济效益明显,在扣减20％钾肥条件下叶面喷施钾肥2次,烟叶色素和光合能力提升显著,较常规处理增收766.3元/hm2,烟叶钾含量及评吸得分显著提高;而扣减钾肥条件下复合喷施钾、锌2次,烟叶农艺性状表现最优,光合能力显著增强,烟叶化学成分协调,钾含量提升明显,感官评吸得分最高,综合经济效益最佳,相对增收903元/hm2.表明叶面营养可有效缓解烤烟缺素带来的不利影响,促进烤烟生长发育和烟叶化学成分协调,有利改善烟叶品质,并提高烟叶产值.

[目的]充分分析德宏烟区种植的津巴布韦烤烟品种KRK26的烟叶品质特性,发挥其独特风格特征,提高德宏烟叶可用性.[方法]以云南德宏和津巴布韦2个烟区KRK26上、中部烟叶为材料,评价了KRK26烟叶的外观质量、物理特性、感官评吸质量,并用气相色谱-质谱联用仪(GC/MS)分析香味成分.[结果]与津巴布韦烟叶相比,德宏烟叶的成熟度略差、油分稍显不足,单叶重、叶面密度、身份和结构方面差于津巴布韦烟叶;两糖、烟碱含量和糖碱比显著高于津巴布韦烟叶,总氮含量显著低于津巴布韦烟叶,两者整体化学成分均处于较为适宜范围,协调性较好;德宏烟叶风格特征主要表现为清甜香韵,香气飘逸;津巴布韦烟叶则表现为焦甜香韵,香气沉溢.此外,由于Maillard反应产物含量上的差异,德宏KRK26烤烟品种焦甜香韵稍逊于津巴布韦烟叶.[结论]受生态条件影响,德宏KRK26烟叶整体品质弱于津巴布韦KRK26烟叶,且风格特征存在一定差异,可根据研究结果结合德宏当地实际情况适当调整农艺措施.

[目的]明确烤烟成熟期适宜的滴灌定额.[方法]通过控水试验研究烤烟打顶-成熟期不同滴灌定额(0.0、10.5、17.5、24.5和31.5 mm)对烤烟生长及水肥利用效率的影响.[结果]不同成熟期滴灌定额中,以24.5 mm(I3)处理烟株农艺性状相对较优,成熟期烟株茎和叶干物质生物量最大,氮素利用率和灌溉水利用率相对较高,烟叶钾氯比和氮碱比最为协调.与其他处理相比,I3处理烟株茎和叶的生物量分别增加了4.7％～16.4％和3.7％～18.3％,氮素利用率和灌溉水利用率分别增加了3.8～18.3个百分点和0.9％～9.4％,中部叶钾氯比提高了32.1％,氮碱比下降了32.4％.[结论]与其他滴灌定额相比,24.5 mm是该区域较为适宜的烤烟成熟期滴灌定额.

本研究通过探讨氮素对烤烟其他营养元素吸收利用的影响,从而为实现烤烟养分调控、营养均衡提供依据.试验采用裂区设计,主处理设3个施氮水平(5 g.N/株,7 gN/株,9gN/株),副处理设3个硝态氮比例(25％,50％,75％),测定并分析氮水平和硝态氮比例对烤烟钙(Ca)、镁(Mg)、铜(Cu)、锌(Zn)等其它营养元素累积分配的影响.分析显示:根系中的Ca、Mg、Zn的含量在不同的氮水平和硝态氮比例下差异不显著;氮水平显著或极显著影响烟叶中的Cu含量;硝态氮比例对烟叶中的Zn含量的影响达到显著或极显著水平;氮水平和硝态氮比例的交互作用对烟叶中的Ca、Cu、Zn含量的影响也达到显著或极显著水平.在相同的氮水平和硝态氮比例下,叶片中Ca、Mg、Cu、Zn等营养元素的分配率较高;施用的硝态氮比例相同,随着施氮量的增加,分配到叶片中的Ca、Mg、Cu、Zn等营养元素的比例均减少.因此,在烤烟施肥中,不仅要关注氮等大量营养元素对烟叶的影响,而且需关注氮元素与其它营养元素间的平衡.本研究为烟叶生产中肥料的合理施用与养分的调控、平衡提供技术支撑.

