Isolates Of Fusarium Oxysporum Research Articles

Presence of putative pathogenicity genes in isolates of Fusarium oxysporum f. sp. cubense from Australia

Fusarium oxysporum f. sp. cubense (Foc), causal agent of Fusarium wilt of banana, is among the most destructive pathogens of banana and plantain. Understanding pathogenicity in Foc is of key importance to disease management, yet its genetic basis is poorly understood. Recent research with F. oxysporum f. sp. lycopersici (Fol), causal agent of Fusarium wilt of tomato, has elucidated the role of SIX-genes (secreted in xylem) in pathogenicity in the Fol-tomato pathosystem. Using hybridisation analysis and PCR, we detected homologues of three SIX-genes, SIX1, SIX7 and SIX8, in isolates of Foc from Australia and sequenced these putative Foc pathogenicity genes.

Detection ofFusarium oxysporumFungal Isolates Using ATR Spectroscopy

Fungi are considered as serious pathogens for many plants, potentially causing severe economic damage. Early detection and identification of these pathogens is crucial for their timely control. The methods available for identification of fungi are time consuming and not always very specific. In this study, the potential of FTIR-ATR spectroscopy was examined together with advanced mathematical principle component analysis (PCA) and statistical linear discriminant analysis (LDA) to differentiate among 10 isolates of Fusarium oxysporum. The results are encouraging and indicate that FTIR-ATR can successfully detect different isolates of Fusarium oxysporum. Based on PCA and LDA calculations in the region 850–1775 cm-1with 16 PC's, the different strains from the same fungal genus could be classified with 75.3% and 69.5% success rates using the “leave one out” method and “20–80% algorithm” respectively.

Identification of fungal phytopathogens using Fourier transform infrared-attenuated total reflection spectroscopy and advanced statistical methods

The early diagnosis of phytopathogens is of a great importance; it could save large economical losses due to crops damaged by fungal diseases, and prevent unnecessary soil fumigation or the use of fungicides and bactericides and thus prevent considerable environmental pollution. In this study, 18 isolates of three different fungi genera were investigated; six isolates of Colletotrichum coccodes, six isolates of Verticillium dahliae and six isolates of Fusarium oxysporum. Our main goal was to differentiate these fungi samples on the level of isolates, based on their infrared absorption spectra obtained using the Fourier transform infrared-attenuated total reflection (FTIR-ATR) sampling technique. Advanced statistical and mathematical methods: principal component analysis (PCA), linear discriminant analysis (LDA), and k-means were applied to the spectra after manipulation. Our results showed significant spectral differences between the various fungi genera examined. The use of k-means enabled classification between the genera with a 94.5% accuracy, whereas the use of PCA [3 principal components (PCs)] and LDA has achieved a 99.7% success rate. However, on the level of isolates, the best differentiation results were obtained using PCA (9 PCs) and LDA for the lower wavenumber region (800-1775 cm(-1)), with identification success rates of 87%, 85.5%, and 94.5% for Colletotrichum, Fusarium, and Verticillium strains, respectively.

Screening of Resistant Varieties and Antagonistic Fusarium oxysporum for Biocontrol of Fusarium Wilt of Chilli

Chilli is an important vegetable/spice, and its socio-cultural role is remarkable worldwide. The enormous popularity and demand for chilli is providing a boost to the chilli industry, but its production is increasingly constrained by diseases. Chilli producers have reported Fusarium wilt, as the frequently encountered disease. The present investigation focuses on biological control, which is found effective to manage this disease. A survey was conducted at Uttarakhand and Uttar Pradesh states in India, for collection of soil and plant samples. A total of eighty isolates of Fusarium were isolated from these samples. Among these, forty eight isolates of Fusarium oxysporum were identified on the basis of morphological and molecular characteristics, using speciesspecific primers. Pathogenicity test on chilli was conducted. One isolate of F. oxysporum was found most virulent pathogen, while eleven isolates were non- pathogenic isolates. Isolate no. 65 was found most antagonistic towards F. oxysporum, under in-vitro dual culture assay. Thirty chilli varieties were screened for evaluation of resistance. Among these, two varieties were found resistant against the Fusarium wilt. The present investigation focused on recovery of antagonistic Fusarium and resistant varieties of chilli, for controlling and resisting wilt and improving the soil health.

