Interaction between silicon amendment,bacterial wilt development and phenotype of Ralstonia solanacearum in tomato genotypes

Silicon amendment significantly reduced bacterial wilt incidence expressed as area under disease progress curve for tomato genotypes L390 (susceptible) by 26.8% and King Kong2 (moderately resistant) by 56.1% compared to non-treated plants grown in hydroponic culture. However, wilt incidence in silicon-treated plants of genotype L390 reached 100% at 13 days post-inoculation (dpi), while in genotype King Kong2, plant death was retarded by 6 days, with 20% reduction of final wilt incidence. Bacterial numbers were significantly lower in silicon-treated compared to non-treated plants in King Kong2 at 2 dpi in midstems and in all organs at 5 dpi, and in Hawaii 7998 (resistant) in all organs at 2 dpi. Differences between genotypes were obvious on midstem level (5 dpi), where bacterial populations were generally significantly lower compared to roots. Increased tolerance was observed in genotypes L390 and King Kong2 with silicon treatment.Silicon accumulated in roots and was low in stems and leaves. Inoculation with Ralstonia solanacearum did not significantly affect silicon uptake and distribution. Negative correlations between root silicon content and bacterial numbers of midstems in genotypes Hawaii 7998 and King Kong2 suggested an induced resistance. Indications for an influence of host genotype and silicon treatment on the phenotypic conversion of R. solanacearum strain To-udk2-sb from fluidal to non-fluidal colonies in planta were observed.This is the first report on the effect of silicon on a bacterial disease and in a silicon-non-accumulator plant.     

Effect of calcium nutrition on resistance of tomato against bacterial wilt induced by Ralstonia solanacearum

This study investigated the effect of calcium nutrition on tomato bacterial wilt caused by Ralstonia solanacearum and the regulation of resistance mechanisms. Plants cultured in nutrient solution with calcium concentrations of 0.5, 5.0, and 25.0 mM, were inoculated with R. solanacearum by the root dip method. Severity of disease development, Ca concentration in tomato root and shoot tissues, hydrogen peroxide (H₂O₂) concentration, peroxidase (POD, EC 1.11.1.7) and polyphenol oxidase (PPO, EC 1.10.3.2) in tomato leaves were analyzed. Disease severities of low, medium and high Ca treatments were 100 %, 77.1 % and 56.8 % respectively. Plant growth in high Ca treatment was significantly better than those in low Ca treatment in height, stem diameter and biomass. Tomato plants absorbed significantly more Ca in roots and shoots as the level of Ca in the nutrient solution increased. In addition, H₂O₂ level in high Ca treatment rose faster and reached a higher peak with 10.86 μM gFW^?1(31.32 % greater than medium Ca plants). The activities of POD and PPO also have a greater increase in high Ca treatment with 99.09 U gFW^?1 and 107.24 U gFW^?1 compared to 40.70 U gFW^?1 and 77.45 U gFW^?1 in low Ca treatment. A negative correlation was found between Ca concentration, level of H₂O₂, POD, PPO in tomato, and disease severity, indicating that they played an important role in resistance of tomato to this disease. These results suggested that Ca was involved in the regulation of H₂O₂ concentration, and activity of POD and PPO in tomato.     

Distribution of Pseudomonas solanacearum in the stem tissues of tomato plants with different levels of resistance to bacterial wilt

Ten tomato cultivars, from the USA, Taiwan and French Antilles, were compared for resistance to bacterial wilt as measured by disease and pathogen population invasiveness and density in the stem at the collar and midstem regions. On the basis of disease incidence, cultivars ranked from highly susceptible to totally resistant. By contrast, no significant difference was observed in bacterial population in wilting plants, regardless of the cultivar. All symptomless plants were latently infected at the collar level. Percentage of symptomless plants with bacteria at the midstem level was significantly correlated with the degree of resistance; the more resistant, the lower the stem colonization. Restriction of Pseudomonas solanacearum invasiveness in the vascular tissues of the stem is associated with resistance properties in tomato. This observation may be useful in developing improved criteria for selecting stable resistance to the disease.     

