调控基因gacA在荧光假单胞菌2P24防治土传病害中的作用

 Pseudomonas fluorescens 2P24分离自山东小麦全蚀病自然衰退土壤,该菌株能产生抗生素2,4-二乙酰基藤黄酚(2,4-diacetylphloroglucinol,2,4-DAPG)、氢氰酸,嗜铁素和蛋白酶,且抑菌谱广,可防治多种作物土传病害。本研究应用Tn5转座突变技术,获得1株产嗜铁素过量,同时不产生2,4-DAPG、HCN、蛋白酶、不能形成生物膜(biofilm)的突变菌株PM3390,其表现型与调控基因gacA的突变体表型相似。通过PCR介导的文库筛选方法,从2P24基因组文库中获得2个含有gacA基因的阳性克隆,进一步亚克隆,得到只含有完整gacA开放阅读框的1.2 kb片段,互补实验表明其能恢复突变菌株的多种缺失表型。生测结果表明,gacA-突变菌株与野生型2P24相比,对不同土传病害的生防效果均显著降低。以上结果证实gacA在2P24中具有整体水平的调控功能,并在2P24防治土传病害中起到重要的作用。     

Induced systemic resistance in arabidopsis thaliana against Pseudomonas syringae pv. tomato by 2,4-diacetylphloroglucinol-producing Pseudomonas fluorescens

Pseudomonas fluorescens strains that produce the polyketide antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG) are among the most effective rhizobacteria that suppress root and crown rots, wilts, and damping-off diseases of a variety of crops, and they play a key role in the natural suppressiveness of some soils to certain soilborne pathogens. Root colonization by 2,4-DAPG-producing P. fluorescens strains Pf-5 (genotype A), Q2-87 (genotype B), Q8r1-96 (genotype D), and HT5-1 (genotype N) produced induced systemic resistance (ISR) in Arabidopsis thaliana accession Col-0 against bacterial speck caused by P. syringae pv. tomato. The ISR-eliciting activity of the four bacterial genotypes was similar, and all genotypes were equivalent in activity to the well-characterized strain P. fluorescens WCS417r. The 2,4-DAPG biosynthetic locus consists of the genes phlHGF and phlACBDE. phlD or phlBC mutants of Q2-87 (2,4-DAPG minus) were significantly reduced in ISR activity, and genetic complementation of the mutants restored ISR activity back to wild-type levels. A phlF regulatory mutant (overproducer of 2,4-DAPG) had ISR activity equivalent to the wild-type Q2-87. Introduction of DAPG into soil at concentrations of 10 to 250 μM 4 days before challenge inoculation induced resistance equivalent to or better than the bacteria. Strain Q2-87 induced resistance on transgenic NahG plants but not on npr1-1, jar1, and etr1 Arabidopsis mutants. These results indicate that the antibiotic 2,4-DAPG is a major determinant of ISR in 2,4-DAPG-producing P. fluorescens, that the genotype of the strain does not affect its ISR activity, and that the activity induced by these bacteria operates through the ethylene- and jasmonic acid-dependent signal transduction pathway.     

The global regulator GacA of Pseudomonas fluorescens CHA0 is required for suppression of root diseases in dicotyledons but not in Gramineae

