Isolates Of Fusarium Oxysporum Research Articles

Enhancement of pectinase production by ultraviolet irradiation and diethyl sulfate mutagenesis of a Fusarium oxysporum isolate.

Fusarium oxysporum strain BM-201 was treated with ultraviolet (UV) radiation to obtain a high pectinase-producing strain. Mutant UV-10-41 was obtained and then treated by diethyl sulfate. Next, the mutant UV-diethyl sulfate-43 derived from UV-10-41 was selected as high pectinase-producing strain. Mutant UV-diethyl sulfate-43 was incubated on slant for 10 generations, demonstrating that the pectinase-producing genes were stable. Pectinase activity reached 391.2 U/mL, which is 73.6% higher than that of the original strain.

Fusarium oxysporum f. sp. radicis‐vanillae is the causal agent of root and stem rot of vanilla

Root and stem rot (RSR) is a very detrimental disease of vanilla worldwide. Fusarium oxysporum is frequently associated with the disease but other Fusarium species are also reported. In this international study, 52 vanilla plots were surveyed in three of the most important vanilla producing countries (Madagascar, Reunion Island and French Polynesia) in order to determine the aetiology of RSR disease. Subsets from the 377 single‐spored Fusarium isolates recovered from rotten roots and stems in the surveys were characterized by molecular genotyping (EF1α and IGS gene sequences) and pathogenicity assays on Vanilla planifolia and V. ×tahitensis, the two commercially grown vanilla species. Fusarium oxysporum was shown to be the principal species responsible for the disease, representing 79% of the isolates recovered from the RSR tissues, 40% of which induced severe symptoms on inoculated plantlets. Fusarium oxysporum isolates were highly polyphyletic regardless of geographic origin or pathogenicity. Fusarium solani, found in 15% of the samples and inducing only mild symptoms on plantlets, was considered a secondary pathogen of vanilla. Three additional Fusarium species were occasionally isolated in the study (F. proliferatum, F. concentricum and F. mangiferae) but were nonpathogenic. Histopathological preparations observed in wide field and multiphoton microscopy showed that F. oxysporum penetrated the root hair region of roots, then invaded the cortical cells where it induced necrosis in both V. planifolia and V. ×tahitensis. The hyphae never invaded the root vascular system up to 9 days post‐inoculation. As a whole, the data demonstrated that RSR of vanilla is present worldwide and that its causal agent should be named F. oxysporum f. sp. radicis‐vanillae.

Antifungal Activity of a Synthetic Cationic Peptide against the Plant Pathogens Colletotrichum graminicola and Three Fusarium Species.

A small cationic peptide (JH8944) was tested for activity against a number of pathogens of agricultural crops. JH8944 inhibited conidium growth in most of the tested plant pathogens with a dose of 50 μg/ml, although one isolate of Fusarium oxysporum was inhibited at 5 μg/ml of JH8944. Most conidia of Fusarium graminearum were killed within 6 hours of treatment with 50 μg/ml of JH8944. Germinating F. graminearum conidia required 238 μg/ml of JH8944 for 90% growth inhibition. The peptide did not cause any damage to tissues surrounding maize leaf punctures when tested at a higher concentration of 250 μg/ml even after 3 days. Liposomes consisting of phosphatidylglycerol were susceptible to leakage after treatment with 25 and 50 μg/ml of JH8944. These experiments suggest this peptide destroys fungal membrane integrity and could be utilized for control of crop fungal pathogens.

An in vitro antagonistic activity evaluation of rhizobacteria against Fusarium oxysporum f. sp. radicis-lycopersici (Forl) isolated from the Algerian west.

The use of biological antagonists is a promising technique for the protection of plants without having a fatal effect on the environment. The in vitro confrontation tests is an obligatory step for the selection of successful antagonistic agents, what has ends in our study to the selection of two rhizobacteria: Bacillus subtilis and Pseudomonas fluorescens, isolated from the rhizosphere of tomato healthy plants and which were tested for their in vitro inhibitive power against five isolates of Fusarium oxysporum f. sp. radicis-lycopersici (Forl). The results of the direct confrontation on different culture media demonstrated that rhizobacteria have an inhibitive effect on the pathogenic, while noticing a performance of P. fluorescens with an inhibition which varies between 73,77 and 80 %, comparing with 56,36 and 60,46 % for B. subtilis. The inhibition by volatile substances of P. fluorescens varies between 25 and 39,53 %, compared with 18,86 and 32,55 % by volatile substances of B. subtilis. Rhizobacterial cell-free supernatant showed an inhibition from the first until the seventh incubation day against the five fungal isolates, when mycelia growth reaches 5±0,2 cm in presence of P. fluorescens cell free supernatant, and it reaches 5,9±0,3 cm in presence of B. subtilis cell free supernatant compared with 8,5 cm on control plates without rhizobacteria cell free supernatant.

