Effects of infection time and moisture on development of ear blight and deoxynivalenol production by Fusarium spp. in wheat

Wheat ears were inoculated with conidia of Fusarium spp. at different growth stages between ear emergence and harvest and moist conditions were maintained for up to 7 days subsequently by mist irrigation. Of the fungi tested (Fusarium culmorum, F. avenaceum, F. tricinctum, F. sporotrichioides and Microdochium nivale), only F. culmorum produced ear blight symptoms and grain samples were found subsequently to contain deoxynivalenol. Most ear infection and deoxynivalenol formation occurred following inoculation at about mid-anthesis. Small amounts of deoxynivalenol were formed and some F. culmorum was isolated even in the absence of ear blight symptoms. An overnight wet period was sufficient to initiate infection and deoxynivalenol formation but both were increased by extending the wet period up to at least 3 days. Recovery of Fusarium spp. from harvested grain was usually possible whether or not symptoms developed. F. culmorum usually persisted and often increased to moderately high levels after storage for 7 wk in a range of moisture conditions.     

Aggressiveness spectrum and genetic variability of Fusarium spp. on rice and wheat varieties

Abstract

A total of 106 Fusarium spp. were isolated from infected roots and soil samples of wheat and rice. Of the 106 isolates, 32 from wheat, and 74 from rice, were isolated. Six Fusarium spp. (F. oxysporum, F. moniliforme, F. poae, F. graminearum, F. tricinctum and F. equiseti) were identified at specie level. In aggressiveness tests Fusarium spp. root rot causing fungi were screened out into different aggressiveness classes according to disease severity scales. The aggressiveness of Fusarium spp. was studied on wheat varieties (Inqalab-91 and chakwal-86) and on rice varieties (Basmati-385 and IRRI-6) under controlled conditions. The overall total number of aggressive isolates was higher in rice than in wheat. However, the percentage of severely aggressive isolates was high in wheat, whereas the percentage of moderately and slightly aggressiveness isolates was high in rice. In rice, five isolates were non-aggressive and on wheat 17 were non-aggressive. Random Amplified Polymorphism DNAs (RAPDs) were used to study the polymorphism and genetic variations within the population of Fusarium spp. that established to study correlation between taxonomical and genetical characters of fungi. Five random primers were used P1 (5′-AGGAGGACCC-3′), P2 (5′-ACGAGGGACT-3′), PE7 (5′-AGATGCAGCC-3′), P14 (5′-CCACAGCACG-3′) and PE20 (5′-AACGGTGACC-3′). Each of the 10-mer primers produced results based on the respective banding patterns they generated in present investigations. Primers distinguished the F. oxysporum, F. moniliforme, F. graminearum, F. tricinctum, F. poa and F. equiseti. All the tested primers yielded amplification products, and that were reproducible. Although there was some intraspecific variation with primers, some strains were similar and some were different in banding pattern. In F. oxysporum, F. moniliforme, F. graminearum, F. tricinctum, F. poa and F. equiseti were seen clustered close to one another but each primer separated them unambiguously. All primer (P1, P2, P14, PE7 and PE20) combination produced 62 bands. All primers have shown interspecific and intraspecific variations in banding patterns.     

Characterization of Fusarium spp. associated with pineapple fruit rot and leaf spot in Peninsular Malaysia

Pineapple (Ananas comosus) is one the important fruit crops planted in Malaysia, and this study was conducted to determine Fusarium spp. associated with diseases of the fruit crop as Fusarium is prevalent in tropical countries. Our objective was to identify and characterize Fusarium spp. associated with pineapple fruit rot and leaf spot mainly found on the fruits and leaves in Peninsular Malaysia. Fusarium isolates (n = 108) associated with pineapple fruit rot and leaf spot were characterized by morphological, molecular and phylogenetic analyses, a mating study and pathogenicity testing. TEF‐1α sequence analysis identified Fusarium proliferatum, Fusarium verticillioides, Fusarium sacchari and Fusarium sp. Mating was successful only between tester strains of F. proliferatum and F. verticillioides. Sexual crosses with standard tester strains showed that 82 isolates of F. proliferatum produced fertile crosses with mating population D (Gibberella intermedia) and three isolates of F. verticillioides were fertile with the tester strain of mating population A (Gibberella moniliformis). All isolates were pathogenic, causing pineapple fruit rot and leaf spot, thus fulfilling Koch's postulates.     