Pseudomonas fluorescens strain CHA0 suppresses various plant diseases caused by soil-borne fungi. The pseudomonad produces the antimicrobial metabolites 2,4-diacetylphloroglucinol (Phl), pyoluteorin (Plt) and hydrogen cyanide, which are important for disease suppression, as well as the siderophores pyoverdine (Pvd), salicylic acid (Sal) and pyochelin (Pch). In the current work, a derivative of CHA0 with a mutation in the global regulator gene gacA (GacA⁻), which is unable to produce Phl, Plt and HCN, failed to protect the dicotyledonous plants cress and cucumber against damping-off caused by Pythium ultimum . In contrast, the GacA⁻ mutant could still protect the Gramineae wheat and maize against damping-off mediated by the same strain of P. ultimum , and wheat against take-all caused by Gaeumannomyces graminis . However, the GacA⁻ mutant overproduced Pch and Pvd. To gain more insight into disease protection afforded by the GacA⁻ mutant, a GacA⁻ Pvd⁻ double mutant (strain CHA496) was constructed by gene replacement. Strain CHA496 overproduced Pch and Sal compared with CHA0 and protected wheat against P. ultimum and G. graminis , whereas cress and cucumber were not protected. Addition of FeCl₃ repressed Pch and Sal production by strain CHA496 in vitro and impaired the protection of wheat in soil microcosms. In conclusion, a functional gacA gene was necessary for the protection of dicotyledons against root diseases, but not for that of Gramineae. Results indicated also that Pch and/or Sal were involved in the ability of the GacA⁻ Pvd⁻ mutant of CHA0 to suppress root diseases in Gramineae.     

生防菌株2P24与CPF-10的鉴定及其生防相关性状的初步分析

 从山东省小麦根围土壤中分离到具有生防活性的细菌菌株2P24、CPF-10。通过对其16S rDNA序列同源性分析及生理生化测定鉴定为荧光假单胞菌(Pseudomonas fluorescens),其中菌株2P24为生物型I,CPF-10为生物型V。对这2株细菌的生防相关性状分析表明,二者均可产生多种抗菌物质,如2,4-二乙酰基间苯三酚(2,4-DAPG)、氢氰酸(HCN)、嗜铁素、蛋白酶等。平板对峙测定表明2株细菌对番茄青枯菌(Rastonia solanacearum)、棉花立枯丝核菌(Rhizoctonia solani)、棉花枯萎菌(Fusarium oxysporum)具有明显的拮抗作用。温室生测表明2P24对番茄青枯病的防效达63.0%。CPF-10达62.4%,且持续稳定。     

产抗菌素2,4-二乙酰基藤黄酚假单胞杆菌的分离及其防治沙打旺根腐病的室内测定

从山东、内蒙古、北京等地土壤中分离筛选出荧光菌 50 0 0余株 ,其中 1 2 0 0余株为抑制性荧光菌。经PCR检测 ,获得 73株 2 ,4 二乙酰基藤黄酚 (2 ,4 DAPG)产生菌。平板筛选结果表明 ,2 ,4 DAPG产生菌CPF 1 0和 2P8对沙打旺根腐病菌Sad1和Sad2均有较好的抑制效果 ,其中CPF 1 0的抑菌带宽分别为 5.0和 1 2 .0mm ;2P8抑菌带宽分别为 3 .5和 7.0mm。温室试验两次调查表明 ,CPF 1 0对沙打旺根腐病防治效果最好 ,达 63 .5%和 67.8% ;2P8防效也在 40 %左右 ,且均达到极显著水平。 2 ,4 DAPG产生菌可以显著促进沙打旺植株根系发育 ,CPF 1 0处理后地上部株高差异不显著 ,但鲜重和干重与对照相比有极显著的增加 ,说明两菌株菌剂处理可以促进植株生长。根部定殖结果表明 ,两菌株在沙打旺根部都有一定的定殖能力 ,在根表种群数量比较稳定 ,根内细菌数量在调查时间内呈逐渐上升的趋势     

Host Crop Affects Rhizosphere Colonization and Competitiveness of 2,4-Diacetylphloroglucinol-Producing Pseudomonas fluorescens