VARIABILIDADE GENÉTICA DE ISOLADOS DE Fusarium solani e Fusarium oxysporum f. sp.passiflorae ASSOCIADOS AO MARACUJAZEIRO

Determinou-se a variabilidade genética de 37 isolados de Fusarium solani e 13 isolados de Fusarium oxysporum f. sp. passiflorae patogênicos ao maracujazeiro por meio do uso de marcadores ISSR e RAPD. Os isolados foram obtidos de maracujazeiros com sintomas de murcha, encontrados nas principais regiões produtoras do Norte Mineiro e no município de Sebastião Laranjeira – BA. Após obtenção de culturas monospóricas, os isolados tiveram seus DNAs extraídos e submetidos à reação de PCR. Foram selecionados nove primers ISSR e nove primersRAPD, e a análise de dados foi realizada, utilizando-se do coeficiente de similaridade de Jaccard. A partir da amplificação com os primers ISSR e RAPD, foram obtidos 121 e 126 locos, respectivamente, sendo quetodos apresentaram polimorfismo entre, pelo menos, dois isolados. Demonstraram-se, por meio das análises ISSR, índice de similaridade genética interespecífica de 0,15 e índices de variabilidade intraespecífica de 0,27 a 0,92 para F. solani e de 0,30 a 0,89 para F. oxysporum. f. sp. passiflorae. Já, por meio das análises RAPD, foram gerados índice de similaridade genética interespecífica de 0,11 e índices de variabilidade intraespecífica de 0,17 a 0,79 para F. solani e de 0,21 a 0,73 para F. oxysporum f. sp. passiflorae. Os isolados de F. oxysporum f. sp. passiflorae e F. solani agruparam-se em dois clustersdistintos, e observou-se uma alta variabilidade intraespecífica nas duas espécies.

Production and characterization of alien chromosome addition lines in Allium fistulosum carrying extra chromosomes of Allium roylei using molecular and cytogenetic analyses

Allium roylei was employed for the production of alien chromosome addition lines in A. fistulosum. Interspecific hybridization between A. fistulosum and A. roylei successfully produced F1 hybrids. Chromosome doubling of an F1 hybrid was carried out to produce amphidiploids. After two times backcrossing of the amphidiploids with A. fistulosum, a BC2 generation was obtained with chromosome numbers (2n) ranging from 16 to 23. Alien monosomic addition lines (AMAL, FF + nR, 2n = 17) appeared with the highest frequency. Furthermore, multiple addition lines (MAL, 2n = 18–23) were also observed with lower frequencies. Five AMALs (FF + 1R, +3R, +4R, +5R, and +8R) and ten MALs (2n = 18–23) were characterized using isozyme and DNA markers. The extra chromosomes from A. roylei clearly altered the biochemical characteristics of the MALs. Variations in sugar, cysteine sulfoxide, and flavonoid contents were observed among the MALs in various amounts. Allium fistulosum–A. roylei allotriploids (2n = 24, FFR) showed significantly higher saponin content and antifungal activities of saponin extracts against isolates of Fusarium oxysporum f. sp. cepae in comparison with A. fistulosum. This first report of A. fistulosum–A. roylei addition lines opens the possibility of developing novel A. fistulosum cultivars with enhanced nutritional value and disease resistance.

