Cucumber Fusarium Wilt Research Articles

The influence of different concentrations of bio-organic fertilizer on cucumber Fusarium wilt and soil microflora alterations

Fusarium wilt is one of the main diseases of cucumber, and bio-organic fertilizer has been used to control Fusarium wilt. In this study, a pot experiment was conducted to evaluate the effects of bio-organic fertilizer applied at four levels on the suppression of Fusarium wilt disease in cucumber, the soil physico-chemical properties and the microbial communities. In comparison with the control (CK), low concentrations of bio-organic fertilizer (BIO2.5 and BIO5) did not effectively reduce the disease incidence and had little effect on soil microorganisms. High concentrations of bio-organic fertilizer (BIO10 and BIO20) significantly reduced the disease incidence by 33.3%-66.7% and the production was significantly improved by 83.8%-100.3%. The soil population of F. oxysporum f. sp. cucumerinum was significantly lower in bio-organic fertilizer treatments, especially in BIO10 and BIO20. The microorganism activity increased with the bio-organic fertilizer concentration. High-throughput sequencing demonstrated that, at the order level, Sphingomonadales, Bacillales, Solibacterales and Xylariales were significantly abundant in BIO10 and BIO20 soils. At the genus level, the abundance and composition of bacterial and fungal communities in BIO10 and BIO20 were similar, illustrating that high concentrations of bio-organic fertilizer activated diverse groups of microorganisms. Redundancy analysis (RDA) showed that Xanthomonadales, Sphingomonadales, Bacillales, Orbiliales, Sordariales, and Mucorales occurred predominantly in the BIO10 and BIO20. These microorganisms were related to the organic matter, available potassium and available phosphorus contents. In conclusion, a high concentration of bio-organic fertilizer application suppressed the Fusarium wilt disease and increased cucumber production after continuous cropping might through improving soil chemical condition and manipulating the composition of soil microbial community.

Varietal Reaction of Cucumber (Cucumis sativus L.) Germplasm for Management of Fusarium Wilt of Cucumber (FWC)

Twelve cucumber varieties/lines (Cuc-30, Cuc-05, Local, Rocky, Hcu-163A, Hashim, Guard HC1, Qasim, Durga, Shaheen, Happy and Green cucumber) were cultivated to find out their genetic potential against Fusarium wilt disease of cucumber in research area of the Department of Plant Pathology University of Agriculture Faisalabad under randomized complete block design (RCBD). None of them was immune and resistant against fusarium wilt of cucumber. Among twelve varieties nine varieties (Green cucumber, Hashim, Rocky, Cu-05, Happy, Durga, Guard HC-1, Cu-30 and Qasim) exhibited moderately susceptible response with 38.0%, 37.78%, 36.0%, 34.0%, 31.12%, 28.0%, 26.0%, 26.0% and 44.45% disease incidence respectively. Shaheen (20.0%) and Hcu-163A (22.50%) expressed moderately resistant response while only one variety (Local) gave highly susceptible reaction with a disease incidence of 55.0%.

Decrease in the Incidence of Cucumber Fusarium Wilt in Varamin Greenhouses using Talaromyces Flavus

Decrease in the Incidence of Cucumber Fusarium Wilt in Varamin Greenhouses using Talaromyces Flavus

Comparative proteomic analysis of cucumber roots infected by Fusarium oxysporum f. sp. cucumerium Owen