Aiming at the situation of frequent drought in late spring and early summer in southwest areas, this paper adopted the method of rain proof drought shed installation and carried out a pool-culture experiment with same irrigation quota but different irrigation times, taking Honghuadajinyuan (Hongda) with strong drought resistance andYunyan 87 (Yun 87) with weak drought resistance as materials. The paper also analyzed the effects of different drought stress on tobacco characteristics, such as expression of drought resistant gene, physiological-biochemical traits of drought resistance, pigment content of tobacco leaf, photosynthetic of tobacco leaf, etc.. The results showed that chlorophyll a, chlorophyll b, chlorophyll a + b, chlorophyll a/b, carotenoid, leaf water content, transpiration rate, stomatal conductance and net photosynthetic rate tended to decrease under drought stress. And intercellular carbon dioxide concentration, proline, superoxide dismutase activity, soluble sugar, malondialdehyde content, and relative expressions of NtSOD, NtPOD, NtCAT, NtP5 CS, NtLEA5, NtNCED1 tended to increase under drought stress. Membrane lipids of chloroplast was effected and photosynthetic pigment content of tobacco leaf was decreased under drought stress at root extending stage, which lead to net photosynthetic rate decreased by non-stomatal factors.The effects of drought stress on tobacco growth and development at root extending stage were mitigated by osmotic adjustment and free oxygen removal. The relative expressions of NtP5 CS, NtLEA5, NtNCED1, which regulated ABA and proline, were up-regulated under drought stress by raising proline content in tobacco leaf, and decreasing vacuole osmotic potential and leaf water loss. Meanwhile, the relative expressions of NtP5 CS, NtLEA5, NtNCED1 were up-regulated under drought stress by strengthening activities of antioxidant enzymes, and removing free oxygen produced by drought stress. Three major components were obtained by principal component analysis. The cumulative contribution rate reached 91.3％, of which proline, superoxide dismutase activity, soluble sugar, NtSOD, NtPOD, NtCAT, NtP5 CS and NtLEA5 were divided into the first major component; chlorophyll a, chlorophyll b, chlorophyll a+b, chlorophyll a/b and carotenoid were divided into the second major component; Net photosynthetic rate and leaf water content were divided into the third major component. The major component of drought resistance in Hongda gained 4.608 score, which was 40.08％ higher than that of Yun 87. These indicators could be used as the principal indicators to identify the drought resistance of tobacco at root extending stage when breeding drought-tolerant tobacco varieties. The second major component including photosynthetic pigment index and third major component including net photosynthetic rate and leaf water content could be used as the secondary indicators.

The natural anthocyanins extracted from purple sweet potato was used as a color-developing agent for the determination of molybdenum.In H2SO4 medium,a blue stable composition of MO (Ⅵ) with natural anthocyanins in presence of ascorbic acid was formed.Its maximum absorption is at the wavelength of 680 nm.Based on this reaction,a spectrophotometric method for the determination of MO (Ⅵ) was proposed.At the optimum conditions,Beer's law was obeyed with the mass concentration of MO (Ⅵ)in the range of 0.01 ～ 0.24 μg/mL.The linear regression equation A =4.136 3c(μg/mL) +0.004,correlation coefficient r =0.999 1 and the apparent molar absorptivity was 3.97×105 L/(mol·cm) at the wavelength of 680 nm.The limit of detection was 2.10× 10 3 μg/mL.The interferences of foreign ions were also investigated.The procedure has been used to determine trace molybdenum in beans samples,with the relative standard deviation of below 0.79％ and the average recovery of 98.6％～ 101.3％.Results obtained by this method were consistent with the results found by atomic absorption spectrophotometry.

[Purpose] The aim of this study was to understand the influence of nitrogen on the absorption of phosphorus (P),potassium (K) and chlorine (Cl).[Method] The effects of nitrogen application rate and nitrate nitrogen ratio on accumulation and distribution of other nutrients of fluecured tobacco were studied.A field experiment was carried out.[Results] The effects of nitrogen application rate and nitrate nitrogen ratio on the contents of P,K and Cl were different.The interaction of nitrogen application rate and nitrate nitrogen ratio had a significant effect on the P content in cutters.The change of the chlorine content in tobacco leaf had no effection the nitrate nitrogen ratio,mainly affected the nitrogen application rate.The influences of nitrogen application rate,nitrate nitrogen ratio and the interaction of them on the K content in tobacco leaves reached significant or extremely significant level.At the same nitrogen application rate and nitrate nitrogen ratio,the allocation rate of P in leaves was higher,but the allocation rate of Cl was higher in stem,lower in root.Applying the same proportion of nitrate nitrogen,with the increase of nitrogen application,the allocation rate of P,K and Cl were reduced.[Conclusion] In tobacco production,it is necessary to pay attention to balance between and nitrogen fertilizer other nutrient elements.