ABSTRACT Strains of Pseudomonas fluorescens producing the antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG) are biocontrol agents which play a key role in the suppressiveness of some soils against soilborne pathogens. We evaluated the effect of the host plant genotype on rhizosphere colonization by both indigenous and introduced 2,4-DAPG-producing P. fluorescens. First, population densities of indigenous 2,4-DAPG producers in the rhizospheres of alfalfa, barley, bean, flax, lentil, lupine, oat, pea, and wheat grown in a Fusarium wilt-suppressive Puget silt loam were determined. Population densities differed among the various crops and among pea cultivars, with lentil and oat supporting the highest and lowest densities of 2,4-DAPG producers, respectively. Second, to determine the interactions among 2,4-DAPG producers in the rhizosphere, a Shano sandy loam was inoculated individually and with all possible combinations of P. fluorescens Q8r1-96 (genotype D), F113 (genotype K), and MVP1-4 (genotype P) and sown to wheat or pea, and the rhizosphere population dynamics of each strain was monitored. All three strains were similar in ability to colonize the rhizosphere of wheat and pea when introduced alone into the soil; however, when introduced together in equal densities, the outcome of the interactions differed according to the host crop. In the wheat rhizosphere, the population density of strain F113 was significantly greater than that of Q8r1-96 in the mixed inoculation studies, but no significant differences were observed on pea. The population density of strain Q8r1-96 was greater than that of MVP1-4 in the mixed inoculation on wheat, but the opposite occurred on pea. In the wheat rhizosphere, the population of MVP1-4 dropped below the detection limit (log 3.26 CFU g(-1) of root) in the presence of F113; however, on pea, the population density of MVP1-4 was higher than that of F113. When all three strains were present together, F113 had the greatest density in the wheat rhizosphere, but MVP1-4 was dominant in the pea rhizosphere. Finally, eight pea cultivars were grown in soil inoculated with either MVP1-4 or Q8r1-96. The effect of the pea cultivar on rhizosphere colonization was dependent on the bacterial strain inoculated. Rhizosphere population densities of MVP1-4 did not differ significantly among pea cultivars, whereas population densities of Q8r1-96 did. We conclude from these studies that the host crop plays a key role in modulating both rhizosphere colonization by 2,4-DAPG-producing P. fluorescens and the interactions among different genotypes present in the same rhizosphere.     

Genetic Diversity of phlD from 2,4-Diacetylphloroglucinol-Producing Fluorescent Pseudomonas spp

ABSTRACT Fluorescent Pseudomonas spp. that produce 2,4-diacetylphloroglucinol (2,4-DAPG) have biocontrol activity against damping-off, root rot, and wilt diseases caused by soilborne fungal pathogens, and play a key role in the natural suppression of Gaeumannomyces graminis var. tritici, known as take-all decline. Diversity within phlD, an essential gene in the biosynthesis of 2,4-DAPG, was studied by restriction fragment length polymorphism (RFLP) analysis of 123 2,4-DAPG-producing isolates from six states in the United States and six other locations worldwide. Clusters defined by RFLP analysis of phlD correlated closely with clusters defined previously by BOX-polymerase chain reaction (PCR) genomic fingerprinting, indicating the usefulness of phlD as a marker of genetic diversity and population structure among 2,4-DAPG producers. Genotypes defined by RFLP analysis of phlD were conserved among isolates from the same site and cropping history. Random amplified polymorphic DNA analyses of genomic DNA revealed a higher degree of polymorphism than RFLP and BOX-PCR analyses. Genotypic diversity in a subset of 30 strains representing all the phlD RFLP groups did not correlate with production in vitro of monoacetylphloroglucinol, 2,4-DAPG, or total phloroglucinol compounds. Twenty-seven of the 30 representative strains lacked pyrrolnitrin and pyoluteorin biosynthetic genes as determined by the use of specific primers and probes.     

荧光假单胞菌2P24中phlF基因对抗生素2,4-二乙酰基间苯三酚产生的影响

Pseudomonas fluorescens2P24是分离自山东小麦全蚀病自然衰退土的1株生物防治菌株,产生抗生素2,4-二乙酰基间苯三酚(2,4-diacetylphloroglucinol;2,4-DAPG)是其主要防病机制。2,4-DAPG是由phlACBD基因簇合成,受多种调控因子调控。本研究用Tn5转座子插入技术,获得1株phlA基因转录增强的突变体,其突变基因为抗生素合成的负调控基因phlF。与野生菌相比,phlF基因的缺失突变体中phlA的转录增强约100倍,抗生素产量提高492倍。同时,菌株2P24的phlF缺失突变体对病原真菌的拮抗作用明显增强。但2,4-DAPG过量表达菌株对多种作物种子根生长有抑制作用。     

