Lipopolysaccharides of plant-growth promoting Pseudomonas sp. strain WCS417r induce resistance in carnation to Fusarium wilt

The numbers of diseased plants could significantly be reduced when microconidia ofFusarium oxysporum f. sp.dianthi were inoculated into the stem and viable-, heat-killed cells or purified LPS of the bacteriumPseudomonas sp. strain WCS417r were applied to the roots. Because the competition betweenF. o. dianthi and the bacterium could be excluded, the disease suppression seems to be due to an induced resistance. Accumulation of phytoalexins was found in the stem segments. No accumulation of these compounds was found when the plants were bacterized but noninfected. It is concluded that cell surface components present in the lipopolysaccharides of the bacterium are the inducing factors.Increased peroxidase activity could be measured in root washes and root extracts after only bacterial preparations were added. No significant differences in peroxidase activity were found in stem extracts. The possible role of increased peroxidase activity in suppression of Fusarium wilt in carnation is discussed.     

Implication of Systemic Induced Resistance in the Suppression of Fusarium Wilt of Tomato by Pseudomonas fluorescens WCS417r and by Nonpathogenic Fusarium oxysporum Fo47

Fluorescent pseudomonads and nonpathogenic Fusarium oxysporum have been shown to suppress fusarium wilts. This suppression has been related to both microbial antagonism and induced resistance.The aim of the present study was to assess the relative importance of systemic induced resistance in the suppression of fusarium wilt of tomato in commercial-like conditions by a reference strain of each type of microorganism (P. fluorescens WCS417r and nonpathogenic F. oxysporum Fo47). The spatial separation of the pathogen and the biocontrol strains excluded any possible microbial antagonism and implicated the involvement of the systemic induced resistance; whereas the absence of any separation between these microorganisms allowed the expression of both mechanisms. Since systemic induced resistance has often been associated with the synthesis of PR-proteins, their accumulation in tomato plants inoculated with WCS417r or with Fo47 was determined.The analysis of the results indicates that the suppression of fusarium wilt by P. fluorescens WCS417r was ascribed to systemic induced resistance without any detection of the PR-proteins tested (PR-1 and chitinases). In contrast, the suppression achieved by nonpathogenic F. oxysporum Fo47 appeared to be mainly ascribed to microbial antagonism but also to a lesser extent to systemic induced resistance. This induced resistance could be related to the accumulation of PR-1 and chitinases.The possible relationship between the ability of Fo47 to suppress fusarium wilt more efficiently than WCS417r and its ability to show both mechanisms is discussed.     

Reductive detoxification of the acetophenone skeleton of the carnation phytoanticipin by Fusarium oxysporum f.sp. dianthi

The skeleton of the carnation phytoanticipin, acetophenone, was detoxified by Fusarium oxysporum f.sp. dianthi , the main fungal parasite of carnation. This process consisted of the reduction to ethanol of the acetyl group, leading to the formation of phenylethanol, which has lower fungitoxic activity than the parent molecule. The conversion took place through the activity of an adaptive fungal oxidoreductase, which was NADH-dependent and was released by the fungus as two enzymatic forms within the culture substrate in the presence of acetophenone. Reduction was stereospecific and gave rise to only one of the two possible enantiomeric forms.     

Control of Fusarium wilt in melon by the fungal endophyte,Cadophora sp.

Two soil-borne fungal endophytes almost completely suppressed the effects of a post-inoculated and virulent strain of Fusarium oxysporum f. sp. melonis when inoculated to axenically reared melon seedlings in Petri dishes. They were identified as Cadophora sp. on the basis of ITS 1–5.8S rDNA–ITS 2 sequences and morphological characters and obtained from the roots of Chinese cabbage grown as bait plants in a mixed soil made up of samples from different forest soils from Alberta and British Columbia, Canada. Hyphae of Cadophora sp. grew along the surface of the root and colonized root cells of the cortex and reduced the ingress of the Fusarium pathogen into adjacent cells. Melon seedlings pre-inoculated with Cadophora sp. were also grown in soil amended with the different N sources, nitrate or the amino acids leucine and valine, and glucose (final C:N ratio?=?10:1). After 4 weeks, these seedlings were transplanted into the field and disease symptoms were assessed. Only the endophyte-inoculated seedlings treated with valine could effectively inhibit the development of Fusarium wilt in two plots and reduced disease symptom development by 43 and 62 %.     