Tyrosinase is a type-3 copper enzyme that is widely distributed in plants, fungi, insects, and mammals. Developing high potent inhibitors against tyrosinase is of great interest in diverse fields including tobacco curing, food processing, bio-insecticides development, cosmetic development, and human healthcare-related research. In the crystal structure of Agaricus bisporus mushroom tyrosinase, there is an oxygen atom bridging the two copper ions in the active site. It is unclear whether the identity of this bridging oxygen is a water molecule or a hydroxide anion. In the present study, we theoretically determine the identity of this critical bridging oxygen by performing first-principles hybrid quantum mechanics/molecular mechanics/Poisson-Boltzmann-surface area (QM/MM-PBSA) calculations along with a thermodynamic cycle that aim to improve the accuracy. Our results show that the binding with water molecule is energy favored and the QM/MM-optimized structure is very close to the crystal structure, whereas the binding with hydroxide anions causes the increase of energy and significant structural changes of the active site, indicating that the identity of the bridging oxygen must be a water molecule rather than a hydroxide anion. The different binding behavior between water and hydroxide anions may explain why molecules with a carboxyl group or too many negative charges have lower inhibitory activity. In light of this, the design of high potent active inhibitors against tyrosinase should satisfy both the affinity to the copper ions and the charge neutrality of the entire molecule.

Because of the characteristics of high flexibility and low cost,there are lots of advantages to use unmanned aerial vehicle (UAV)to collect the real-time information of field.In order to quickly monitoring the growth and development of crops grown in large scale field,a method for rapidly acquiring images of field-grown tobacco using quad-rotor UAV and digital image processing techniques was explored.The results show that under a relatively stable sky radiation condition,the images acquired with low flight height(e,g.20 m) can be used to produce rather high quality ortho-mosaic and 3D reconstruction.The images of individual field-grown tobacco plants were acquired using the vegetation segmentation algorithm based on decision tree to segment tobacco and non-vegetation part.The missing plant number of tobacco in individual plots was computed based on this algorithm and the results agree to the measured values well.Accordingly,this study provided a reliable way for rapidly and accurately accessing the growth and development of field-grown tobacco and studying plant phenotype in large scale.

种植模式显著影响土壤理化生物学性质,并与作物土传真菌病害的发生密切相关。试验选择云南省具有代表性的红壤,设置烤烟-休闲-玉米（T-B-M）、烤烟-油菜-玉米（T-C-M）、烤烟-油菜-水稻（T-C-R）和烤烟-苕子-水稻（T-V-R）等4种轮作模式,利用化学、酶学分析及454高通量测序技术,研究了土壤养分、酶活性及真菌群落结构,旨在为烤烟的合理轮作提供科学依据。经16a的不同轮作种植后,土壤p H变化于5.6—6.4之间,仍然适合种植水稻、玉米、油菜和烤烟等多种作物。在T-V-R处理的土壤中,烤烟产量、烟叶产值和上中等烟比例最高,有机质比原初提高45.11%,碱解氮、有效磷和微生物量碳氮显著增加,蔗糖酶、脱氢酶、脲酶、磷酸酶和过氧化氢酶活性也显著高于其它轮作模式,说明T-V-R改善了土壤生态环境,促进了微生物繁衍,数量增加,活性增强。土壤真菌的18S r DNA读数依次为13097（T-B-M）、11345（T-C-M）、12939（T-C-R）和13763（T-V-R）,分别代表530、378、395和581种（类）的真菌,由子囊菌门、担子菌门、接合菌门、壶菌门和尚待鉴定的真菌等构成,其中尚待鉴定的真菌属种和子囊菌门占绝大部分。在不同轮作处理的土壤中,前15种优势真菌的丰富度变化于29.46%—62.86%之间,优势菌株的相似性极低,说明土壤真菌的种群结构因轮作模式不同而异。T-V-R处理土壤中的真菌多样性指数最高,优势度指数最低,说明T-V-R轮作的土壤适合多种真菌的繁殖生长,种群数量增加。多种真菌共同存在,互相制约,可防止病原真菌过度繁殖,降低作物发生真菌病害几率。从作物产量和产值、土壤有机质、养分和真菌种群结构看,T-V-R优于其它3种轮作模式,值得推广应用。