Effect of cold-water irrigation on bacterial wilt pathogen of tomato

Bacterial wilt caused by Ralstonia solanacearum is one of the most devastating bacterial diseases of plants worldwide. Management of bacterial wilt in tomato and other crops has been difficult, and so novel but easily implemented control methods are being sought. To evaluate the effect of cold-water irrigation on bacterial wilt of tomato, four treatments were used in which CF (chemically fertilized) soil and CF + FYM (chemical fertilizer + farmyard manure [FYM]) soil were inoculated with a bacterial suspension (R. solanacearum strain YU1Rif43) at 10⁶ colony forming units (CFU) g^?1 soil. Tomato seedlings were grown in Agri-pots in a plant growth chamber. The soil was irrigated with water that was kept at the same temperature in each treatment: 4, 10, 20, or 30°C. Incidence and severity of wilt, counting of the colonies of the culturable population of pathogen, and dry-mass and height of the plants were examined. After 45 days and in both kinds of soil, most of the plants had wilted in soil irrigated at 30°C. Wilt incidence was substantially reduced when transplanted seedlings were irrigated at lower temperatures (4–20°C). Survival of R. solanacearum was also reduced after being irrigated with water at lower temperatures, indicating that the reduced incidence of wilt was linked to reduced survival of the pathogen. Dry-mass and plant height were slightly higher under control conditions than in soils irrigated at lower temperatures. This study suggests that cold-water irrigation could significantly reduce bacterial wilt of tomato and have an adverse effect on survival of the wilt pathogen.     

植物疫苗鄂鲁冷特对番茄青枯病的田间防治效果

为了明确植物疫苗鄂鲁冷特对番茄育苗及其田间青枯病防治效果的影响,在番茄育苗基质中添加植物疫苗,测定处理后种苗株高、根系长度及出苗率;在田间种植共设疫苗袋装、沟施、浇灌及生防菌剂、化学农药和清水对照6个处理,对根系土壤的养分含量、植株的生物学性状及青枯病发病率进行研究。结果表明,植物疫苗处理分别能使番茄植株株高、根系长度和出苗率提高13.71%、68.20%和56.66%;疫苗袋装和沟施处理的番茄根系土壤有机质、全氮、全磷、全钾和交换性钙含量均显著高于其它处理;疫苗袋装、沟施和浇灌均能显著提高番茄植株的株高、花数和产量,其中疫苗袋装处理效果最好,番茄产量最高为99.55 t/hm~2,对不同生育期的平均防治效果最高为93.47%。表明植物疫苗鄂鲁冷特的应用能育出壮苗,降低青枯发病率,提高产量。     

荧光素酶标记无致病力青枯雷尔氏菌的生物学和定殖特性

为示踪青枯雷尔氏菌Ralstonia solanacearum无致病力菌株FJAT1458在番茄植株及根际土壤中的定殖特性,采用电击法对菌株FJAT1458进行荧光素酶(luciferase,LUC)基因标记,并于室内采用生测法测定标记菌株的生物学特性、遗传稳定性、致病力及在番茄植株和根际土壤中的定殖能力。结果表明,成功将luc基因整合至无致病力菌株FJAT1458染色体上,标记菌株FJAT1458-LUC发出强烈的荧光,且PCR扩增出1 612 bp的luc基因片段;与野生型菌株FJAT1458相比,标记菌株FJAT1458-LUC的生长明显滞后,培养8h之后标记菌株FJAT1458-LUC的OD_600nm值均小于野生型菌株FJAT1458;且标记菌株FJAT1458-LUC连续传代20次后菌体浓度显著增加,发光菌体比例显著降低,LUC活性和luc基因表达量均随着传代数增加而显著降低;标记前、后菌株FJAT1458的弱化指数分别为0.90和0.89,且接种番茄植株30 d均未引起植株发病。标记菌株FJAT1458-LUC能在番茄根际土壤、根及茎中定殖,定殖数量呈...     