生防菌株B-3对辣椒枯萎病的防治及其鉴定

为了明确生防菌株B-3对辣椒枯萎病的防效及其分类地位,采用管碟法测定了生防菌株B-3对辣椒枯萎病菌的抑制作用,考察了其对辣椒枯萎病的防效,并采用表型特征培养观察法、生理生化测定法和16SrDNA序列分析法对菌株B-3进行了鉴定。结果表明,生防菌株B-3的发酵液及其滤液对辣椒枯萎病菌均表现出较好的抑制作用,对辣椒枯萎病的盆栽与大田试验的防效都比较好,分别为73.6%和64.8%,显著优于100mg/L多菌灵。菌株B-3的形态与生理生化特性与枯草芽孢杆菌很接近,由16SrDNA序列分析的系统发育树发现,菌株B-3的序列与Bacillussubtilis菌株MO5单独构成一个分支,进化上的距离最近,由此可将其鉴定为枯草芽孢杆菌Bacillussubtilis。     

Siderophore-mediated competition for iron and induced resistance in the suppression of fusarium wilt of carnation by fluorescent Pseudomonas spp

The mechanisms of suppression of fusarium wilt of carnation by two fluorescentPseudomonas strains were studied.Treatments of carnation roots withPseudomonas sp. WCS417r significantly reduced fusarium wilt caused byFusarium oxysporum f. sp.dianthi (Fod). Mutants of WCS417r defective in siderophore biosynthesis (sid^–) were less effective in disease suppression compared with their wild-type. Treatments of carnation roots withPseudomonas putida WCS358r tended to reduce fusarium wilt, whereas a sid^– mutant of WCS358 did not.Inhibition of conidial germination of Fod in vitro by purified siderophores (pseudobactins) of bothPseudomonas strains was based on competition for iron. The ferrated pseudobactins inhibited germination significantly less than the unferrated pseudobactins. Inhibition of mycelial growth of Fod by bothPseudomonas strains on agar plates was also based on competition for iron: with increasing iron content of the medium, inhibition of Fod by thePseudomonas strains decreased. The sid^– mutant of WCS358 did not inhibit Fod on agar plates, whereas the sid^– mutants of WCS417r still did. This suggests that inhibition of Fod by WCS358r in vitro was only based on siderophore-mediated competition for iron, whereas also a non-siderophore antifungal factor was involved in the inhibition of Fod by strain WCS417r.The ability of thePseudomonas strains to induce resistance against Fod in carnation grown in soil was studied by spatially separating the bacteria (on the roots) and the pathogen (in the stem). Both WCS417r and its sid^– mutant reduced disease incidence significantly in the moderately resistant carnation cultivar Pallas, WCS358r did not.It is concluded that the effective and consistent suppression of fusarium wilt of carnation by strain WCS417r involves multiple mechanisms: induced resistance, siderophore-mediated competition for iron and possibly antibiosis. The less effective suppression of fusarium wilt by WCS358r only depends on siderophore-mediated competition for iron.     