AbstractIn order to explore the effects of plowing depth on yield and output of tobacco (Nicotiana tabacum L.) leaf, a field experiment was conducted, and soil physical characteristics and water content, spatial distribution of flue-cured tobacco root system as well as yield of tobacco were investigated. A flue-cured tobacco variety of ‘K326’ was planted with plowing depths of 20 cm (GS20, conventional tillage depth, CK), 30 cm (GS30) and 40 cm (GS40) in 2015 growing season, respectively. Leaf area and soil water content of 0-60 cm were measured after 30 days (rosette stage), 45 days (early vigorous growing stage), 60 days (later vigorous growing stage) and 75 days (early maturing stage) of transplant. Soil bulk density, total porosity, capillary porosity and non-capillary porosity after 54 day of transplant (vigorous growing stage) were investigated. Special distribution of root fresh weight after 65 days of transplant (squaring stage) was investigated too. The results showed that deep plowing had positive effect on soil structure, soil water storage, spatial distribution of flue-cured tobacco root system finally enhanced the yield and output. The deep plowing significantly decreased soil bulk density, increased soil total porosity, and capillary porosity at 20-40 cm subsurface soil layer. Compared to CK (G20), GS30 and GS40 decreased soil bulk density by 8.4% and 9.4%, increased soil total porosity by 15.6% and 13.1%, and increased soil capillary porosity by 25.8% and 24.8%, respectively. The deep plowing with depths of 30 cm and 40 cm significantly increased soil moisture content at 0-20 cm surface soil layer at rosette stage and at 20-40 cm subsurface soil layer at vigorous growing and maturing stages compared to those under GS20. Furthermore, the deep plowing not only significantly increased flue-cured tobacco root weight but also promoted the root content and proportion in deep soil. Root fresh biomass weight under GS30 and GS40 was 31.2% and 89.2% higher than that under GS20, respectively. Root depth index under GS30 and GS40 was 7.6% and 4.5% higher than that under GS20, respectively. In addition, tobacco leaf yield increased by 7.0% and 27.3%, average price increased by 1.8% and 6.2%, the ratio of the first-class tobacco increased by 10.4% and 24.4%, and the output value increased by 9.0% and 35.1% under GS30 and GS40 than those under GS20, respectively. There was significant difference between GS40 and GS20. The results showed that the improved soil physical characteristics, e.g., bulk density, total porosity and capillary porosity under deep plowing could increase soil moisture content at plough layer which benefited tobacco seedling growth, and lead to an optimization of the horizontal and vertical distribution of tobacco root system. A strong root system under deep plowing directly strengthened the growth of over-ground part of tobacco. Finally the yield and output value of tobacco leaf were increased.

Fast and non-destructive measurements of tobacco leaf pigment contents by spectroscopy in situ in the field has great significance in production guidance for nutrient diagnosis and growth monitoring of tobacco in vegetative growth stage, and it is also very important for the quality evaluation of tobacco leaves in mature stage. The purpose of this study is to estimate the chlorophyll and carotenoid contents of tobacco leaves using tobacco leaf spectrum collected in the field. Reflectance spectrum of tobacco leaves in vegetative growth stage and mature stage were collected in situ in the field and the pigment contents of tobacco leaf samples were measured in this study, taking the tobacco leaf samples collected in each and both stages as modeling sets respectively, and using the methods of support vector machine (SVM) and spectral indice to establish the pigment content estimation models, and then compare the prediction performance of the models built by different methods. The study results indicated that the difference of estimation performance by each stage or mixed stages is not significant. For chlorophyll content, SVM and spectral indice modeling methods can both have a well estimation performance, while for carotenoid content, SVM modeling method has a better estimation performance than spectral indice. The coefficient of determination and the root mean square error of SVM model for estimating tobacco leaf chlorophyll content by each stage were 0.867 6 and 0.014 7, while the coefficient of determination and the root mean square error of SVM model for estimating tobacco leaf chlorophyll content by mixed stages were 0.898 6 and 0.012 3; The coefficient of determination and the root mean square error for estimating tobacco leaf carotenoid content by each stage were 0.861 4 and 0.002 5, while the coefficient of determination and the root mean square error of SVM model for estimating tobacco leaf carotenoid content by mixed stages were 0.839 9 and 0.002 5. The innovation point of this study is that on the basis of support vector machine and spectral indice, models established by each stage and mixed stages for estimating the pigment contents of tobacco leaf samples can provide scientific basis and technical support for quality control of tobacco leaf production in field and the ensurance of tobacco leaf recovery quality.