Growth inhibitors associated with fusarium wilt of tomato

The localization of vascular infections by a process of vascular occlusion is a primary basis for single dominant gene resistance of tomato to fusarium wilt. Failure of this response process to prevent systemic spread of fusarium in susceptible tomato plants is associated with an inhibition of tylose development, a key factor in the overall walling off process. This research was designed to detect, isolate and characterize inhibitory metabolites that accumulate during the course of the tomato/ Fusarium interaction which could inhibit tylose development. Isolation of inhibitors from chloroform extracts of systemically infected tissues was achieved by a series of successive chromatographic separations and bioassays. R_FValues of inhibitors in the several solvent systems employed and their respective colour reactions with chromogenic reagents were recorded. The accumulation of a highly inhibitory compound in chloroform extracts during the early stages of Fusarium infection was determined quantitatively by colourimetric assay in a subsequent experiment. This compound, tentatively identified as rishitin, was isolated from the region of initial infection in stem vascular tissues 1–11 days after inoculation. This inhibitor accumulated rapidly in near-isolines of both resistant and susceptible tomato cultivars in 1–4 days and then continued to accumulate in susceptible, but declined in resistant, plants from 5 to 11 days. The relative phytotoxicity of this compound at low concentrations was determined by assessing its effects on the viability of cultured tomato cells. These data, together with measurements of its accumulation and determinations of its distribution in infected tissues, indicates that rishitin, a host product that accumulates in response to infection, could account for the inhibition of tylose development observed in susceptible tomato plants following infection by Fusarium. Thus we are faced with a paradox in that a substance that presumably functions in defence can, under certain circumstances, interfere with the defence process. A likely resolution of this paradox is discussed.     

Antifungal activity of pomegranate peel extract against fusarium wilt of tomato

Pomegranate (Punica granatum) is an important source of bioactive compounds and has been used in folk medicine for many centuries. This paper describes the in vitro antifungal activity of pomegranate peel aqueous extract (pae) on the development of Fusarium wilt of tomato caused by Fusarium oxysporum, f. sp. lycopersici. HPLC-DAD-ESI/MS analysis was performed to identify punicalagins and ellagic acid, which are the main antifungal compounds. In vivo tests established the efficacy of pae treatments in controlling Fusarium wilt by evaluating improvements in growth variables of tomato plants. At high concentrations, pae showed allelopathic activity in tomato plants. The germination and the radicle growth of tomato seeds were significantly affected by pae. Increasing the extract concentration led to a progressive decrease in germination and in the length of the radicle. The reduction of the Fusarium population in soil and the increase in number of healthy plants obtained as a result of pae treatments indicate that this plant extract could have an important role in biologically-based management strategies for the control of Fusarium wilt in tomato crops.     

Cyanobacteria mediated plant growth promotion and bioprotection against Fusarium wilt in tomato

Cyanobacteria - phytopathogenic fungi - tomato plant interactions were evaluated for developing suitable biological options for combating biotic stress (Fusarium wilt) and enhancing plant vigour. Preliminary evaluation was undertaken on the fungicidal and hydrolytic enzyme activity of the cyanobacterial strains (Anabaena variabilis RPAN59, A. laxa RPAN8) under optimized environmental/nutritional conditions, followed by amendment in compost-vermiculite. Such formulations were tested against Fusarium wilt challenged tomato plants, and the Anabaena spp. (RPAN59/8) amended composts significantly reduced mortality in fungi challenged treatments, besides fungal load in soil. Cyanobacteria amended composts also led to an enhancement in soil organic C, nitrogen fixation, besides significant improvement in growth, yield, fruit quality parameters, N, P and Zn content. The tripartite interactions also enhanced the activity of defence and pathogenesis related enzymes in tomato plants. A positive correlation (r?=?0.729 to 0.828) between P content and pathogenesis/defense enzyme activity revealed their role in enhancing the resistance of the plant through improved nutrient uptake. Light and scanning electron microscopy (SEM) revealed cyanobacterial colonization, which positively correlated with reduced fungal populations. The reduced disease severity coupled with improved plant growth/ yields, elicited by cyanobacterial treatments, illustrated the utility of such novel formulations in integrated pest and nutrient management strategies for Fusarium wilt challenged tomato crop.     

Foliar spray of validamycin a or validoxylamine a controls tomato fusarium wilt

ABSTRACT Tomato wilt, caused by the soilborne fungus Fusarium oxysporum f. sp. lycopersici, is effectively controlled by a foliar spray of validamycin A (VMA) or validoxylamine A (VAA) (>/=10 mug/ml); however, neither VMA nor VAA is antifungal in vitro. In pot tests, the effect of a foliar application of VMA or VAA at 100 mug/ml lasted for 64 days. Plants sprayed with VMA or VAA accumulated salicylic acid and had elevated expression of the systemic acquired resistance (SAR) marker genes P4 (PR-1), Tag (PR-2), and NP24 (PR-5). Foliar spray of VMA also controlled late blight and powdery mildew of tomato. The disease control by VMA and VAA lasted up to 64 days after treatment, was broad spectrum, and induced the expression of PR genes, all essential indicators of SAR, suggesting that VMA and VAA are plant activators. The foliar application of plant activators is a novel control method for soilborne diseases and may provide an economically feasible alternative to soil fumigants such as methyl bromide.     