Potential of fungal antagonists for biocontrol of Fusarium spp. in wheat and maize through competition in crop debris

Pathogenic Fusarium spp. cause head blight in wheat or ear rot in maize leading to yield losses and also a reduction in quality due to mycotoxin contamination of the grain. Infected crop residues are the main inoculum source for epidemics. Saprophytic fungi, obtained from cereal tissues or necrotic tissues of other crops, were screened for their ability to colonise wheat straw and maize stalks and to suppress sporulation of pathogenic Fusarium spp. Results of bio-assays conducted under controlled conditions were variable among Fusarium spp. and host substrates for most antagonists tested, such as yeasts, Trichoderma spp. and non-pathogenic Fusarium spp. Isolates of Clonostachys rosea consistently suppressed sporulation of F. culmorum and F. graminearum on wheat straw, and of F. culmorum, F. graminearum, F. proliferatum and F. verticillioides on maize stalks. Isolates of C. rosea, C. cladosporioides and F. equiseti were applied to pieces of maize stalks or flowering ears in preliminary experiments conducted under field conditions. The colonisation of stalk pieces by pathogenic Fusarium spp. was assessed after 9 months. Colonisation of stalk pieces by pathogenic Fusarium spp. was significantly reduced at several sampling dates. However, results obtained with the antagonists were not consistent for all sampling dates and between experiments.     

Contamination of malt barley and wheat by Fusarium graminearum and Fusarium culmorum from the crop years 2001-2003 in eastern Croatia

This study investigated infection levels with Fusarium graminearum and Fusarium culmorum in malt barley and wheat in eastern Croatia. The contamination was surveyed over three consecutive crop years (2001–2003) on five locations for barley and three wheat cultivating locations. F. graminearum loads reached levels of potentially serious threat for the commercial production of malting raw materials in both cereals (up to 29.1%). On the other hand, the mean percentage of kernels infected with F. culmorum was low to medium (up to 6.1%). The fungal invasions for years and locations were affected by meteorologic and other environmental factors and the pattern seemed to be consistent with species-specific optimal conditions reported by other authors.     

秸秆及秸秆黑炭对小麦养分吸收及棕壤酶活性的影响

通过小麦盆栽试验,研究了玉米秸秆及其秸秆黑炭施加对小麦养分吸收利用和棕壤酶活性的影响。试验设对照(CK),黑炭(B),秸秆还田(S),尿素(U),尿素+黑炭(UB)及尿素+秸秆还田(US)6个处理,各处理3次重复。结果表明:无氮肥施入下,B处理较CK和S处理籽粒产量显著提高99.4%和77.7%,小麦地上部氮、磷、钾吸收累积量分别显著提高94.1%—140.9%,55.4%—66.3%和53.1%—72.6%;有氮肥施入下,UB和US处理较U处理提高籽粒产量8.2%—8.8%,小麦地上部氮、磷、钾吸收累积量分别显著提高14.3%—27.8%,19.6%—30.9%和24.4%—40.9%。秸秆及秸秆黑炭施加处理的氮素利用率显著提高21.4%—41.7%。黑炭施加显著提高土壤中有机碳、NH+4-N、NO-3-N和速效钾含量;在施氮条件下,秸秆还田显著提高土壤中NO-3-N含量;秸秆及黑炭施加对有效磷含量无显著影响。秸秆还田显著提高了土壤脱氢酶、过氧化氢酶、脲酶和中性磷酸酶活性;施加黑炭也明显提高了土壤脱氢酶和脲酶活性,但抑制过氧化氢酶和中性磷酸酶活性。土壤脲酶活性与土壤有机碳、无机氮含量呈显著正相关,表明土壤酶可反映土壤肥力水平。     

Observations on the maintenance and measurement of soil water in simple pot experiments and its effects on seed-borne Fusarium culmorum seedling blight of winter wheat