青枯雷尔氏菌无致病力突变菌株的构建及其防效评价模型分析

 利用青枯雷尔氏菌(Ralstonia solanacearum)无致病力菌株防治番茄青枯病具有很好的应用潜力。作者通过分离筛选自然弱毒株、⁶⁰Co辐射诱变和EZ-Tn5插入诱变,分别获得3、12和40株青枯雷尔氏菌无致病力突变菌株。经盆栽番茄苗致病性检测,15 d后均未发病,证实均为无致病力青枯雷尔氏菌。进一步对番茄青枯病的防治试验表明,从番茄青枯病发病田块分离的无致病力突变菌株FJAT1458的防治效果最好,防效达100%。该菌株能定殖番茄植株根系土壤、根部和茎部,定殖数量均表现为“先增后减”的趋势,并且接种浓度越大、苗龄越小,定殖数量越大。从构建的防效模型可以看出,不同接种浓度条件下,植株发病率随时间变化符合的回归方程不同,相关系数R值也不同,接种浓度越大,R值越小。本研究获得的青枯雷尔氏菌无致病力突变菌株FJAT1458对番茄青枯病具有很好的防病效果。     

Specific Detection of Tomato Pathotype of Verticillium dahliae by PCR Assays

Verticillium dahliae Klebahn is the causal agent of tomato wilt disease. Isolates of V. dahliae can be classified based on pathogenicity to tomato, but the pathotypes are indistinguishable in morphology. We designed PCR primers for specific detection of isolates pathogenic to tomato (tomato pathotype) from the sequences of a pathotype-specific gene, vdt1. With the primer pair Tg5/Tc3, a PCR product (approximately 3.2 kb) specific to tomato pathotype was amplified from the genomic DNA of isolates. Using the primer pair, a tomato pathotype isolate was specifically detected from hypocotyls of inoculated tomato and eggplant. On the other hand, no amplification was observed from non-tomato pathotype isolates of V. dahliae, some other wilt pathogens of tomato and a healthy host plant. Therefore, the primer pair can be useful for pathotype-specific detection of V. dahliae as well as for diagnosis of wilt disease of tomato plant. Received 7 September 2001/ Accepted in revised form 3 December 2001     

Comparison of Three Methods for Monitoring Populations of Different Genotypes of 2,4-Diacetylphloroglucinol-Producing Pseudomonas fluorescens in the Rhizosphere

ABSTRACT Pseudomonas fluorescens strains producing the antibiotic 2,4-diacetylphloroglucinol (DAPG) have biocontrol activity against a broad spectrum of root and seedling diseases. In this study, we determined the effect of genotype on the ability to isolate and quantify introduced 2,4-DAPG producers from the rhizosphere of wheat using three different methods: traditional dilution plating on selective media, colony hybridization followed by polymerase chain reaction (PCR), and phlD-specific PCR-based dilution endpoint assay. Regression analysis of the population densities of 10 2,4-DAPG-producing P. fluorescens, representing five genotypes, determined by the three different methods demonstrated that the relationship was linear (P < 0.001) and the techniques were very similar (i.e., slopes equal to 1.0). The phlD-specific PCR-based assay had a slightly lower limit of detection than the other two methods (log 3.3 versus log 4.0 CFU/g of fresh root weight). With the colony hybridization procedure, we observed that the phlD probe, derived from strain P. fluorescens Q8r1-96, hybridized more strongly to colonies of BOX-PCR genotypes D (strains W2-6, L5.1-96, Q8r1-96, and Q8r2-96) and K (strain F113) compared with strains of genotypes A (Pf-5 and CHA0), B (Q2-87), and L (1M1-96 and W4-4). Colony hybridization alone overestimated the actual densities of some strains, thus requiring an additional PCR step to obtain accurate estimates. In contrast, population densities estimated for three of the bacterial treatments (strains CHA0, W2-6, and Q8r2-96) with the PCR-based assay were significantly (P < 0.041) smaller by 7.6 to 9.2% and 6.4 to 9.4% than population densities detected by the dilution plating and colony hybridization techniques, respectively. In this paper, we discuss the relative advantages of the different methods for detecting 2,4-DAPG producers.     