生防菌株SC11的鉴定、定殖及对棉花枯萎病防治效果研究

 通过生物学特性观察和16S rDNA基因序列分析鉴定菌株SC11为壮观链霉菌(Streptomyces spectabilis)。该菌可在棉花根际土壤以及棉花根部长期定殖,30 d的定殖密度分别为1.38×10⁵ CFU/g和2.95×10³ CFU/g。2011年和2012年的大田防治试验显示,SC11菌粉对棉花枯萎病防效分别为42.51%和36.70%,与对照50%多菌灵(WP)的防效相比无显著差异,施用90~150 d的防效分别显著高于多菌灵(P<0.05)。与清水对照相比,田间施用SC11菌粉棉花倒三叶面积显著提高52.6%,籽棉和皮棉产量分别增加21.9%和23.0%(P<0.05)。研究结果表明,壮观链霉菌SC11是一株对棉花枯萎病具有应用前景的生防菌株。     

Plant defence reactions against fusarium wilt in chickpea induced by incompatible race 0 of Fusarium oxysporum f.sp. ciceris and nonhost isolates of F. oxysporum

Germinated seeds of 'kabuli' chickpea cv. ICCV 4 were inoculated with a conidial suspension of the incompatible race 0 of Fusarium oxysporum f.sp. ciceris (Foc) or of nonhost F. oxysporum resistance 'inducers', and 3 days later were challenged by root dip with a conidial suspension of highly virulent Foc race 5. Prior inoculation with inducers delayed the onset of symptoms and/or significantly reduced the final amount of fusarium wilt caused by race 5. However, the extent of disease suppression varied with the nature of the inducing agent; the nonhost isolates of F. oxysporum were more effective at disease suppression than the incompatible Foc race 0. Inoculation with the inducers gave rise to synthesis of maackiain and medicarpin phytoalexins in inoculated seedlings; these did not accumulate in plant tissues but were released into the inoculum suspension. Inoculation with inducers also resulted in accumulation of chitinase, β-1,3-glucanase and peroxidase activities in plant roots. These defence-related responses were induced more consistently and intensely by nonhost isolates of F. oxysporum than by incompatible Foc race 0. The phytoalexins and, to a lesser extent, the antifungal hydrolases, were also induced after challenge inoculation with Foc race 5. However, in this case the defence responses were induced in both preinduced and noninduced plants infected by the pathogen. It is concluded that the suppression of fusarium wilt in this study possibly involved an inhibitory effect on the pathogen of preinduced plant defences, rather than an increase in the expression of defence mechanisms of preinduced plants following a subsequent challenge inoculation.     

Analysis of Defense-related Proteins in Stem Tissue of Carnation Inoculated with a Virulent and Avirulent Race of Fusarium oxysporum F.sp. Dianthi

The aim of this study was to learn more about the accumulation of defense-related proteins in stem tissue from carnation cultivar Pallas inoculated with 2 near-isogenic races, the avirulent race 1 and the virulent race 8 of Fusarium oxysporum f.sp. dianthi. Stem tissue was used, from which the epidermis, cortex and medulla were peeled off from the vascular cylinder. It appeared that chitinase activity was constitutively expressed in the intercellular fluids (IFs) of untreated leaves, stems and roots of carnation. The total chitinase activity in the IFs of stem tissue increased with time after inoculation. This increase was similar after inoculation with the virulent, the avirulent race and water. At least four chitinase isoenzymes, three acidic and one basic isoform, were detected in the IFs of inoculated plants. In contrast, total 1,3--glucanase activity was not detected in the IFs of untreated leaves, stems and roots. Furthermore, the increases in 1,3--glucanase activity in IFs of stem tissue were markedly higher in the compatible and incompatible interactions than in the water control, indicating that this activity is specially induced by elicitors common to both races 1 and 8 of Fusarium oxysporum f.sp. dianthi. Using an antiserum against 1,3--glucanase P3 of tomato, 2 bands were detected on immunoblots in the IFs of stem tissue inoculated with races 1 and 8. No bands were visible after inoculation with water. Total peroxidase activity increased with time in all combinations. One basic and one acidic peroxidase isoform were present in these IFs. Peroxidase activity in a cell wall fraction prepared from stem tissue was clearly higher, and its increase faster, than the activity in the soluble stem fraction. These increases were similar in the virulent, the avirulent race and the water control. The growth of the fungus Trichoderma viride was inhibited by the IFs obtained from stem tissue inoculated with the virulent and the avirulent race of Fusarium oxysporum f.sp. dianthi. However, the growth of Fusarium oxysporum f.sp. dianthi itself was not affected by these IFs.     