A simple method for maintaining and measuring soil water and the relationship between soil water and seed-borne Fusarium culmorum seedling blight of wheat was investigated under controlled environmental conditions to develop reproducible assay conditions for epidemiological studies and the testing of fungicide seed treatments. For reproducibility, soil matric potential (ψ_m) was used to define soil water, and a range of watering regimes were tested. Treatments were watered to either a maximum ψ_m or to maintain a mean ψ_m in order to establish which parameter best described the effect that soil water had on the incidence of disease symptoms. The severity of disease symptoms was closely related to the mean soil water status and not the maximum ψ_m value. Watering intervals, ranging from three times a day to once every three days, did not affect this relationship. The percentage of seedlings showing symptoms after emergence (i.e. localised or extensive necrotic lesions) was inversely related to the mean ψ_m. With increasing soil dryness (mean ψ_m from -0.14 MPa to -0.17 MPa) the percentage of seedlings with post-emergence symptoms decreased from 50% to 20%. However, as the mean ψ_m changed from -0.14 MPa to -0.17 MPa the percentage of seedlings dying before emergence increased from 25% to 55% in direct proportion to ψ_m. Overall the incidence of infection as indicated by the total number of seedlings showing symptoms either before or after emergence remained relatively constant, and was not significantly related to mean ψ_m.     

Quantitative Fusarium spp. and Microdochium spp. PCR assays to evaluate seed treatments for the control of Fusarium seedling blight of wheat

AIMS: To develop sensitive quantitative PCR assays for the two groups of pathogens responsible for Fusarium seedling blight in wheat: Fusarium group (Fusarium culmorum and Fusarium graminearum) and Microdochium group (Microdochium nivale and Microdochium majus); and to use the assays to assess performance of fungicide seed treatments against each group. METHODS AND RESULTS: Primers conserved between the species within each group were used to develop competitive PCR assays and used to quantify DNA of each group in wheat seed produced from inoculated field plots. Seed was used in seed treatment efficacy field experiments and the amount of DNA of each group was determined in emerged seedlings. The performance of treatments towards each group of pathogens was evaluated by comparison of the reduction in DNA in seedlings emerged from treated seed compared with untreated seed. CONCLUSIONS: DNA from the two groups of pathogens causing Fusarium seedling blight of wheat can be quantified separately using the competitive PCR assays. These assays show improved sensitivity compared with those previously reported for the individual species and allowed the quantification of pathogen DNA in seed and seedlings. Significant reductions in pathogen DNA were evident for each seed treatment. SIGNIFICANCE AND IMPACT OF THE STUDY: Quantification of DNA for each group allows the evaluation of seed treatment performance towards the two components of Fusarium seedling blight disease complex. The approach taken and the assays developed in this study will be of use for the study of other Fusarium disease complexes and their control. Based on the results reported here on the seedling stage of crop development, further studies that examine the control of seed-borne pathogens through fungicide seed treatments throughout the growing season are warranted.     

Progression of mycotoxin and nutrient concentrations in wheat after inoculation with Fusarium culmorum

The objective of this study was to follow the mycotoxin formation and changes in nutrient composition of wheat (cv. Ritmo) artificially inoculated with Fusarium culmorum. From anthesis until harvest, samples were taken once a week from the inoculated and control plots. The investigations were focused on monitoring the progression of the contamination of the wheat kernels with deoxynivalenol (DON) and zearalenone (ZON). Both the uncontaminated control kernels and the contaminated kernels were examined also for the presence of zearalenone-4-beta-D-glucopyranoside and several trichothecenes at harvest. Furthermore, the impact of the Fusarium inoculation on some nutrients as starch, crude protein, amino acid composition, crude ash, non starch polysaccharides (NSP) as well as viscosity and thousand seed weight (TSW) was examined. Also proteolytic and amylolytic activity as well as the NSP-degrading enzyme activities of inoculated and control samples were analysed at the time of harvest. DON was detected in higher concentrations and in earlier stages, while ZON was found later and in smaller amounts. On average 7.79?mg/kg DM of DON and 100?μg/kg DM of ZON were found in the inoculated kernels at the time of harvest. Neither in the contaminated nor in the control samples glucose conjugates of ZON (Zearalenone-4-beta-D-glucopyranoside) were detected. Moreover, the infection with Fusarium culmorum had pronounced effects on some quality parameters. The crude protein content of the inoculated kernels showed significantly higher values over the whole period compared to the control kernels. The protein content of the inoculated kernels amounted 13.9% DM at harvest, while only a concentration of 12.5% DM was detected in the control samples. Similarly, in almost all stages of development the crude ash content of inoculated samples was higher than in control samples. These distinct differences in kernel composition resulted possibly from the changes of the thousand seed weight. In the present work the grain harvested from the control plots showed a significantly higher TSW (24.2?g) as compared to their inoculated counterparts (15.5?g). Despite lower extract viscosity of inoculated samples at time of harvest, the content of soluble NSP of inoculated plots was higher than in control samples at the same time. Moreover, inoculation resulted in markedly increased activities of protease, amylase and several NSP-degrading enzyme activities. This would suggest that the cell wall penetrating properties of the fungus itself and/or that the fungus induced alterations of the metabolic activity of the embryo or other constituents of the wheat kernel could be responsible.     