Native Bacillus amyloliquefaciens W2 as a potential biocontrol for Fusarium oxysporum R1 causing corm rot of Crocus sativus

Fusarium corm rot is the major destructive disease of Crocus sativus, a perennial herb whose stigma forms the commercially important spice “saffron”. In the present study we isolated a native Bacillus strain with antagonistic activity against a Fusarium oxysporum isolate causing the disease. Three fungi, Fusarium oxysporum, F. solani and Penicillium sp., were isolated from the corms showing classical symptoms of rot collected from saffron fields in the valley of Kashmir, India. The fungi were characterized using conidial morphology and molecular phylogeny. Among 400 bacterial isolates selected randomly from the rhizosphere and bulk soil of saffron fields, Bacillus amyloliquefaciens strain W2 was found effective against corm rot caused by F. oxysporum R1. Antagonistic activity of B. amyloliquefaciens W2 was confirmed in vitro using well diffusion and dual culture assay as well as in vivo by pot trials. The disease incidence in pot assays was 93 and 40 % in absence and presence of B. amyloliquefaciens W2 respectively. B. amyloliquefaciens W2 can be used as a potent biofungicide for corm rot diseases in C. sativus.

Antimicrobial activities of selected essential oils against Fusarium oxysporum isolates and their biofilms

Fusarium infections, such as keratitis, are becoming increasingly difficult to control due to the build-up of resistance of fungi towards conventional antibiotics. Resistance is further enhanced by their ability to form fungal biofilms. Poor storage conditions and inadequate cleaning of contact lenses often lead to corneal infections. The solution to problems associated with contamination and resistance to antimicrobials could lie in the discovery of new, affordable, efficacious antimicrobial compounds. The purpose of this study was to evaluate the antifungal and antibiofilm properties of selected essential oils. The plant-based essential oils were evaluated for in vitro antifungal activity against Fusarium spp. using the Toxic Medium Assay (TMA) for preliminary screening. Clove and thyme oils, as well as pure citral, eugenol and thymol at 500μL/L, exhibited the highest antimicrobial activity against Fusarium isolates. Antibiofilm capacity was investigated using soft contact lenses as substrate, while confocal laser scanning microscopy (CLSM) was used for visual observation of biofilm architecture. Although severe damage to the lens was observed when the essential oils were applied at 500μL/L, no visible alteration of the contact lenses was detected at 50μL/L and therefore the antibiofilm property of thyme and clove EOs was evaluated at this concentration. Clove and thyme oils prevented cell attachment, biofilm development and caused total inhibition of biofilm formation on soft contact lenses. The use of diluted clove and thyme oils could therefore be an option to prevent biofilm formation of soft contact lenses.

Chemical variability of essential oils of Protium colombianum from two tropical life zones and their in vitro activity against isolates of Fusarium

There is considerable interest in finding re- placements for the synthetic fungicides and preservatives that are currently used to control fungal pathogens; how- ever, any alternative compounds must be safe and must prevent the development of microbial resistance. In this regard, essential oils have received special attention. Pro- tium colombianum Cuatrecasas is an endemic tree found in tropical rainforests and possesses aromatic and resinous characteristics. To date, there have been no reports con- cerning the chemistry of this species, which belongs to a genus that represents an interesting source of essential oils that are occasionally used as antimicrobial agents. There- fore, the chemical composition of the essential oils found in P. colombianum collected from two life zones over a five-month period was analyzed using gas-chromatogra- phy/mass-spectrometry. A total of 92 components, com- prising 97.7-99.9 % of the total composition, were identified based on their mass spectra and the retention indices. Precedence markers were identified for each life zone, and seasonality affected the samples from one life zone when rainfall was maximum. The in vitro activity against Fusarium oxysporum isolates from carnation and chrysanthemum, as well as a Fusarium solani isolate from chrysanthemum, was tested by determining the minimum inhibitory concentration. Assays using essential oils and control substances showed that terpenoid and phenolic compounds are mainly responsible for the observed anti- fungal activity. These results suggest that P. colombianum essential oils exhibit cytotoxicity against Fusarium isolates and that the search for new sources of anti-fungal essential oils should include sources that contain different ratios of terpenoid and phenolic compounds.