Cucumber Fusarium wilt (CFW), caused by the soil-borne fungus Fusarium oxysporum f. sp. cucumerium, is a serious disease in cucumber (Cucumis sativus) production worldwide. For the efficient control of the pathogenic fungi, a better understanding of its interaction and associated resistance mechanisms at the molecular level is required. Here, we report a comparative proteomics analysis of total root protein isolated from infected cucumber root of susceptible bulk (SB) and resistant bulk (RB) of cucumber generation F2. Two-dimensional gel electrophoresis (2-DE) coupled with MS/MS approaches identified 15 over-accumulated proteins from the RB plants. Identified proteins are mainly involved in defense and stress responses, oxidation reduction, metabolism and transport and other process. These proteins are likely to be a part of resistance-related protein network, playing different roles in cucumber disease resistance. Three vital clues regarding wilt resistance of C. sativus are gained from this study. First, jasmonic acid and redox signaling components were found in response to F. oxysporum infection in resistant plants. Second, the LRR family protein may play an important role in the defense reaction against CFW. Third, biotic and abiotic stress-related proteins were induced by the CFW fungus F. oxysporum, indicating the activation of common stress pathway.

Vinegar residue compost as a growth substrate enhances cucumber resistance against the Fusarium wilt pathogen Fusarium oxysporum by regulating physiological and biochemical responses.

Fusarium wilt caused by the fungus Fusarium oxysporum f. sp. cucumerinum (FOC) is the most severe soil-borne disease attacking cucumber. To assess the positive effects of vinegar residue substrate (VRS) on the growth and incidence of Fusarium wilt on cucumber, we determined the cucumber growth parameters, disease severity, defense-related enzyme and pathogenesis-related (PR) protein activities, and stress-related gene expression levels. In in vitro and pot experiments, we demonstrated the following results: (i) the VRS extract exhibited a higher biocontrol activity than that of peat against FOC, and significantly improved the growth inhibition of FOC, with values of 48.3%; (ii) in response to a FOC challenge, antioxidant enzymes and the key enzymes of phenylpropanoid metabolic activities, as well as the PR protein activities in the roots of cucumber, were significantly increased. Moreover, the activities of these proteins were higher in VRS than in peat; (iii) the expression levels of stress-related genes (including glu, pal, and ethylene receptor) elicited responses to the pathogens inoculated in cucumber leaves; and (iv) the FOC treatment significantly inhibited the growth of cucumber seedlings. Moreover, all of the growth indices of plants grown in VRS were significantly higher than those grown in peat. These results offer a new strategy to control cucumber Fusarium wilt, by upregulating the activity levels of defense-related enzymes and PR proteins and adjusting gene expression levels. They also provide a theoretical basis for VRS applications.

Isolation and identification of biocontrol agent Streptomyces rimosus M527 against Fusarium oxysporum f. sp. cucumerinum.

Actinomycetes have received considerable attention as biocontrol agents against fungal plant pathogens and as plant growth promoters. In this study, a total of 320 actinomycetes were isolated from various habitats in China. Among which, 77 strains have been identified as antagonistic activities against Fusarium oxysporum f. sp. cucumerinum which usually caused fusarium wilt of cucumber. Of these, isolate actinomycete M527 not only displayed broad-spectrum antifungal activity but also showed the strongest antagonistic activity against the spore germination of F. oxysporum f. sp. cucumerinum. In pot experiments, the results indicated that isolate M527 could promote the shoot growth and prevent the development of the disease on cucumber caused by F. oxysporum f. sp. cucumerinum. The control efficacy against seedling fusarium wilt of cucumber after M527 fermentation broth root-irrigation was up to 72.1% as compared to control. Based on 16S rDNA sequence analysis, the isolate M527 was identified as Streptomyces rimosus.

Biological characteristics of Streptomyces albospinus CT205 and its biocontrol potential against cucumber Fusarium wilt