Evaluation of Streptomyces spp. and Bacillus spp. for biocontrol of Fusarium wilt in chickpea (Cicer arietinum L.)

A study was carried out to test direct and indirect antagonistic effect against Fusarium wilt, caused by Fusarium oxysporum f. sp. ciceri (FOC), and plant growth-promoting (PGP) traits of bacteria isolated from rhizosphere soils of chickpea (Cicer arietinum L.). A total of 40 bacterial isolates were tested for their antagonistic activity against FOC and of which 10 were found to have strong antagonistic potential. These were found to be Streptomyces spp. (five isolates) and Bacillus spp. (five isolates) in the morphological and biochemical characterisation and 16S rDNA analysis. Under both greenhouse and wilt sick field conditions, the selected Streptomyces and Bacillus isolates reduced disease incidence and delayed expression of symptoms of disease, over the non-inoculated control. The PGP ability of the isolates such as nodule number, nodule weight, shoot weight, root weight, grain yield and stover yield were also demonstrated under greenhouse and field conditions over the non-inoculated control. Among the ten isolates, Streptomyces sp. AC-19 and Bacillus sp. BS-20 were found to have more potential for biocontrol of FOC and PGP in chickpea. This investigation indicates that the selected Streptomyces and Bacillus isolates have the potential to control Fusarium wilt disease and to promote plant growth in chickpea.     

Potential of endophytic Streptomyces spp. for biocontrol of Fusarium root rot disease and growth promotion of tomato seedlings

Sixteen endophytic actinobacteria isolated from roots of native plants were evaluated for their antagonistic potential against soil-borne phytopathogenic fungi. Among them, three strong antagonistic isolates were selected and characterised for in vitro plant-growth-promoting and biocontrol traits, including production of hydrogen cyanide, indole-3-acetic acid and siderophores, chitinase and β-1,3-glucanase activities, and inorganic phosphate solubilisation. In all trials, the strain Streptomyces sp. SNL2 revealed promising features. The selected actinobacteria were investigated for the biocontrol of Fusarium oxysporum f. sp. radicis lycopersici and for growth promotion of tomato (Solanum lycopersicum L. cv. Aïcha) seedlings in autoclaved and non-autoclaved soils. All seed-bacterisation treatments significantly reduced the root rot incidence compared to a positive control (with infested soil), and the isolate SNL2 exhibiting the highest protective activity. It reduced the disease incidence from 88.5% to 13.2%, whereas chemical seed treatment with Thiram® provided 14.6% disease incidence. Furthermore, isolate SNL2 resulted in significant increases in the dry weight, shoot and root length of seedlings. 16S rDNA sequence analysis showed that isolate SNL2 was related to Streptomyces asterosporus NRRL B-24328^T (99.52% of similarity). Its interesting biocontrol potential and growth enhancement of tomato seedlings open up attractive uses of the strain SNL2 in crop improvement.     

Effects of vanillin on the community structures and abundances of Fusarium and Trichoderma spp. in cucumber seedling rhizosphere

Soil microbial communities are crucial to the functioning of agricultural systems but little information is available on the effects of allelochemicals on soil microorganisms in vivo. Cucumber seedlings grown in soil were treated with different concentrations of vanillin (0.02–0.2?μmol/g soil), a phenolic compound with autotoxic activity. The community structures and abundances of Fusarium and Trichoderma spp. in cucumber rhizosphere were analyzed by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis and quantitative PCR, respectively. Results showed that vanillin changed the community structures of Fusarium and Trichoderma spp. Vanillin decreased the number of bands of Fusarium spp., but increased the number of bands, Shannon–Wiener and evenness indices of Trichoderma spp. (p?Fusarium and Trichoderma spp. (p?Fusarium and Trichoderma spp., and that these two microbial groups showed different responses to vanillin.     