内生菌B47的定殖能力及其对番茄青枯病的防治作用

从番茄茎分离的内生枯草芽孢杆菌菌株B47对番茄青枯病有较好的防治作用,利用该菌株的抗链霉素突变菌株,研究其在土壤和番茄植株根、茎中的定殖能力及其对番茄青枯病的防治作用。结果表明,枯草芽孢杆菌菌株B47可在土壤和番茄植株中定殖。B47施到土壤中后的15~45天,其数量逐步增加,45天后,其数量逐步下降。B47在土壤中的定殖能力随土壤的种类和土壤的处理情况而异。施入菜地土后的第45天,B47在非灭菌土中的数量是9.91×105cfu/g土壤干重,而在灭菌土中的数量是9.84×107cfu/g土壤干重。接种后,番茄植株根和茎中的B47数量,从苗期到结果期逐渐增加,但到了成熟期呈下降趋势。B47和番茄青枯病菌混合施入土壤后,随B47的数量增加番茄青枯病菌的数量显著降低。当番茄植株根和茎中B47的含量分别为1.17×104cfu/g鲜重和3.33×104cfu/g鲜重时,接种番茄青枯病菌后的第20天,对番茄青枯病的防治效果达79.79%。     

抗不同生化型青枯菌的生防菌筛选鉴定及其活性分析

为更好地利用生防菌控制青枯病危害,从不同地区的土壤中分离到569株细菌菌株,筛选到3株对5种不同生化型青枯劳尔氏菌Ralstonia solanacearum具有较强拮抗活性的菌株,其中菌株BS2004的拮抗活性最强。以BS2004的菌悬液为对照,分别测定无菌滤液、蛋白酶K及高温热处理后拮抗物质抑菌活性的变化。结果显示,蛋白酶K及高温热处理后,该菌的抑菌活性显著降低,表明其主要抑菌成分为蛋白类物质。在设施栽培条件下用生防菌BS2004菌悬液处理番茄植株,能有效控制番茄青枯病的发生,防治效果达66.75%,同时还发现,重新分离得到的青枯菌菌体数明显受到生防菌的抑制。通过对BS2004的形态、生理生化特征、脂肪酸鉴定、16S rDNA序列等进行分析,该菌株被鉴定为解淀粉芽孢杆菌Bacillus amyloliquefaciens。     

Application of Rhizobacteria for Induced Resistance

This article provides a review of experiments conducted over a six-year period to develop a biological control system for insect-transmitted diseases in vegetables based on induced systemic resistance (ISR) mediated by plant growth-promoting rhizobacteria (PGPR). Initial experiments investigated the factors involved in treatment with PGPR led to ISR to bacterial wilt disease in cucumber caused by Erwinia tracheiphila. Results demonstrated that PGPR-ISR against bacterial wilt and feeding by the cucumber beetle vectors of E. trachiphiela were associated with reduced concentrations of cucurbitacin, a secondary plant metabolite and powerful beetle feeding stimulant. In other experiments, PGPR induced resistance against bacterial wilt in the absence of the beetle vectors, suggesting that PGPR-ISR protects cucumber against bacterial wilt not only by reducing beetle feeding and transmission of the pathogen, but also through the induction of other plant defense mechanisms after the pathogen has been introduced into the plant. Additional greenhouse and field experiments are described in which PGPR strains were selected for ISR against cucumber mosaic virus (CMV) and tomato mottle virus (ToMoV). Although results varied from year to year, field-grown tomatoes treated with PGPR demonstrated a reduction in the development of disease symptoms, and often a reduction in the incidence of viral infection and an increase in tomato yield. Recent efforts on commercial development of PGPR are described in which biological preparations containing industrial formulated spores of PGPR plus chitosan were formulated and evaluated for use in a transplant soil mix system for developing plants that can withstand disease attack after transplanting in the field.     