Repeated applications of Penicillium oxalicum prolongs biocontrol of fusarium wilt of tomato plants

The suppression of fusarium wilt of tomato achieved by Penicillium oxalicum (PO) applied one or several times (up to four) was assessed during three glasshouse experiments. The first application of PO (10⁶ conidia g^-1 substrate) to the growing substrate (peat and vermiculite, 1 : 1, v : v) was performed prior to its infestation with Fusarium oxysporum f. sp. lycopersici (FOL) (10⁴–10⁶ chlamydospores g^-1). Repeated applications of PO prolonged the duration of control of fusarium wilt especially when disease incidence was high. The timing of repeated applications of PO did not affect the efficacy of the control. Disease reduction was not associated with a decrease in density of FOL in the rhizosphere, irrespective of the number of applications of PO. Density of PO in the tomato rhizosphere was higher when repeated applications were made. No relationship was observed between reduction of disease and high densities of PO. Reasons for a longer disease reduction in tomato plants following several applications with PO are discussed.     

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.     

An electron microscope study of tomato spotted wilt virus in the plant cell

Characteristic particles of about 70 m diameter were found in tomato spotted wilt virus (TSWV) infected cells of roots, stems, leaves and petals of several plant species. These particles were similar in size and form to those found in the pellets of partially purified infective TSWV.     

Paclobutrazol and other plant growth-retarding chemicals increase resistance of melon seedlings to fusarium wilt

Studies were made of plant growth retardation and effects on resistance of melon to fusarium wilt by soil application of paclobutrazol, other ergosterol biosynthesis inhibitors, the fungicide benomyl and the herbicide dinitramine. Paclobutrazol and ancymidol delayed the onset of wilting and were the most effective in reducing wilt incidence. A relationship between effectiveness in retarding seedling elongation and increasing resistance to fusarium wilt was observed. No chemical had a significant effect on pathogen population level in the plant, as determined by stem colonization and direct assessment tests in seedlings grown in soil treated with the chemicals. Excluding benomyl, and to a lesser extent dinitramine, leaf and stem extracts had no inhibitory effect on conidial germination. Gibberellins GA₄₊₇, when applied to seedlings inoculated after germination in paclobutrazol-treated soil, nullified growth retardation and increased disease incidence. We suggest that disease incidence reduction by paclobutrazol is due to an effect on plant metabolic processes and not to direct fungitoxicity of the compound.     

Influence of temperature on plant–rhizobacteria interactions related to biocontrol potential for suppression of fusarium wilt of chickpea

Seed and soil treatment with Pseudomonas fluorescens RGAF 19, P. fluorescens RG 26, Bacillus megaterium RGAF 51 and Paenibacillus macerans RGAF 101 can suppress fusarium wilt of chickpea ( Cicer arietinum ), but the extent of disease suppression by these rhizobacteria is modulated by soil temperature. In this work, the effect of temperature on plant–rhizobacteria interactions was assessed in relation to biocontrol potential for suppression of fusarium wilt of chickpea. Seed and soil treatment with those rhizobacteria delayed seedling emergence compared with nontreated controls, and either increased or had no deleterious effect on chickpea growth. Pseudomonas fluorescens isolates significantly increased chickpea shoot dry weight at 20°C and root dry weight at 25 and 30°C. All bacterial isolates colonized the chickpea rhizosphere and internal stem tissues at 20, 25 and 30°C, and there was a positive linear trend between bacterial population size in the rhizosphere and temperature increase. The maximum inhibition of mycelial growth and conidial germination of Fusarium oxysporum f. sp. ciceris race 5 in vitro occurred at a temperature range optimal for bacterial growth and production of inhibitory metabolites. These results demonstrate the need to understand the effects of environmental factors on the biological activities of introduced rhizobacteria of significant importance for plant disease suppression.     