Detection of Races 1 and 2 of Fusarium solani f. sp. cucurbitae and their Distribution in Watermelon Fields in Tunisia

A crown, foot and fruit rot of watermelon has been observed in most of the watermelon production areas in Tunisia. A survey conducted from 2000 to 2001 allowed the isolation of 291 isolates which were identified as Fusarium solani. These isolates were identified as F. solani f. sp. cucurbitae (Fsc) and races 1 and 2 characterized on the basis of pathogenicity tests on watermelon seedlings and muskmelon fruits. These results were confirmed by counts of the number of septa in the macroconidia. About 271 isolates were identified as Fsc race 1, 12 isolates were identified as Fsc race 2 and eight isolates were not pathogenic. Race 1 is widely distributed in watermelon production areas in Tunisia and race 2 has a lower incidence but it is present in the north, the middle and southern Tunisian watermelon cropping areas. Additionally, a study to compare the virulence of 122 isolates of Fsc race 1 showed different degrees of virulence among them. This is the first report of Fsc races 1 and 2 in Tunisia.     

Effects of rhamnolipid on the cellulase and xylanase in hydrolysis of wheat straw

The effects of biosurfactant rhamnolipid (RL) and chemical surfactant Triton X-100 on the production of cellulases and xylanase from Penicillium expansum (P. expansum) in untreated, acid- and alkali-pretreated wheat straw submerged fermentations were studied, and the influences on the activity and stability of Cellulase R-10 were also investigated. The results showed that RL and Triton X-100 enhanced the activities of cellulases and xylanase to different extents and the stimulatory effects of RL were superior to those of Triton X-100. During the peak enzyme production phase, RL (60 RE mg/l) increased cellulases activities by 25.5-102.9%, in which the raise of the same enzyme in acid-pretreated straw broths was the most. It was found that the reducing sugars by hydrolyzing wheat straw with Cellulase R-100 were not visibly increased after adding RL. However, it distinctly protected Cellulase R-10 from degradation or inactivation, keeping the reducing sugars yield at about 17%.     

Two different PCR approaches for universal diagnosis of brown rot and identification of Monilinia spp. in stone fruit trees

AIMS: To design a protocol for the universal diagnosis of brown rot by polymerase chain reaction (PCR) in plant material and subsequently Monilinia spp. identification. METHODS AND RESULTS: Primers for discrimination of Monilinia spp. from other fungal genera by PCR were designed following a ribosomal DNA analysis. Discrimination among species of Monilinia was subsequently achieved by developing primers using SCAR (Sequence Characterised Amplified Region) markers obtained after a random amplified polymorphic DNA study. In addition, an internal control (IC) based on the utilization of a mimic plasmid was designed to be used in the diagnostic protocol of brown rot to recognize false negatives due to the inhibition of PCR. CONCLUSIONS: The four sets of primers designed allowed detection and discrimination of all Monilinia spp. causing brown rot in fruit trees. Addition of an IC in each PCR reaction performed increased the reliability of the diagnostic protocol. SIGNIFICANCE AND IMPACT OF THE STUDY: The detection protocol presented here, that combined a set of universal primers and the inclusion of the plasmid pGMON as an IC for diagnosis of all Monilinia spp., and three sets of primers to discriminate the most important species of Monilinia, could be an useful and valuable tool for epidemiological studies. The method developed could be used in programmes to avoid the spread and introduction of this serious disease in new areas.     

施用保水剂和稻草覆盖对作物和土壤的效应

在江苏淮北东海县季节性干旱严重的岭沙土上,开展了施用保水剂和稻草覆盖对保持土壤水分和作物产量的效应的比较试验,保水剂和稻草的用量各分4级,分别为1,2,3,6g.kg^-1土和1500,3000,4500,6000kg/hm^-2,结果表明,两者均可促进小麦生长,提高当季及后茬作物产量,覆盖稻草和施用保水剂分别比对照增产小麦12．5％和10％,其作用机制在于两者均能减少土壤水分蒸发,提高土壤持水能力,增加有效水供应,并对土壤容重,温度及养分状况有一定的改善作用。     

Relationship of in vitro and in planta screening: improving the selection process for biological control agents against Fusarium root rot in row crops

Fusarium root rot in row crops is typically managed by cultural practices and fungicide seed treatments. Biological control using microbial agents is another option but needs further development for improved disease management. Screening to identify biocontrol agents are crucial. However, relationships among the steps and how to improve the screening process are unresolved questions. Strains of Burkholderia (4), Bacillus (5) and Trichoderma (26) were studied in vitro against six Fusarium pathogens. All the bacteria and five selected Trichoderma strains were tested in planta in the greenhouse against diseases of Fusarium graminearum and Fusarium oxysporum. Burkholderia ambifaria C628, Bacillus simplex R180, and all Trichoderma isolates showed high reduction in disease levels in corn, soybean and wheat, ranging from 16 to 63%. Responses of the biocontrol agents during in vitro and in planta screening did not always correlate. In vitro and in planta tests should be considered independently in selecting biocontrol candidates.     