利用棉花体内非致病镰刀菌防治棉花黄萎病

从棉花铃内部分离到两株镰刀菌VL－1和VL－2。平板对峙法表明，VL－1和VL－2生长速度快，通过空间竞争和营养有效地抑制黄萎病的生长；并且能够抑制棉花黄萎菌微菌核的产生。温室生测结果表明，VL－1和VL－2对棉花黄萎病的相对防效分别达到87．9％和66．4％。安全性测试证明，这两株镰刀菌在棉花整个生育过程中不造成棉花的伤害，是非致病性镰刀菌。田间试验结果显示，在棉田第一次黄萎病高峰时，VL－1和VL－2对黄萎病的防效较理想，分别为51．5％和45．4％。     

Influence of chickpea genotype and Bacillus sp. on protection from Fusarium wilt by seed treatment with nonpathogenic Fusarium oxysporum

Seeds of kabuli chickpea cultivars ICCV 4 and PV 61 were treated with conidia of nonpathogenic Fusarium oxysporum isolate Fo 90105 suspended in methylcellulose (3 × 10⁶ conidia.seed^-1), or with methylcellulose alone, and sown in soil artificially infested with 500 or 1,000 chlamydospores.g^-1 of F. oxysporum f. sp. ciceris race 5. At an inoculum concentration of 500 chlamydospores.g^-1, seed treatment with Fo 90105 significantly increased the incubation period of the disease by 11 (ICCV 4) or 25 (PV 61) days, and reduced the final disease incidence, disease intensity and the standardized area under the curve of disease intensity over time. This protection from disease was higher and more consistent in PV 61 than in ICCV 4. However, it was annulled with an inoculum concentration of 1,000 chlamydospores.g^-1, except for the incubation period in PV 61 which was increased by 10 days. When ICCV 4 seeds were treated with Fo 90105 (3 × 10⁶ conidia.seed^-1) and/or Bacillus sp. isolate RGAF 51 (1 × 10⁷ cfu.seed^-1), then sown in infested soil, there was no influence by the Bacillus isolate on protection conferred by Fo 90105. However, the degree of protection by the nonpathogenic F. oxysporum was higher and more consistent when plants from treated seeds were grown in sterile sand for 6 days, then transplanted into infested soil.     

Stem canker and wilt of delphinium caused by Fusarium oxysporum f. sp. delphinii in Japan

Stem canker and severe wilt were observed on delphinium plants (Delphinium elatum) in Aomori Prefecture, Japan, in 2008. The fungus isolated from the diseased crown was identified as Fusarium oxysporum f. sp. delphinii on the basis of morphological characteristics, nucleotide sequences, and host range. The isolate induced similar stem canker and wilt symptoms in inoculated delphinium plants. We propose the name “stem canker and wilt” for the disease.     

Variation in susceptibility of lettuce cultivars to fusarium wilt caused by Fusarium oxysporum f.sp. lactucae

Lettuce cultivars adapted to Californian growing conditions were screened for resistance to fusarium wilt caused by Fusarium oxysporum f.sp. lactucae in order to determine if differences in susceptibility among currently grown cultivars might contribute to management of this disease. Based on a preliminary evaluation of 46 cultivars, eight that were among the most resistant of their horticultural type (iceberg, romaine or leaf) were selected for further testing. The relative susceptibility of these cultivars was assessed by: (i) root-dip inoculation, (ii) sowing seeds into infested potting mix and (iii) transplanting seedlings into an infested field. Evaluations of disease severity showed that both methods (i) and (ii) produced cultivar rankings that were significantly correlated with rankings from field trials [method (iii)]. Two romaine and two leaf cultivars were highly resistant to fusarium wilt (mean disease severity rating of ≤1·3 on a 1–4 scale) under all test conditions. Other romaine and leaf cultivars, however, were highly susceptible in root–dip tests, so there was no consistent association between cultivar type and susceptibility to fusarium wilt. Likewise, there was considerable variation in susceptibility to wilt among iceberg cultivars, but all were significantly more susceptible than the most resistant romaine and leaf cultivars.     