First Report of Fusarium Root Rot Caused by Fusarium oxysporum Infecting Pigmented Grapefruit Trees in Turkey

HomePlant DiseaseVol. 99, No. 4First Report of Fusarium Root Rot Caused by Fusarium oxysporum Infecting Pigmented Grapefruit Trees in Turkey PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Fusarium Root Rot Caused by Fusarium oxysporum Infecting Pigmented Grapefruit Trees in TurkeyF. Baysal-Gurel and A. CinarF. Baysal-GurelSearch for more papers by this author and A. CinarSearch for more papers by this authorAffiliationsAuthors and Affiliations F. Baysal-Gurel , Department of Plant Pathology, The Ohio State University, OARDC, Wooster 44691 A. Cinar , Department of Plant Protection, Faculty of Agriculture, Cukurova University, Balcali, Adana, Turkey 01330. Published Online:1 Apr 2015https://doi.org/10.1094/PDIS-07-14-0746-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Pigmented grapefruit trees (Citrus paradisi Macf. cvs. Star ruby and Rio red) grafted on sour orange (Citrus aurantium L.) exhibiting root rot symptoms have been observed in three orchards in Adana, Turkey, since 1996. Symptoms were decay of roots and aboveground parts (below the grafting point) without oozing gum and vascular discoloration. Infected trees showed reduced vigor and chlorosis on the foliage. The disease incidence was nearly 5 to 10% in each orchard. Nine diseased root parts from nine different plants were surface-sterilized with 1% NaClO for 2 min and cultured on Fusarium-selective medium (3) at 25°C for 1 week. The culture was transferred to potato dextrose agar (PDA) to determine cultural characteristics. Nine isolates consistently yielded white to purple aerial hyphae and produced abundant oval to ellipsoidal, unicellular microconidia (2.2 to 4.1 × 4.3 to 11.0 μm) borne in false heads on short monophialidic conidiophores, three-to-five-septate macroconidia with pedicellate bases (2.2 to 5.7 × 18.7 to 42.8 μm), and chlamydospores (2). To confirm pathogen identity, total DNA was extracted directly from fungal mycelium, using the PowerSoil DNA isolation kit (MO BIO Laboratories, Inc., Carlsbad, CA). The ribosomal DNA internal transcribed spacer (ITS) region was amplified by PCR using the primer pair ITS1 and ITS4 (4) and sequenced. The sequence, deposited in GenBank (Accerssion No. KP119604), was 99% identical to that of Fusarium oxysporum isolates from Spain (KC427029) and China (JN232163). Morphological and cultural characteristics and PCR confirmed the identity of the causal agent as F. oxysporum Schlechtend.:Fr. Ten 14-month-old Star ruby and Rio red plants, grafted on sour orange and transplanted into steam-sterilized potting mix, were drench-inoculated with a conidial suspension (1 × 106 conidia/ml and 50 ml/plant) of a selected isolate (CU2-97) harvested from a 7-day-old culture on PDA. Plants were maintained in a greenhouse from a low of 20°C at night to a high of 25°C during the day until symptoms appeared. Ten control plants from each pigmented grapefruit were drenched with sterilized water and maintained in the same greenhouse. Three months after inoculation, roots and aboveground parts below the grafting point of the grapefruit plants developed necrotic areas on all inoculated seedlings, and fungus was re-isolated from root parts. All control plants remained disease-free, and no fungus was re-isolated. F. oxysporum was reported infecting sweet orange and tangerines grafted on sour orange in Tunisia in 2014 (1). To our knowledge, this is the first report of Fusarium root rot caused by F. oxysporum infecting pigmented Star ruby and Rio red grapefruit grafted on sour orange in Turkey. This indicates that grapefruit trees grafted on sour orange could be at risk for infection of this potentially destructive disease in Turkey.

Characterization of Trichoderma species isolated in Ecuador and their antagonistic activities against phytopathogenic fungi from Ecuador and Japan

Native Trichoderma spp. were isolated from agricultural fields in several regions of Ecuador. These isolates were characterized via morphological observation as well as molecular phylogenetic analysis based on DNA sequences of the rDNA internal transcribed spacer region, elongation factor-1α gene and RNA polymerase subunit II gene. Fifteen native Trichoderma spp. were identified as T. harzianum, T. asperellum, T. virens and T. reesei. Some of these strains showed strong antagonistic activities against several important pathogens in Ecuador, such as Fusarium oxysporum f. sp. cubense (Panama disease) and Mycosphaerella fijiensis (black Sigatoka) on banana, as well as Moniliophthora roreri (frosty pod rot) and Moniliophthora perniciosa (witches’ broom disease) on cacao. The isolates also showed inhibitory effects on in vitro colony growth tests against Japanese isolates of Fusarium oxysporum f. sp. lycopersici, Alternaria alternata and Rosellinia necatrix. The native Trichoderma strains characterized here are potential biocontrol agents against important pathogens of banana and cacao in Ecuador.