Selection of bacteria able to control Fusarium oxysporum f. sp. radicis-lycopersici in stonewool substrate

AIMS: Tomato foot and root rot (TFRR), caused by Fusariumoxysporum f. sp. radicis-lycopersici (Forl), is an economically important disease of tomato. The aim of this study was to develop an efficient protocol for the isolation of bacteria, which controls TFRR based on selection of enhanced competitive root-colonizing bacteria from total rhizosphere soil samples. METHODS AND RESULTS: A total of 216 potentially enhanced bacterial strains were isolated from 17 rhizosphere soil samples after applying a procedure to enrich for enhanced root tip colonizers. Amplified ribosomal DNA restriction analysis, in combination with determination of phenotypic traits, was introduced to evaluate the presence of siblings. One hundred sixteen strains were discarded as siblings. Thirty-eight strains were discarded as potential pathogens based on the sequence of their 16S rDNA. Of the remaining strains, 24 performed equally well or better than the good root colonizer Pseudomonas fluorescens WCS365 in a competitive tomato root tip colonization assay. Finally, these enhanced colonizers were tested for their ability to control TFRR in stonewool, which resulted in seven new biocontrol strains. CONCLUSIONS: The new biocontrol strains, six Gram-negative and one Gram-positive bacteria, were identified as three Pseudomonas putida strains and one strain each of Delftia tsuruhatensis, Pseudomonas chlororaphis, Pseudomonas rhodesiae and Paenibacillus amylolyticus. SIGNIFICANCE AND IMPACT OF THE STUDY: We describe a fast method for the isolation of bacteria able to suppress TFRR in stonewool, an industrial plant growth substrate. The procedure minimizes the laborious screens that are a common feature in the isolation of biocontrol strains.     

免耕条件下秸秆覆盖对旱地小麦田土壤团聚体的影响

设2个秸秆覆盖时期(全程覆盖、生育期覆盖)和3个覆盖量(3000、6000和9000kg·hm-2),以全程不覆盖为对照,研究陕西渭北旱塬免耕条件下秸秆覆盖对小麦田土壤团聚体的影响.结果表明:在0～40 cm土层,随土层的加深,＞5 mm径级的土壤团聚体含量逐渐增加,＜5 mm径级的土壤团聚体含量逐渐减小;各覆盖处理中,＞0.25 mm径级的机械稳定性团聚体和水稳性团聚体的含量均显著大于对照,分别增加13.0％～26.4％和18.6％～45.6％,其中,6000 kg·hm-2秸秆覆盖处理的增幅最大;秸秆覆盖提高了土壤有机质含量,土壤有机质含量与＞0.25 mm径级的土壤水稳性团聚体含量呈显著正相关;各秸秆覆盖量处理均降低了土壤不稳定团粒指数,以6000 kg·hm-2秸秆覆盖处理的土壤不稳定团粒指数最小.表明秸秆覆盖可显著增加0 ～40 cm土层＞0.25 mm径级的土壤团聚体和有机质含量,提高土壤结构稳定性,并且以6000 kg·hm-2覆盖量的处理效果最佳,该覆盖量可以作为渭北旱塬小麦田合理的秸秆覆盖模式应用于农业生产中.     

Analysis of genetic variability of Fusarium oxysporum f. sp. cepae the causal agent of basal rot on onion using RAPD markers

Genetic variability among isolates of Fusarium oxysporum f. sp. cepae was obtained from different onion-growing areas of Tamil Nadu, India. Random amplified polymorphic DNA (RAPD) analysis was carried out using 12 random primers, each of them consisting of 10 base pairs. Four out of the 12 primers were differentiated between some of the tested F. oxysporum f. sp. cepae isolates. Analysis of the genetic coefficient matrix derived from the scores of RAPD profile showed that minimum and maximum per cent similarities among the F. oxysporum f. sp. cepae isolates were in the range of 14–85%. Cluster analysis, using the unweighted pair-group method with arithmetic average, clearly separated the isolates into two clusters (A and B) confirming the genetic diversity among the isolates of F. oxysporum f. sp. cepae from onion.