Interactions between Fusarium oxysporum f. sp. tracheiphilum and Meloidogyne spp. in Vigna unguiculata. 1. Effects of different inoculum densities on Fusarium wilt

The effects of chlamydosporesandconidia of Fusarium oxysporum f sp. tracheiphilum at different initial spore concentrations were compared in the wilt-susceptible cowpea cultivar California Blackeye No. 5 (CB5). In glasshouse experiments with one inoculum density of either Meloidogyne incognita or M javanica, chlamydospores resulted in greater incidence and severity of Fusarium wilt than conidia at the same inoculum densities. Wilt symptoms also increased on wilt-resistant cultivar CB3 as inoculum densities of M. javanica were increased. When three cultivars were infested with moderate or high densities of both F. o. tracheiphilum and M. javanica. only CB5 developed sere wilt at either inoculum density. The wilt-tolerant cultivar Grant had mild wilt symptoms in most plants at moderate inoculum densities, and a tenfold increase in inoculum did not increase wilt ratings. CB3. however, had higher incidence and severity of Fusarium wilt symptoms at high inoculum densities, although 60% of the plants survived for 9 weeks.     

绿色木霉菌T23对黄瓜枯萎病防治效果及其几种防御酶活性的影响

 本文通过生物测定的方法初步研究了绿色木霉菌T23分生孢子和厚垣孢子对黄瓜枯萎病防治效果及黄瓜幼苗几种防御酶活性的影响。结果表明:黄瓜幼苗经木霉菌处理后,病情指数由33.69分别降至13.12和10.28,经木霉菌处理的黄瓜体内与抗性反应相关的苯丙氨酸解氨酶(PAL)、过氧化物酶(POD)、多酚氧化酶(PPO)及过氧化氢酶(CAT)活性有明显增加,其峰值分别为对照的2.75、2.49、2.42及15.84倍,说明生物防治过程中可能有木质素、植保素等抗性物质的参与。与分生孢子处理相比,木霉菌厚垣孢子处理的酶活高峰出现得晚,但酶活峰值高。     

青枯病的化学与生物防治研究进展

本文阐述了近年来在植物细菌性青枯病化学和生物防治研究方面所取得的进展。首先介绍了普通化学药剂和抗生素及植物生长调节剂等防治青枯病的新近应用，作用效果和防治特点；然后回顾了应用无致病力青枯菌菌株，拮抗细菌，菌根和基因工程技术进行生物防治的研究情况；最后对化学和生物防治的有关问题及应用前景进行了讨论。     

Evaluation of plant growth-promoting rhizobacteria for biological control of pythium root rot of cucumbers grown in rockwool and effects on yield

Three strains ofPseudomonas fluorescens (63-49, 63-28, and 15), one strain ofPseudomonas corrugata (13) and one strain ofSerratia plymuthica (R1GC4) were tested on rockwool-grown cucumbers for their ability to reduce Pythium root-rot caused byPythium aphanidermatum. These strains were previously selected for biocontrol ability from collections of >4000 bacteria. Strains 63-49 and 63-28 were tested on cucumber plants grown in rockwool in two replicatedPythium-inoculated trials conducted in British Columbia (B.C). Another inoculated, replicated trial was conducted in Quebec with all five strains. Cucumber yields (fruit number and weight) were measured over a ten-week harvest period. Strain 63-49 caused an early promotion of plant growth and increased cucumber yields at early harvests. No measurable effect ofPythium inoculation on disease development was observed in the Quebec trial, due to unfavourable cool weather. However, 63-49 significantly increased the total number of cucumbers (12%) and cucumber weight (18%), compared to the non-treated control. Strains 13, 15 and R1GC4 slightly increased the cumulative cucumber yields, but strain 63-28 had no effect. In the B.C. trial, inoculation withP. aphanidermatum reduced the number and weight of cucumbers by 27%. Treatments ofPythium-inoculated cucumbers with 63-49 significantly increased fruit number and weight by 18%, compared to thePythium-inoculated control. Strain 63-28 increased the cumulative number of cucumbers over time, compared to thePythium-inoculated control, but the increase was less than with 63-49. The use ofPseudomonas spp. in rockwool-grown cucumbers can increase yields, both in the presence and absence of Pythium root rot, and with variable seasonal conditions and disease pressures.     