Detection and quantification of onion isolates of Fusarium oxysporum f. sp. cepae in onion plant

Fusarium oxysporum f. sp. cepae (FOC) isolated from onion basal rot possessed a SIX3 homolog (FocSIX3) with 91.4 % identity to the SIX3 gene (FolSIX3) of F. oxysporum f. sp. lycopersici (FOL). A primer pair (P1) was designed to detect onion FOC based on differences in nucleotide sequences between FocSIX3 and FolSIX3. P1 amplified a 106-bp-long DNA segment only from FOC isolates pathogenic to onions, but not from FOC isolated from either Welsh onion or F. oxysporum strains belonging to formae speciales other than cepae. Real-time quantitative PCR with P1 was developed to quantify onion root- and basal-plate-colonizing FOC.

Genetic and phenotypic differences of Fusarium oxysporum f. sp. citri isolated from sweet orange and tangerine

Fusarium oxysporum f. sp citri is a new soil-borne pathogen of mature citrus trees in Tunisia. ISSR and RAPD markers were used in this study to characterize strains of Fusarium oxysporum from citrus in Tunisia. Pathogenicity assays revealed that Fusarium oxysporum isolates caused from 32 to 95 % disease on seedlings of Citrus aurantium. Results showed that pathogenic isolates were classified into two groups on the basis of ISSR and RAPD fingerprints, suggesting a level of genetic specificity and diversity not previously identified on Fusarium oxysporum f. sp citri. Cluster analysis, principal coordinate analysis and population structure indicated that the different isolates appears to be related only to the host. Potential primers related to ISSR markers could be selected to characterize Tunisian strains of Fusarium oxysporum and determine genetic differences of the pathogen virulence. With this investigation we characterize Fusarium wilt on citrus trees by the mean of ISSR and RAPD markers.

Studies on Fusarium wilt Disease of Cucumber

Eight isolates of Fusarium oxysporum f.sp. cucumerinum; the causal organism of Fusarium wilt of cucumber plants; were isolated from wilted cucumber plant samples collected from eight different localities in Egypt . These isolates were pathogenic to the susceptible cucumber cultivar “Biet alpha”. Isolate 3 was the most virulent, followed by isolate 4 , while the least pathogenic was isolate 5. Potato Dextrose medium was the best medium for linear and amount of growth for all tested isolates, whereas rate of growth varied between the different tested isolates with the different tested media. Optimum temperature for the fungal linear growth was 27°C, followed by 28°C, while the best amount of growth was obtained at 25°C for all tested isolates. Cucumber genotypes were susceptible to Fusarium oxysporum f.sp. cucumerinum and differed significantly in their susceptibility. The most tolerant cucumber genotype was “Zeina” as well as it recorded the highest survival plants. DNA analysis detected 33 loci with an average 4.125 loci/isolate. The highest number of polymorphic loci was 6 loci in both Fus 1&4 isolates, while the lowest was 1 loci in Fus 6 only. UPGMA cluster analysis divide into two sub clusters, one of them included Fus 6 only and the second include the rest seven isolates with different similarity values. 100 & 614 bp were detected in both highly pathogenic isolates and it could be carrying the genetic information affecting pathogenicity of Fusarium to cucumber plants. Grouping of Trichoderma isolates in UPGMA cluster analysis and variation in DNA profiles among isolates was not related to their biocontrol ability. Biocontrol agents great affected Fusarium growth in dual cultures and reduced it under laboratory conditions. Biocontrol agents minimized the disease parameters in comparing with infested control treatments by the most aggressive isolate under greenhouse condition.