ABSTRACTIn a dual-culture assay, Streptomyces albospinus CT205 inhibited the growth of Fusarium oxysporum in vitro, the casual agent of widespread Fusarium wilt, probably due to the production of chitinase, β-glucanase, and a heat-resistant antagonistic substance. Pot and field experiments were performed to investigate the effects of S. albospinus CT205 alone or combined with organic fertiliser (BOF-CT205) on control of Fusarium wilt. Pot experiments showed that BOF-CT205 treatments obtained the lowest disease index (23.2), compared with organic fertiliser (OF, 55.3), strain CT205 (66.2), and control (72.5) treatments. In the field experiment, BOF-CT205 treatment yielded significantly lower disease incidences than the control, with reductions of ca. 55%. Cucumber yields in the same treatments were significantly higher than in the control, with increases of approximately 30% in the OF treatment. The cucumber yield was maximised in the BOF-CT205 in field experiments, reaching 8.3 × 104 kg ha−1. The application of BOF-CT205 reduced the presence of the pathogen in the cucumber rhizosphere. In conclusion, S. albospinus CT205 was demonstrated to be a promising biocontrol agent for cucumber wilt, and the most effective treatment was the application of BOF-CT205.

Novel soil fumigation method for suppressing cucumber Fusarium wilt disease associated with soil microflora alterations

Fusarium wilt in cucumber results from continuous cropping and is a serious soil-borne fungal disease that threatens cucumber production around the world. The application of a novel fumigation agent based on ammonium bicarbonate to the soil as a strategy for controlling Fusarium wilt and its effects on soil microflora was investigated in a field with serious disease incidence in this study. Overall, the results showed that fumigation effectively controlled cucumber Fusarium wilt disease and significantly increased the total and mean cucumber fruit weight. Real-Time PCR results showed that the total bacterial and fungal numbers in the treatment (LAB) significantly decreased after fumigation and that significantly fewer fungi were observed after harvest (LABOF). The next-generation sequencing of the 16S rRNA and internal transcribed spacer (ITS) genes using MiSeq platform showed that the soil bacterial and fungal community structures in the fumigation treatment were significantly different from the control without fumigation regardless after fumigation or harvest. Compared to the control, higher abundances of Gemmatimonadetes, Verrucomicrobia and Zygomycota, and lower abundance of Ascomycota were observed in the fumigated soils after fumigation and harvest. Furthermore, the abundances of Mortierella and Gp1 were significantly higher. Most importantly, the abundance of Fusarium, which includes the pathogen potentially responsible for cucumber Fusarium wilt disease, was significantly lower in the fumigated soils after harvest. Redundancy analysis showed that the fumigated soils were dominated by Ohtaekwangia, Gp6, and Gp4, which were related to the soil total nitrogen (TN), ammonium nitrogen (NH4–N) and nitrate nitrogen (NO3–N) contents. In addition, Penicillium and Pseudaleuria fungi were dominant in the treatment and control, and the control was dominated by Fusarium. In conclusion, the observed disease suppression due to the novel ecological soil fumigation strategy may be attributed to general suppression resulting from altered soil properties, such as higher soil NH4–N, NO3–N and TON contents, and the alteration of the disturbed soil microflora in a cucumber monoculture system.

Effect of vinegar residue compost amendments on cucumber growth and Fusarium wilt.

Fusarium wilt of cucumber caused by Fusarium oxysporum f. sp. cucumerinum J. H. Owen is one of the major destructive soilborne diseases and results in considerable yield losses. Methyl bromide was once the most effective disease control method but has been confirmed as harmful to the environment. Using suppressive media as biological controls to assist crop growth is becoming popular. In this study, Fusarium wilt of cucumber was successfully controlled by a newly identified suppressive media: vinegar residue compost-amended media (vinegar residue compost mixed with peat and vermiculite in a 6:3:1 ratio (v/v) vinegar residue substrate (VRS). Greenhouse experiments were carried out to evaluate the effect of VRS on the growth of cucumber seedlings and disease suppression. The control was peat/vermiculite (2:1, v/v). To identify the mixed media most suitable for the growth of plants and their suppressiveness indicators, we evaluated the biological characteristics of cucumber, the physicochemical and biochemical properties of the growth media, and the enzyme activities. Total organic C (C(org)), microbial biomass C (C(mic)), basal respiration (R(mic)), and enzyme (catalase, invertase, urease, proteinase, phosphatase, β-glucosidase, and hydrolysis of fluorescein diacetate) activities increased significantly after vinegar waste compost amendment. The compost media also showed a significantly positive effect on the growth of cucumber seedlings and the suppression of the disease severity index (DSI, 38% reduction). The cucumber rhizosphere population of F. oxysporum f. sp. cucumerinum (FOC) was significantly lower in VRS than in the control. These results demonstrate convincingly that vinegar residue compost-amended media has a beneficial effect on cucumber growth and could be applied as a method for biological control of cucumber Fusarium wilt.