哈茨木霉T-H-30菌株对黄瓜白粉病的防治效果及其促生作用

用哈茨木霉菌株T-H-30在黄瓜上进行促生作用及生物防治效果研究。结果表明,菌株T-H-30对黄瓜有明显的促生作用,能增加黄瓜的叶片数及藤蔓的长度,从而有效提高黄瓜的产量;菌株T-H-30对黄瓜白粉病具有良好的生物防治效果,可有效控制黄瓜白粉病在大田的发展,相对防效达69.9%～78.8%,且对供试植株安全。     

果园杂草对枯草芽胞杆菌控制石榴枯萎病的增效作用

测定枯草芽胞杆菌(Bacillus subtilis)在石榴园6种优势杂草胜红蓟(Ageratum conyzoides)、三叶鬼针草(Bidens pilosa)、大籽蒿(Artemisia sieversiana)、鸭跖草(Commelina communi)、牛筋草(Eleusine indica)、牛膝菊(Galinsoga parviflora)根部及根际土壤中的定殖动态,及杂草与枯草芽胞杆菌协同控制石榴枯萎病(Ceratocystis imbriata)的效果,为生防细菌的应用提供新的方法.结果显示,枯草芽胞杆菌在胜红蓟、三叶鬼针草、大籽蒿和鸭跖草的根部定殖能力都相对较强.在大籽蒿的根部定殖能力最强.而枯草芽胞杆菌只有在大籽蒿根际土中的可检测浓度持续到接种后的30 d.各种杂草结合枯草芽胞杆菌防治石榴枯萎病的结果表明,大籽蒿和胜红蓟表现卓越的增效作用.表明石榴园部分优势杂草可能通过促进枯草芽胞杆菌在其根系及根际中的定殖从而增强控制石榴枯萎病的作用.     

Inheritance of resistance in carnation against Fusarium oxysporum f.sp. dianthi races 1 and 2, in relation to resistance components

Four carnation cultivars, Novada (resistant to races 1 and 2 ofFusarium oxysporum f.sp.dianthi), Elsy (susceptible to race 1), Lena (susceptible to race 2) and Sam's Pride (susceptible to both races), were selfed and crossed. When three months old, the seedlings were inoculated via the roots or via the stems, after which wilting was recorded weekly according to a 5-point ordinal scale.Analyses were carried out on the proportions of diseased plants. For race 1 variation between the progenies could be described by means of general combining abilities only; GCA values were not affected by the inoculation method used. Also for race 2 GCAs were most important but the GCA values appeared different for the two inoculation methods. It is concluded that resistance to both races is inherited in an additive way.Indications for independently inherited root-specific resistance components (extravascular resistance) were only found with race 2. With both races, the ability to confine the pathogen at the infection site appeared the most important resistance component. Resistant progenies were also characterized by longer latent periods and lower wilting rates.Both race 1 and race 2 induced the accumulation of the phytoalexins dianthalexin and methoxydianthramide S, but race 2 induced higher amounts than race 1. The accumulation of phytoalexins was positively correlated to the resistance level of the progenies against the respective races. The progenies of the double-resistant cultivar Novada appeared to produce particularly high levels of phytoalexins.