Evaluation and Characterization of Some Egyptian Fusarium oxysporum Isolates for their Virulence on Tomato and PCR Detection of (SIX) Effector Genes

The genus Fusarium is comprises of different species which are furtherer divided into small groups called formae speciales according to their host specificity. It is remarkable that while an isolate belonging to particular formae speciales is considered highly pathogenic in a certain plant species, the many other isolates belonging to the same formae speciales may have no harm effect or even a beneficial relation to the same host plant. Traditionally, bioassays conducted under green house conditions were used to distinguish pathogenic and non-pathogenic isolates. However, such these techniques have some limitations due to the time consuming and the inconsistency of obtained results. In contrary, molecular identification techniques are candidate to play an important role in the characterization process of Fusarium isolates as well as with many other organisms. Recently, the ability of a Fusarium isolate to infect particular plant species was found to be dependent on specific genes encoding host determining ‘virulence factors’ that distinguish virulent from avirulent strains. More recently, eight fungal proteins were identified from xylem sap of infected plants, encompassing the small secreted proteins called Six1, Six2, Six3, Six4, Six5, Six6, Six7 and SIX 8. In the present study, the linkage between virulence potential of fifteen pathogenic isolates in addition to one non-pathogenic isolate, Fo162 , of Fusarium oxysporum and the presence of secreted in xylem effector genes (SIX) was determined. The results showed that the tested isolates were varied regarding to their pathogenicity potential toward tomato plants under greenhouse conditions. On the other hand, the amplicons of SIX1, SIX5 and SIX 7 were detected with most hyper virulent isolates while no amplicons for any tested SIX genes were observed with the non-pathogenic isolate (Fo162) as well as with the most hypo virulent isolates. These results, suggested that SIX1, SIX5 and SIX6 may play a distinct role in virulence potential of these Fusarium oxysporum isolates toward tomato plants under Egyptian conditions.

Role of Fusaric Acid Mycotoxin in Pathogensis Process of Tomato Wilt Disease Caused by Fusarium oxysporum

Different Fusarium oxysporum isolates were tested under greenhouse conditions to determine their virulence potential toward tomato plants. Severity and development of Fusarium wilt disease was recorded 4, 6 and 8 weeks after pathogen inoculation. Chromatogram assay was conducted using HPLC to evaluate the capability of the tested isolates to produce Fusaric acid and to investigate the possible correlation between FA accumulation and Fusarium wilt disease development on tomato plants. The results showed that all tested isolates were pathogenic and varied significantly with regard to their virulence potential on tomato under the test conditions. The results showed also that all tested isolates were able to produce FA. Moreover, remarkable variation in FA accumulation was observed among the tested isolates at 4, 6 and 8 weeks post inoculation with the individual isolates. Four weeks post inoculation; the recorded data indicated that no clear correlation could be detected between FA accumulation and virulence of the tested isolates. In contrary, FA accumulation was in positive proportional relationship with virulence of the tested Fusarium isolates at 6 weeks post inoculation. Furthermore, differences in production of total secondary metabolites were observed within Fusarium isolates under in vitro conditions. These results revealed that FA could be play an important role in the development of Fusarium wilt disease at middle and last stages of tomato growth, while, it seems that no distinctive role of FA in the first stages of pathogenesis process of the tested Fusarium oxysporum isolates.

The application of Arabidopsis thaliana in studying tripartite interactions among plants, beneficial fungal endophytes and biotrophic plant-parasitic nematodes

The research demonstrated that Arabidopsis can be used as a model system for studying plant-nematode-endophyte tripartite interactions; thus, opening new possibilities for further characterizing the molecular mechanisms behind these interactions. Arabidopsis has been established as an important model system for studying plant biology and plant-microbe interactions. We show that this plant can also be used for studying the tripartite interactions among plants, the root-knot nematode Meloidogyne incognita and a beneficial endophytic isolate of Fusarium oxysporum, strain Fo162. In various plant species, Fo162 can systemically reduce M. incognita infection development and fecundity. Here it is shown that Fo162 can also colonize A. thaliana roots without causing disease symptoms, thus behaving as a typical endophyte. As observed for other plants, this endophyte could not migrate from the roots into the shoots and leaves. Direct inoculation of the leaves also did not result in colonization of the plant. A significant increase in plant fresh weight, root length and average root diameter was observed, suggesting the promotion of plant growth by the endophyte. The inoculation of A. thaliana with F. oxysporum strain Fo162 also resulted in a significant reduction in the number of M. incognita juveniles infecting the roots and ultimately the number of galls produced. This was also observed in a split-root experiment, in which the endophyte and nematode were spatially separated. The usefulness of Arabidopsis opens new possibilities for further dissecting complex tripartite interactions at the molecular and biochemical level.