In Vitro and in Vivo Management of Fusarium Wilt of Cucumber (FWC) Through Various Chemicals

Various fungicidal chemicals were evaluated against the fusarium wilt of cucumber disease. Firstly chemicals were evaluated under lab conditions and the best resulted fungicides were applied in field conditions and significant disease incidence reduction had been recorded as compared to control. Five chemicals namely redomil, score, copper oxychloride, cabriotop, antracol and a control were applied in lab conditions in three concentrations 1%, 0.5% and 0.25% following randomized complete block design (RCBD). Maximum growth inhibition of fungus mycelia was expressed by redomil (1.53cm) followed by score (1.66cm), copper oxychloride (1.75cm), cabriotop (1.79cm), and antracol (1.90cm) as compared to control (3.49cm). Hence redomil (1.53cm) and score (1.66cm) gave maximum inhibition under lab conditions these were applied to highly susceptible Local variety in same concentrations and same design cultivated in Research Area of the Department of Plant Pathology University of Agriculture Faisalabad. Redomil (47.50%) expressed minimum disease incidence and score (49.72%) as compared to control in field (55.0%).

Rhizosphere Inhibition of Cucumber Fusarium Wilt by Different Surfactin- excreting Strains of Bacillus subtilis.

Bacillus subtilis B006 strain effectively suppresses the cucumber fusarium wilt caused by Fusarium oxysporum f. sp. cucumerinum (Foc). The population dynamics of Foc, strain B006 and its surfactin over-producing mutant B841 and surfactin-deficient mutant B1020, in the rhizosphere were determined under greenhouse conditions to elucidate the importance of the lipopeptides excreted by these strains in suppressing Foc. Results showed that B. subtilis strain B006 effectively suppressed the disease in natural soil by 42.9%, five weeks after transplanting, whereas B841 and B1020 suppressed the disease by only 22.6% and 7.1%, respectively. Quantitative PCR assays showed that effective colonization of strain B006 in the rhizosphere suppressed Foc propagation by more than 10 times both in nursery substrate and in field-infected soil. Reduction of Foc population at the cucumber stems in a range of 0.96 log10 ng/g to 2.39 log10 ng/g was attained at the third and the fifth weeks of B006 treatment in nursery substrate. In field-infected soil, all three treatments with B. subtilis suppressed Foc infection, indicated by the reduction of Foc population at a range of 2.91 log10 ng/g to 3.36 log10 ng/g at the stem base, one week after transplanting. This study reveals that the suppression of fusarium wilt disease is affected by the effective colonization of the surfactin-producing B. subtilis strain in the rhizosphere. These results improved our understanding of the biocontrol mechanism of the B. subtilis strain B006 in the natural soil and facilitate its application as biocontrol agent in the field.

FocVel1 influences asexual production, filamentous growth, biofilm formation, and virulence in Fusarium oxysporum f. sp. cucumerinum.