Effect of plant age at time of infection by tomato spotted wilt tospovirus on the yield of field-grown tomato

Naturally infected tomato plants that expressed tomato spotted wilt virus symptoms at 24, 38, 45, 60, 67, and 74 days after transplanting were monitored for production in an experimental crop grown in the open from May to September in northeastern Spain. Plants were tagged, tested for tomato spotted wilt virus infection by enzyme-linked immunosorbent assay, and data on symptom expression and yield were individually recorded. Plants that developed symptoms at 24, 38, or 45 days after transplanting yielded significantly less and produced fewer and smaller tomatoes than those that developed symptoms at 60, 67, and 74 days after transplanting. These later infected plants showed similar patterns of production with maximum yields between 27 July and 17 August, when most fruit was harvested. Production components such as fruit number per plant, yield of mature fruit per plant, or fruit weight increased the older the plants were when first symptoms were exhibited. However, marketable fruit production was drastically decreased by tomato spotted wilt virus infection, due to abnormal ripening of mature fruit in infected plants. Little and no significantly different amounts of marketable fruit were produced, irrespectively of plant age at time of symptom expression. Implications for spotted wilt management in tomato are discussed.     

A molecular diagnostic for tropical race 4 of the banana fusarium wilt pathogen

This study analysed genomic variation of the translation elongation factor 1α (TEF‐1α) and the intergenic spacer region (IGS) of the nuclear ribosomal operon of Fusarium oxysporum f. sp. cubense (Foc) isolates, from different banana production areas, representing strains within the known races, comprising 20 vegetative compatibility groups (VCG). Based on two single nucleotide polymorphisms present in the IGS region, a PCR‐based diagnostic tool was developed to specifically detect isolates from VCG 01213, also called tropical race 4 (TR4), which is currently a major concern in global banana production. Validation involved TR4 isolates, as well as Foc isolates from 19 other VCGs, other fungal plant pathogens and DNA samples from infected tissues of the Cavendish banana cultivar Grand Naine (AAA). Subsequently, a multiplex PCR was developed for fungal or plant samples that also discriminated Musa acuminata and M. balbisiana genotypes. It was concluded that this diagnostic procedure is currently the best option for the rapid and reliable detection and monitoring of TR4 to support eradication and quarantine strategies.     

甘薯主栽品种对甘薯瘟和蔓割病抗性评价

用甘薯瘟 2个致病型菌株对我国南方薯区 16份主栽品种分菌系接种鉴定 ,结果表明新种花、胜利百号等 10份表现为高感～感病。瑞薯 1号等 3份为高抗Ⅰ型菌、感Ⅱ型菌 ;徐薯 18则为中抗Ⅱ型菌、感Ⅰ型菌。广薯 88-70和湘薯75-55显示出高抗Ⅰ型菌兼具中抗Ⅱ型菌。用蔓割病菌对 16份主栽品种接种鉴定结果表明 ,广薯 111、潮薯 1号等 7份表现高感～中感 ;而福薯26、岩薯5号等9份则为中抗～高抗     

Biological control of fusarium wilt of cucumber by chitinolytic bacteria

ABSTRACT Two chitinolytic bacterial strains, Paenibacillus sp. 300 and Streptomyces sp. 385, suppressed Fusarium wilt of cucumber (Cucumis sativus) caused by Fusarium oxysporum f. sp. cucumerinum in nonsterile, soilless potting medium. A mixture of the two strains in a ratio of 1:1 or 4:1 gave significantly (P < 0.05) better control of the disease than each of the strains used individually or than mixtures in other ratios. Several formulations were tested, and a zeolite-based, chitosan-amended formulation (ZAC) provided the best protection against the disease. Dose-response studies indicated that the threshold dose of 6 g of formulation per kilogram of potting medium was required for significant (P < 0.001) suppression of the disease. This dose was optimum for maintaining high rhizosphere population densities of chitinolytic bacteria (log 8.1 to log 9.3 CFU/g dry weight of potting medium), which were required for the control of Fusarium wilt. The ZAC formulation was suppressive when added to pathogen-infested medium 15 days before planting cucumber seeds. The formulation also provided good control when stored for 6 months at room temperature or at 4 degrees C. Chitinase and beta-1,3-glucanase enzymes were produced when the strains were grown in the presence of colloidal chitin as the sole carbon source. Partial purification of the chitinases, followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and activity staining, revealed the presence of five bands with molecular masses of 65, 62, 59, 55, and 52 kDa in the case of Paenibacillus sp. 300; and three bands with molecular masses of 52, 38, and 33 kDa in the case of Streptomyces sp. 385. Incubation of cell walls of F. oxysporum f. sp. cucumerinum with partially purified enzyme fractions led to the release of N-acetyl-D-glucosamine (NAGA). NAGA content was considerably greater when pooled enzyme fractions (64 to 67) from Paenibacillus sp. were used, because they contained high beta-1,3-glucanase activity in addition to chitinase activity. Suppression of Fusarium wilt of cucumber by a combination of these two bacteria may involve the action of these hydrolytic enzymes.     