Visualization of <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> cells during biocontrol of bacterial wilt disease in tomato with <Emphasis Type="Italic">Pythium oligandrum</Emphasis>

The biocontrol agent Pythium oligandrum (PO) can suppress bacterial wilt caused by Ralstonia solanacearum (RS) in tomato. To understand the primary biocontrol mechanisms of bacterial wilt by PO, we pretreated tomato plants with sterile distilled water or preinoculated them with PO, followed by inoculation with RS, then observed PO and RS in fixed sections of tomato tissues using a confocal laser-scanning microscope and fluorescence labeling until 14 days after the inoculation with RS. Horizontal and vertical movement of RS bacteria was frequently observed in the xylem vessels of roots and stems of tomato plants (cv. Micro-Tom) that had not been inoculated with PO. In plants that were preinoculated with PO, the movement of RS was suppressed, and bacteria appeared to be restricted to the pit of vessels, a reaction similar to that observed in resistant rootstocks. PO colonization was mainly observed at the surfaces of taproots, the junctions between taproots and lateral roots, and the middle sections of the lateral roots. PO was not observed near wound sites or root tips where RS tended to colonize. However, RS colonization was significantly repressed at these sites in PO preinoculated plants. These observations suggest that the induction of plant defense reactions is the main mechanism for the control of tomato bacterial wilt by PO, not direct competition for infection sites.     

利用拮抗的Pseudomonas spp.和无致病力的P.solanacearum防治青枯病的研究

 从番茄、烟和木麻黄根围土壤中分离了606个Pseudomonas spp.菌株,94a和22a对番茄、烟和花生青枯病有一定效果。用番茄青枯菌和花生青枯菌通过Co⁶⁰辐射和紫外光诱变的无致病力菌株,25c、55b对番茄青枯病;45b对花生青枯病;107b对花生青枯病;有一些效果。但不够理想。试验结果证明从植物根围土壤筛选有拮抗作用的P.spp.有可能用于防治青枯病。     

Involvement of jasmonic acid signalling in bacterial wilt disease resistance induced by biocontrol agent Pythium oligandrum in tomato

When the biocontrol agent Pythium oligandrum (PO) colonizes the rhizosphere, it suppresses bacterial wilt disease in tomato (Solanum lycopersicum cv. Micro‐Tom) caused by Ralstonia solanacearum, and a homogenate of its mycelia exhibits elicitor activity, inducing an ethylene (ET)‐dependent defence response in Micro‐Tom. Since salicylic acid (SA) and jasmonic acid (JA) play an important role in plant defence responses to pathogens, the involvement of SA‐ and JA‐dependent signal transduction pathways in resistance to R. solanacearum was investigated in tomato roots treated with a mycelial homogenate of PO. Bacterial wilt disease was also suppressed in tomato cv. Moneymaker treated with the PO homogenate. However, the SA‐inducible PR‐1(P6) gene was not up‐regulated in either Micro‐Tom or Moneymaker. SA did not accumulate in homogenate‐treated roots in comparison with distilled water‐treated controls, even 24 h after inoculation. Induced resistance against R. solanacearum was not compromised in SA‐non‐accumulating NahG transgenic plants treated with the PO homogenate. On the other hand, the expression of the JA‐responsive gene for the basic PR‐6 protein was induced in both tomato cultivars treated with the PO homogenate. Furthermore, quantitative disease assays showed that the induced resistance against R. solanacearum was compromized in PO homogenate‐treated jai1‐1 mutant plants defective in JA signalling. These results indicated that the JA‐dependent signalling pathway is required for PO‐induced resistance against R. solanacearum in tomato.