Velvet genes play critical roles in the regulation of diverse cellular processes. In current study, we identified the gene FocVel1, a homolog of Fusarium graminearum VelA, in the plant pathogenic fungus F. oxysporum f. sp. cucumerinum. This pathogen causes the destructive disease called cucumber Fusarium wilt (CFW), which severely affects the production and marketing of this vegetable worldwide. Transcript analyses revealed high expression of FocVel1 during conidiophore development. Disruption of the FocVel1 gene led to several phenotypic defects, including reduction in aerial hyphal formation and conidial production. The deletion mutant ΔFocVel1 showed increased resistance to both osmotic stress and cell wall-damaging agents, but increased sensitivity to iprodione and prochloraz fungicides, which may be related to changes in cell wall components. In the process of biofilm formation in vitro, the mutant strain ΔFocVel1 displayed not only a reduction in spore aggregation but also a delay in conidial germination on the polystyrene surface, which may result in defects in biofilm formation. Moreover, pathogenicity assays showed that the mutant ΔFocVel1 exhibited impaired virulence in cucumber seedlings. And the genetic complementation of the mutant with the wild-type FocVel1 gene restored all the defects of the ΔFocVel1. Taken together, the results of this study indicated that FocVel1 played a critical role in the regulation of various cellular processes and pathogenicity in F. oxysporum f. sp. cucumerinum.

Erratum to: Contribution of indole-3-acetic acid in the plant growth promotion by the rhizospheric strain Bacillus amyloliquefaciens SQR9

Bacillus amyloliquefaciens SQR9, isolated from the rhizosphere of cucumber, can control Fusarium wilt of cucumber and directly stimulate plant growth. To evaluate its potential agricultural use, the plant growth promotion of B. amyloliquefaciens SQR9 was evaluated, and the relative mechanisms, especially the production of the phytohormone indole-3-acetic acid (IAA), were investigated. The related plant-growth-promoting factors were genetically and chemically analyzed, and a mutant library was constructed for selecting strains with different IAA production. B. amyloliquefaciens SQR9 showed a growth-promoting activity in greenhouse experiments. Plant-growth-promoting factors like extracellular phytase, volatile components including acetoin, 2,3-butanediol, and phytohormone IAA were detected in B. amyloliquefaciens SQR9 cultures grown under laboratory conditions. Three IAA production mutant strains showed variation in plant-growth-promoting effect. IAA production in B. amyloliquefaciens SQR9 was related to its plant-growth-promoting effect, but IAA alone could not account for the overall observed plant-growth-promoting effect. The promoted plant growth by the rhizospheric strain B. amyloliquefaciens SQR9 can be attributed to multiple factors, including production of phytohormones, volatile compounds, and extracellular enzymes. Therefore, the strain B. amyloliquefaciens SQR9 may be used as a plant-growth-promoting agent to increase crop yield.

Synergistic Effect of Dazomet Soil Fumigation and Clonostachys rosea Against Cucumber Fusarium Wilt.

Soil fumigation and biological control are two control measures frequently used against soilborne diseases. In this study, the chemical fumigant dazomet was applied in combination with the biocontrol agent (BCA) Clonostachys rosea 67-1 to combat cucumber wilt caused by Fusarium oxysporum f. sp. cucumerinum KW2-1. When the mycoparasite C. rosea 67-1 was applied after dazomet fumigation, disease control reached 100%, compared with 88.1 and 69.8% for dazomet and 67-1 agent, respectively, applied alone, indicating a synergistic effect of dazomet and C. rosea in combating cucumber Fusarium wilt based on analysis of Bliss Independence. To understand the synergistic mechanism, the effects of chemical fumigation on the colonization potential and activity of F. oxysporum f. sp. cucumerinum, and the interaction between the BCA and the pathogen were investigated. The results showed that growth of the pathogen decreased with increasing dazomet concentration subsequent to fumigation. When exposed to dazomet at 100 ppm, the fungal sporulation rate decreased by 94.4%. Severe damage was observed in fumigated isolates using scanning electron microscopy. In the greenhouse, disease incidence of cucumber caused by fumigated F. oxysporum f. sp. cucumerinum significantly decreased. Whereas germination of C. rosea 67-1 spores increased by >sixfold in fumigated soil, and its ability to parasitize fumigated F. oxysporum f. sp. cucumerinum significantly increased (P = 0.014).