Effects of avirulent bacteriocin-producing strains of Pseudomonas solanacearum on the control of bacterial wilt of tobacco

Root systems of tobacco dipped in suspensions containing 2 × 10⁹ colony forming units (CFU)/ml of avirulent bacteriocin-producing strains (ABPS) of Pseudomonas solanacearum and assayed immediately after planting in steam-sterilized soil had 8 × 10⁶ CFU/root system of ABPS. The bacterial population declined to an average of 5·3 × 10⁵ CFU/root system after 30 days. Roots of seedlings dipped in bacterial suspensions of ABPS were more effectively protected against wilt caused by P. solanacearum than those dipped in suspensions of an avirulent nonbacteriocin-producing strain (ANBPS). Lipopolysaccharide (LPS) isolated from one ABPS (121) inhibited the attachment of bacteria on roots by 70% but had no effect on the reduction of wilt, whereas bacterial cells significantly reduced the disease severity as compared to LPS or water treatment. In steam-sterilized soil containing a 1:1 mixture (5 × 10⁵ CFU/g of oven-dried soil) of ABPS 121 or 237 and the virulent strain K-60, ABPS 121 reduced multiplication of the virulent strain in soil and in the rhizosphere of seedlings. When roots of seedlings were dipped in a suspension of 2 × 10⁹ CFU/ml of ABPS before planting, root colonization by the virulent strain added to steam-sterilized soil at 2 × 10⁶ CFU/g of oven-dried soil was significantly reduced. When roots were dipped in a suspension of ABPS and assayed 20 days after planting, 98% of the bacterial population was found in the original zone of inoculation and only 2% was detected in new growths of the root system. Plants which were grown in soil infested with ABPS 121 or K-60 had both strains present at variable populations along all sections of roots.     

Bacterial wilt resistance in tomato associated with tolerance of vascular tissues to Pseudomonas solanacearum

High populations of Pseudomonas solanacearum were detected in some, but not all stems of bacterial wilt resistant ('CRA 66', 'Hawaii 7996' and 'Caraibo') and susceptible ('Floradel') tomatoes. Latent infection, i.e. spread of P. solanacearum into xylem vessels, was confirmed in Caraibo, Hawaii 7996 and 'CRA 66' (the resistant parent of Caraibo). None of the plants within the resistant cultivars wilted and those cultivars were characterized by tolerance of the vascular tissues to high bacterial densities. In contrast, plants of cultivar Floradel showed consistent symptoms and wilted rapidly, with higher mean bacterial density than resistant cultivars. Bacterial wilt resistance was not associated with resistance to bacterial root invasion but with the capability of the plant to limit P. solanacearum colonization in the stem. The extent of bacterial colonization is proposed as a criterion to quantify tolerance, complementary to absence of external wilt symptoms used in breeding programmes for resistance.     

Resistance to bacterial wilt in tomato as discerned by spread of Pseudomonas (Burholderia) solanacearum in the stem tissues

Different criteria were compared for assessing bacterial wilt resistance in 13 tomato genotypes varying in disease susceptibility. Wilt severity and bacterial invasiveness at collar and midstem were compared in the field under cooler (March to May, 20–28°C) and warmer months (June to August, 23–29°C), which were unfavourable and favourable to wilt symptom expression, respectively. A model was proposed for determining resistance regardless of climatic conditions prevalent during field experimentation. This model was based on an estimate of bacterial invasiveness termed the colonization index. Using a qualitative imprint method we confirmed that the more resistant the genotype, the lower the bacterial colonization of the stem. The colonization index accounted both for wilted plants and for infected asymptomatic plants in which Pseudomonas solanacearum populations failed to produce wilt. The colonization index at midstem was the more useful indicator of resistance under favourable conditions. When environmental conditions were unfavourable to wilt, colonization index at collar level discerned resistant genotypes more clearly. The results formed the basis for a model for predicting the degree and stability of resistance in tomato.     

Assessment of resistance to bacterial wilt incited by Ralstonia solanacearum in tomato germplasm

Journal of Plant Diseases and Protection - Bacterial wilt incited by Ralstonia solanacearum has been found the most damaging and widespread diseases of tomato throughout the world and causes heavy...     

Nitric oxide-overproducing transformants of Pseudomonas fluorescens with enhanced biocontrol of tomato bacterial wilt

The relation between nitric oxide (NO) production and the protective ability of Pseudomonas fluorescens T5 against bacterial wilt disease in tomato was examined. The endogenous nitric oxide reductase gene of T5 was disrupted by homologous recombination using a suicide plasmid. Three disruptants were obtained, and all had higher levels of NO production. Infection with Ralstonia solanacearum was reduced in tomato plants treated with the NO-overproducing transformants compared with the wild type. These results suggest that the modification of pseudomonads to increase their level of NO production is a new approach to enhancing their biocontrol efficacy.     