BOX-PCR- and ERIC-PCR-based genotyping and phylogenetic correlation among Fusarium oxysporum isolates associated with wilt disease in Psidium guajava L.

Abstract Fusarium oxysporum f. sp. psidii is a soilborne fungal pathogen that causes wilt disease in guava. There is an urgent need to establish a sensitive and specific molecular assay to diagnose the disease. A genetic fingerprint of the guava wilt pathogen also needs to be established. We isolated and identified 21 isolates of F. oxysporum f. sp. psidii from soil and infected roots of wilted guava, from different agro-climatic regions of India. We used BOX-PCR and enterobacterial repetitive intergenic consensus (ERIC)-PCR for generating a genetic fingerprint of F. oxysporum f. sp. psidii that ranged from 150 to 2500 bp in size. A dendrogram was constructed for the isolates on the basis of both the fingerprint patterns and the highest and lowest similarity values. The latter were observed for Fop123–Fop127 (at 94.0%) and Fop18–Fop24 (at 18.0%), respectively. Molecular data were derived from an analysis of the internal transcribed spacer sequences of 38 isolates belonging to 19 taxa within the species F. oxysporum. In this study, F. oxysporum f. sp. psidii was grouped in a single cluster that represented a different genetic structure. This study suggests that BOX-PCR and ERIC-PCR could be suitable, rapid, reproducible, and useful techniques for the discrimination of F. oxysporum f. sp. psidii, to better manage guava wilt disease.

Genetic diversity and virulence of Italian strains of Fusarium oxysporum isolated from Eustoma grandiflorum

Twenty-seven isolates of Fusarium oxysporum f. sp. eustomae obtained from diseased Eustoma grandiflorum (lisianthus) plants in north Italy, showing typical fusarium wilt symptoms, were studied for genetic diversity, pathogenicity, and vegetative compatibility (VC). The strains were examined for differences in the nucleotide sequence of translation elongation factor 1-α (tef) and two endopolygalacturonase genes (pg1 and pg5). The phylogenetic analysis performed on the isolates enabled the identification of three main groups, named I, II, and III, and two subgroups (Ia and Ib). In pg1 and pg5 sequences, most of nucleotide variations resulted in aminoacid variations, while in tef most of SNPs are in the introns or are silent. By considering the virulence of the strains included in Group I, a low virulence could be observed, Group II and III showed a reduced virulence at 30 °C compared to 20 °C. Some cultivars showed higher tolerance at 30 °C. Principal component analysis (PCA) performed on pathogenicity values, confirmed the three molecular clusters. VC identified two VCGs (vegetative compatibility groups) in Group II, one VCG in Group III, and vegetatively incompatible isolates grouped together in Group I. The integrated analysis confirmed the presence of virulence variation and genetic diversity among the F. oxysporum f. sp. eustomae isolates studied.

Pathogenicity and genetic diversity of Fusarium oxysporum isolates from corms of Crocus sativus

Crocus sativus is a triploid sterile plant and autumnal flowering geophyte with corms. As a subterranean organ, the corm is susceptible to diseases caused by fungi, bacteria, nematodes and viruses. Fusarium corm rot incited by F. oxysporum is the most destructive disease in saffron, having caused severe yield losses in saffron producer's countries. Infected plants die off early, resulting in reduction of corm yield, quality and flower and stigma production. Little is known about the formae speciales attacking saffron and less about the relationship among the fungus and the possible hosts. In this study we investigate the formae speciales which colonize saffron and their relationship with some members of iridaceae such as C. vernus (ornamental crocus), gladiolus and narcissus using pathogenicity tests; we determine whether different pathogenic isolates of F. oxysporum can be distinguished by ISSR, and we analyze the genetic relationships and variability among some isolates of these pathogens. We found two formae speciales iridiacearum and croci which attack different iridaceous crops and Crocus sp., respectively and we suggested the creation of a new formae speciales saffrani which shows only pathogenicity on saffron corms. From ISSR analysis, the unweighted paired group method with arithmetic averages cluster analysis (UPGMA) was used to discriminate the F. oxysporum isolates, we were able to differentiate among f. sp. from saffron corms and other formae speciales of F. oxysporum but not among formae speciales iridiacearum, croci and saffrani. Furthermore, we searched for fum1, tri5, tri7 and tri13 genes using PCR assays, however, all the isolates from saffron corms were negative.