Correction: Modified Primers for the Identification of Nonpathogenic Fusarium oxysporum Isolates That Have Biological Control Potential against Fusarium Wilt of Cucumber in Taiwan

Correction: Modified Primers for the Identification of Nonpathogenic Fusarium oxysporum Isolates That Have Biological Control Potential against Fusarium Wilt of Cucumber in Taiwan

Modified primers for the identification of nonpathogenic Fusarium oxysporum isolates that have biological control potential against Fusarium wilt of cucumber in Taiwan.

Previous investigations demonstrated that Fusarium oxysporum (Fo), which is not pathogenic to cucumbers, could serve as a biological control agent for managing Fusarium wilt of cucumber caused by Fo f. sp. cucumerinum (Foc) in Taiwan. However, thus far it has not been possible to separate the populations of pathogenic Fo from the nonpathogenic isolates that have biological control potential through their morphological characteristics. Although these two populations can be distinguished from one another using a bioassay, the work is laborious and time-consuming. In this study, a fragment of the intergenic spacer (IGS) region of ribosomal DNA from an Fo biological control agent, Fo366, was PCR-amplified with published general primers, FIGS11/FIGS12 and sequenced. A new primer, NPIGS-R, which was designed based on the IGS sequence, was paired with the FIGS11 primer. These primers were then evaluated for their specificity to amplify DNA from nonpathogenic Fo isolates that have biological control potential. The results showed that the modified primer pair, FIGS11/NPIGS-R, amplified a 500-bp DNA fragment from five of seven nonpathogenic Fo isolates. These five Fo isolates delayed symptom development of cucumber Fusarium wilt in greenhouse bioassay tests. Seventy-seven Fo isolates were obtained from the soil and plant tissues and then subjected to amplification using the modified primer pair; six samples showed positive amplification. These six isolates did not cause symptoms on cucumber seedlings when grown in peat moss infested with the isolates and delayed disease development when the same plants were subsequently inoculated with a virulent isolate of Foc. Therefore, the modified primer pair may prove useful for the identification of Fo isolates that are nonpathogenic to cucumber which can potentially act as biocontrol agents for Fusarium wilt of cucumber.

Efficacy of sludge and manure compost amendments against Fusarium wilt of cucumber

Fusarium wilt of cucumber caused by the fungus, Fusarium oxysporum, is one of the most destructive soilborne diseases and can result in serious economic loss. No efficient fungicide is currently available to control the disease. The aim of this study was to examine the disease suppression ability of pig manure and sludge composts in peat-based container media and explore the possible disease suppression mechanisms. Pig manure and sewage sludge compost were made in laboratory-scale tanks. Plant growth media were formulated with peat mixture and compost (or 60°C heated compost) in a 4:1 ratio (v/v). Cucumber seedlings were artificially inoculated with F. oxysporum conidia (5 × 10(5) conidia mL(-1)) by the root-dip method. Cucumber Fusarium wilt was effectively suppressed in sludge compost-amended media, while the disease suppression effect of pig manure compost was limited. The ammonia levels in the manure compost-amended media were significantly higher than those of sludge compost-amended media, which could explain its lower disease suppression ability. Heated composts behaved similarly with respect to disease suppression. Adding composts increased microbial biomass, microbial activity, and the microbial diversity of the growth media. PCR-DGGE results indicated that the fungal community had a significant correlation to the disease severity. The artificially inoculated pathogen was retrieved in all treatments and one possible biocontrol agent was identified as a strain of F. oxysporum by phylogenetic analyses. The results indicated that the sludge compost used in this study could be applied as a method for biocontrol of cucumber Fusarium wilt.