蛇床子提取物对黄瓜枯萎病菌抑制效果的研究

从蛇床子中提取抑制黄瓜枯萎菌的活性成分,正交优选提取条件,并在不同浓度下测定其抑制效果。结果表明,在室温下,95%乙醇连续超声提取3次,每次45 min为宜;当提取物浓度为10 mg/mL时,菌丝生长抑制率达78.65%;浓度大于100 mg/L时,孢子萌发抑制率为100%;浓度为8 mg/mL时,相对防效为40.95%。     

Yield loss in chickpeas in relation to development of fusarium wilt epidemics

ABSTRACT Development of 108 epidemics of Fusarium wilt of chickpea caused by Fusarium oxysporum f. sp. ciceris were studied on cvs. P-2245 and PV-61 in field microplots artificially infested with races 0 and 5 of F. oxysporum f. sp. ciceris in 1986 to 1989. Disease progression data were fitted to the Richards model using nonlinear regression. The shape parameter was influenced primarily by date of sowing and, to a lesser extent, by chick-pea cultivars and races of F. oxysporum f. sp. ciceris. Fusarium wilt reduced chickpea yield by decreasing both seed yield and seed weight. These effects were related to sowing date, chickpea cultivar, and virulence of the prevalent F. oxysporum f. sp. ciceris race. Regression models were developed to relate chickpea yield to Fusarium wilt disease intensity with the following independent variables: time to initial symptoms (t(is)), time to inflection point (t(ip)) of the disease intensity index (DII) progress curve, final DII (DII(final)), standardized area under DII progress curve (SAUDPC), and the Richards weighted mean absolute rate of disease progression (rho). Irrespective of the chickpea cultivar x pathogen race combination, the absolute and relative seed yields decreased primarily by delayed sowing. The relative seed yield increased with the delay in t(is) and t(ip) and decreased with increasing DII(final), SAUDPC, and rho. A response surface as developed in which seed yield loss decreased in a linear relationship with the delay in t(is) and increased exponentially with the increase of rho.     

Benomyl-resistant Fusarium-isolates in ecological studies on the biological control of fusarium wilt in carnation

Ecological properties and stability of benomyl resistance of three benomyl-resistant mutants of nonpathogenicFusarium-isolates antagonistic to fusarium wilt in carnation, and three benomyl-resistant mutants of a pathogenic isolate ofFusarium oxysporum f.sp.dianthi were evaluatedin vitro and in glasshouse experiments. The benomyl resistance of the nonpathogenic mutants was stable under all conditions tested, also after a 1000-fold increase of the population in sterilized soil. Mutants of the pathogen were stable during allin vitro tests, but after proliferation in carnation stems only part of the population was benomyl resistant.Compared to the wild type, mutants of the pathogen were less pathogenic, also if thein vitro propeties were similar. Colonization of carnation by benomyl-resistant nonpathogenicFusarium in the presence of the pathogen showed that the antagonistic effect correlated with the presence of the nonpathogenic isolates within the carnation stem. The wild types and two of the mutant nonpathogenicFusarium-isolates controlled fusarium wilt in the susceptible cultivar Lena for 50% or more.UV-induced benomyl resistance appeared to be a valuable marker to distinguish between differentFusarium isolates and to study the population dynamics, but intensive screening of the mutants is a prerequisite since alterations in antagonism and pathogenicity can occur.     

Soil solarization for the control of verticillium wilt of greenhouse tomato

Verticillium dahliae, the causal agent of Verticillium wilt of tomato, causes serious damage to crops grown in unheated greenhouses. To control this disease, growers are obliged to employ strong soil disinfestants. The possibility of controllingV. dahliae by using soil solarization during the months of June — August was examined. The soil was covered with transparent polyethylene sheets for 10 weeks. The pathogen could not be isolated from the solarized soil, whereas the inoculum level in the nonsolarized soil remained high (1379–1806 propagules/g soil). The yield from the solarized soil was increased by 112.4% in comparison with the control, and no infected plants were observed. The percentage of infected roots was very low (0.3–0.4%) in relation to the nonsolarized soil (66.7–67.1%). From these results it was concluded that solarization can effectively control Verticillium wilt of greenhouse-grown tomato under the summer conditions in Crete.     

Resistance-breaking tomato spotted wilt orthotospovirus isolates on resistant tomato in Serbia

Journal of Plant Diseases and Protection - The most effective management strategy for tomato spotted wilt orthotospovirus (TSWV) has been the use of resistant tomato (Sw-5b+) cultivars....     

香蕉枯萎病菌的培养性状和致病性研究

2001～2004年对采自海南省各市县香蕉种植区发病的1 8个香蕉和粉蕉假茎枯萎病菌分离物进行了培养性状及致病性研究。结果表明,海南省香蕉和粉蕉假茎枯萎病菌的分离物不仅在培养特性上存在明显区别,且在致病性上也存在强、弱2种不同类型:即致病性极强的4号生理小种和致病性相对较弱的1号生理小种。