番茄青枯病病原菌拮抗菌株的筛选及其田间防控作用研究

从番茄青枯病发病严重田块的健康植株根际土壤中分离筛选得到2株高效拮抗菌株,命名为W12和W118,经16SrDNA基因鉴定均属芽胞杆菌属;用PCR扩增的方法扩增脂肽类抗生素合成基因,结果表明W12和W118含有合成bacillomycin、iturin和fengycin三种抗生素的基因;将2株拮抗菌用于田间试验,结果表明混合菌株防控效果最好,3次灌菌后防控效果达到62.3%,单独施用菌株W118较单独施用W12防控效果好,3次灌菌后防控效果达到56.7%。     

Mechanisms of resistance to Ralstonia solanacearum in tomato rootstocks and integrated management of bacterial wilt using high grafting

Journal of General Plant Pathology -     

土壤施加氧化钙对西瓜枯萎病的影响及其机理初探

为探明土壤撒施石灰对西瓜枯萎病发生的影响,本试验设计5个浓度剂量的氧化钙对连作西瓜5年的土壤进行消毒处理,通过栽培感病品种并调查植株生长情况、枯萎病发病率等指标,结合土壤中尖孢镰刀菌西瓜专化型1号小种病原菌孢子量和土壤pH的变化动态,以此评估土壤施加石灰防治西瓜枯萎病的效果,并利用不同浓度的钙对尖孢镰刀菌西瓜专化型菌丝生长和产孢量的影响进行防治机理的初步研究。试验结果表明,当土壤施加氧化钙后,西瓜发病率显著降低,各处理的相对防效分别为14%、57.8%、96.3%、94.7%、94.7%。在定植10d后,各处理均有促进植株生长发育的作用,其中1.34g/kg最显著。而随着氧化钙施加量的增加,土壤pH值也不断提高,30d趋于稳定。对土壤病原菌孢子数量检测表明:各处理土壤中病原菌数量均呈现显著降低的趋势。PDA平板生测结果表明,当钙离子浓度高于80mmol/L时,病原菌的生长及产孢量开始受到抑制,随着浓度的增加,抑制作用加强。土壤施加氧化钙不仅能改善土壤的酸化,还能有效防控西瓜枯萎病,其机理可能是土壤pH值的提高改变了土壤微环境,不利于病原菌侵染;施加的钙离子抑制了病原菌菌丝的生长及孢子的萌发。研究结果对揭示氧化钙防控西瓜枯萎病机制,具有一定的参考价值。     

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。     

Effects of soil application of fly ash on the fusarial wilt on tomato cultivars

A study was carried out in microplots to evaluate the effect of fly ash on the plant growth and yield of tomato cultivars, Pusa Ruby, Pusa Early Dwarf and New Uday, and on wilt disease caused by Fusarium oxysporum f.sp. lycopersici . Fly ash was applied to soil by broadcast or in rows at the rate of 1, 2, 3 and 4 kg ash m-2 in place of inorganic fertilizers. In control plots, NPK (about 40 : 20 : 20 kg acre-1) and compost were added in place of fly ash. Ash application greatly increased the soil contents of P, K, B, Ca, Mg, Mn, Zn, carbonates, bicarbonates and sulphates. Plants grown in the ash-treated plots, especially at 3 or 4 kg dose, showed luxuriant growth and greener foliage, and plant growth and yield of the three cultivars were significantly increased in comparison with the plants grown in plots without fly ash. The wilt fungus, F. oxysporum f.sp. lycopersici at the inoculum level of 2 g plant-1 caused significant suppression of growth and yield in all three cultivars. Application of fly ash, however, checked the suppressive effect of the fungus, leading to a significant increase in the considered variables compared with the inoculated control. Soil population of the fungus (colony-forming units g soil-1) gradually decreased with an increase in ash dose. Row application was found to be relatively more effective in enhancing the yield of tomato cultivars and suppressing the wilt disease. The greatest increase in the yield of fungus inoculated and uninoculated plants due to broadcast or row application at 3 or 4 kg ash m-2 was recorded in tomato cv. Pusa Ruby (39 - 61 and 9 - 24%), followed by Pusa Early Dwarf (31 - 61 and 17 - 34%) and New Uday (21 - 35 and 4 - 22%).     