Suppression of Fusarium oxysporum and induced resistance of plants involved in the biocontrol of Cucumber Fusarium Wilt by Streptomyces bikiniensis HD-087

Cucumber Fusarium Wilt, caused by Fusarium oxysporum f. sp. cucumerinum, which usually leads to severe economic damage, is a common destructive disease worldwide. To date, no effective method has yet been found to counteract this disease. A fungal isolate, designated HD-087, which was identified as Streptomyces bikiniensis using physiological-biochemical identification and 16S rRNA sequence analysis, is shown to possess distinctive inhibitory activity against F. oxysporum. The fermentation broth of HD-087 leads to certain abnormalities in pathogen hyphae. It peroxidizes cell membrane lipids, which leads to membrane destruction along with cytoplasm leakage. This broth also restrains germination of the conidia. The activities of the enzymes peroxidase, phenylalanine ammonia-lyase, and β-1,3-glucanase in cucumber leaves were dramatically increased after treated with fermentation broth of HD-087. The levels of chlorophyll and soluble sugars were also found to be increased, with the relative conductivity of leaves being reduced. In short, the metabolites of strain HD-087 can effectively suppress F. oxysporum and trigger induced resistance in cucumber.

An antifungal compound from Trichoderma harzianum SQR-T037 effectively controls Fusarium wilt of cucumber in continuously cropped soil

The aim of this study was to separate antifungal compounds that could effectively be against Fusarium oxysporum f. sp. cucumerinum (FOC) and control Fusarium wilt of cucumber in continuously cropped soil, from a promising biocontrol agent Trichoderma harzianum SQR-T037. One purified antifungal compound was identified as 6-pentyl-α-pyrone (6PAP) using both mass spectrometry and nuclear magnetic resonance spectroscopy. Assay of antifungal activity with a series of 6PAP concentrations (50, 150, 250, 350 and 450 mg L−1) in medium showed that the antifungal activity increased as the concentration increased. At 350 mg L−1 of 6PAP, 73.7% of mycelia growth and 79.6% of conidia germination of FOC was inhibited as compared with the control. Additionally, at a 6PAP concentration of 150 mg L−1, sporulation and fusaric acid production (g g−1 dry mycelia) of FOC decreased by 88.0% and 52.68%, respectively. Furthermore, 6PAP, added as a rate of 350 mg per kg in cucumber continuously cropped soil, could decrease population of indigenous F. oxysporum by 41.2% and control Fusarium wilt of cucumber by 78.1–89.6%, and thus increase dry weight of cucumber seedlings by 60.0–92.6% in pot experiments. The results showed that 6PAP demonstrated antifungal activity against FOC and could control Fusarium wilt in cucumber continuously cropped soil.

Screening and partial characterization of Bacillus with potential applications in biocontrol of cucumber Fusarium wilt

Bacullus strains are effective biocontrol agents of the cucumber wilt caused by Fusarium oxysporum f. sp. Cucumerinum. In this study, a total of 400 Bacillus samples were isolated from surface-sterilized roots of cucumber plants grown in greenhouses and fields, and were screened using a modified gnotobiotic system for their capability in controlling Fusarium wilt of cucumber. A strain designated as B068150 showed a high potential in control of the Fusarium wilt, with biocontrol effectiveness up to 50.68% in seedling stage in greenhouse experiments. Interestingly, B068150 showed no obvious antagonistic activity to F. oxysporum f. sp. Cucumerinum on potato dextrose agar plate. B068150 was identified as Bacillus subtilis by using morphological, physiological, biochemical tests, cellular fatty acids analysis, and Biolog-based substrate utilization test. In addition, 16S rRNA gene and gyrA gene-based phylogenetic analysis illustrated that B068150 exhibits high levels of similarity to known Bacillus species. Therefore B068150 was finally designated as B. subtilis B068150. The pot experiments results in greenhouse indicated that B. subtilis B068150 could be a promising agent in biocontrol of Fusarium wilt of cucumber, which might help to minimize the yield loss of cucumber caused by F. oxysporum f. sp. cucumerinum in north China.