马铃薯与玉米不同套种模式对马铃薯青枯病的防治作用

田间调查比较马铃薯与玉米不同套种模式对马铃薯青枯病的控制作用结果表明,马铃薯套种玉米可减少青枯病病菌在株行间的蔓延,抑制马铃薯青枯病的发生。套种田块的青枯病发生率、大中薯减产率和单株减产量均低于纯种田块。马铃薯与玉米二套二种植模式对马铃薯青枯病的防治作用最为明显,发病率仅为纯种模式的60%左右。     

Enhanced control of bacterial wilt of tomato by DL-3-aminobutyric acid and the fluorescent Pseudomonas isolate CW2

Journal of Plant Diseases and Protection - Soil treatments with DL-3-aminobutyric acid (BABA) and the fluorescent Pseudomonas isolate CW2 significantly reduced bacterial wilt on tomato plants...     

Suppression of bacterial wilt of tomato by soil amendment with mushroom compost containing <Emphasis Type="Italic">Bacillus amyloliquefaciens</Emphasis> IUMC7

Bacillus amyloliquefaciens IUMC7 and its culture supernatant, which we previously found to suppress Fusarium wilt, were found here to have antimicrobial activity against Ralstonia solanacearum. In in vivo experiments, mushroom compost inoculated with IUMC7 significantly reduced disease severity in tomato plants over that in control soils. The R. solanacearum population decreased in soil inoculated with IUMC7. A TLC–bioautography assay showed that one of the antimicrobial substances produced by IUMC7 is likely an iturin-like lipopeptide. These results suggest that these antimicrobial compounds are responsible for disease suppression and that mushroom compost containing IUMC7 has potential as a biocontrol product.     

Effects of para-aminobenzoic acid on bacterial speck symptom development and Pseudomonas syringae pv. tomato populations in tomato leaves

Para-aminobenzoic (PABA) is reported to induce resistance against a range of plant pathogens in different crops in a salicylic acid-dependent manner. However, factors affecting its efficacy are not well understood. Foliar PABA applications on tomato seedlings reduced lesion incidence caused by Pseudomonas syringae pv. tomato (Pst) in a dose-dependent manner in distal leaves up to 18 mM under controlled environment conditions, but only three out of six commercial processing tomato cultivars tested showed a response to PABA. Leaves in direct contact with 9 and 18 mM PABA of both PABA-responsive and PABA-nonresponsive cultivars showed phytotoxicity. In a PABA-responsive cultivar, one, two and three PABA applications were equally effective at reducing lesion incidence in distal leaves, but the duration of control only persisted for approximately 7 days. Although PABA application reduced lesion incidence in distal leaves, the Pst population in leaves was unaffected. Lesions on PABA-treated plants were larger than nontreated plants, and thus the proportion of leaf surface area with lesions was unaffected by PABA treatment. In in vitro assays, 18 and 72 mM PABA produced zones of inhibition against Pst 15 and 50% larger than the ethanol control, demonstrating direct antimicrobial effects of PABA. PABA application did not affect symptom development in a mixed infection of Pst or Xanthomonas spp. in one field experiment with a PABA-responsive cultivar. Further research is needed to understand why PABA was unsuccessful in the field before it is to be used as a practical disease management tool for foliar bacterial diseases of tomato.

     

青枯菌无致病力菌株对烟草青枯病的控病作用初步研究

从茄子、番茄、辣椒、烟草青枯病株中分离出116株无致病力青枯菌,室内平板喷雾法拈抗试验结果表明,有21株菌在NA培养基上可明显抑制青枯菌TbRs的生长;烟草MSK326品种温室盆栽控病试验表明,Tnljdl-3和Aujd8—2—1两株菌具有较好控病效果,20d后的相对防效分别为58．4％和97％。     

The effect of rufianic acid on tomato wilt in relation to calcium supply

Tissue browning and wilting ofFusarium-infected tomato plants were suppressed by rufianic acid. However, calcium proved to be necessary for the action of rufianic acid as a therapeutant. An interrelationship between the effects of Ca supply and of rufianic acid on wilt disease in tomato plants and on growth was demonstrated.The amino acid contents of the exudates of decapitated plants and the Ca supply were found to be inversely related. Rufianic acid caused a decrease in the concentration of amino acids in exudates of infected as well as of healthy plants.In several respects rufianic acid kept infected plants in a near normal condition.