Genetic diversity and pathogenicity of Fusarium oxysporum isolated from wilted rocket plants in Italy

Thirty-six isolates of Fusarium oxysporum originated from Eruca vesicaria and Diplotaxis tenuifolia together with eight reference strains belonging to the formae speciales raphani, matthioli and conglutinans, typical on the Brassicaceae family, were tested for pathogenicity on two species of rocket plants (E. vesicaria L., syn. E. sativa, cv. ‘Rucola coltivata’; and D. tenuifolia cv. ‘Winter’) cultivated in the glasshouse. The results showed that different isolates were slightly, moderately or highly virulent. The strains were examined for differences in the nucleotide sequence of the ribosomal DNA (rDNA) intergenic spacer (IGS) region, about 2.5 kb long. The phylogenetic (neighbor-joining) analysis performed on the isolates enabled identification of four different groups, named I, II, III and IV. Thirty-one isolates out of 36 clustered in group I and were genetically similar to F. oxysporum f.sp. raphani. By considering the pathogenicity of the strains included in Group I, a partial host specialization could be observed: the average disease index of the isolates from D. tenuifolia was higher on wild rocket, whereas the average disease index of the isolates from E. vesicaria was higher on cultivated rocket. Moreover, isolates from cultivated rocket showed, on average, a higher degree of aggressiveness than the isolates from wild rocket. Concerning Group I, the sequence analysis confirmed the homogeneity of the population, with only five parsimony-informative SNPs and five haplotypes. Twenty-six out of 31 isolates belonged to haplotype 1. Groups II and III were genetically similar to strains of F. oxysporum f.sp. matthioli. Three other strains, not pathogenic or with a medium level of virulence, clustered together in Group 4, but their sequence was distant from that of other formae speciales. The pathogenicity and IGS analysis confirmed the presence of virulence variation and genetic diversity among the F. oxysporum isolates studied. To our knowledge, this is the first report of differentiation of formae speciales of F. oxysporum on rocket plants by IGS analysis.

Genetic diversity of Fusarium oxysporum and related species pathogenic on tomato in Algeria and other Mediterranean countries

In order to characterize the pathogen(s) responsible for the outbreak of fusarium diseases in Algeria, 48 Fusarium spp. isolates were collected from diseased tomato in Algeria and compared with 58 isolates of Fusarium oxysporum originating from seven other Mediterranean countries and 24 reference strains. Partial sequences of the translation elongation factor EF‐1α gene enabled identification of 27 isolates as F. oxysporum, 18 as F. commune and three as F. redolens among the Algerian isolates. Pathogenicity tests confirmed that all isolates were pathogenic on tomato, with disease incidence greater at 28°C than at 24°C. All isolates were characterized using intergenic spacer (IGS) DNA typing, vegetative compatibility group (VCG) and PCR detection of the SIX1 (secreted in xylem 1) gene specific to F. oxysporum f. sp. lycopersici (FOL). No DNA polymorphisms were detected in the isolates of F. redolens or F. commune. In contrast, the 27 Algerian isolates of F. oxysporum were shown to comprise nine IGS types and 13 VCGs, including several potentially new VCGs. As none of the isolates was scored as SIX1+, the 27 isolates could be assigned to F. oxysporum f. sp. radicis‐lycopersici (FORL). Isolates from Tunisia were also highly diverse but genetically distinct from the Algerian isolates. Several Tunisian isolates were identified as FOL by a PCR that detected the presence of SIX1. The results show that isolates from European countries were less diverse than those from Tunisia. Given the difference between Algerian populations and populations in other Mediterranean countries, newly emergent pathogenic forms could have evolved from local non‐pathogenic populations in Algeria.

Genetic Diversity of Fusarium oxysporum f.sp. cubense Isolates (Foc) of India by Inter Simple Sequence Repeats (ISSR) Analysis

To find out the genetic diversity of Indian Foc isolates of banana, a total of 107 isolates of Fusarium which includes 98 Foc isolates obtained from different banana growing regions of India and seven Foc isolates belong to all known VCGs obtained from Australia and two non-pathogenic Fusarium oxysporum (npFo) isolates were subjected to ISSR analysis. In the initial screening of ISSR primers, out of 34, 10 primers which generated more polymorphic bands were selected for further analysis. The Phylogenetic analysis carried out based on the fingerprints obtained through ISSR analysis indicated the presence of wide genetic diversity among the Foc isolates of India and also its polyphyletic nature. Totally, seven different clusters were obtained and these clusters differentiated the Foc isolates of India based on the races/VCGs. Besides, the cluster analysis clearly distinguished the freshly emerged Foc strain obtained from cv. Grand Naine (Cavendish-AAA) and Poovan (Mysore-AAB) from the other Foc isolates. The non-pathogenic F. oxysporum isolates which have been included for comparison purpose also clustered separately. All these above said findings indicates for the first time the discriminatory power of ISSR to clearly distinguish and separate the Foc isolates according to its race/VCGs and also its virulence. This study would be useful not only to design and develop effective management strategies but also useful for quarantine purposes.

Molecular diversity in Indian isolates of Fusarium oxysporum f.sp. lentis inciting wilt disease in lentil (Lens culinaris Medik)

For integrated management of wilt disease, foolproof knowledge about the genetic diversity among the prevalent isolates is very important. One hundred (100) isolates of Fusarium oxysporum f. sp. lentis, causing agent of vascular wilt in lentil were collected from different agro-climatic regions of India. Finally, fifteen distinct F. oxysporum f. sp. lentis isolates were selected for molecular characterization by three molecular markers. Twenty randomly amplified polymorphic DNA (RAPD)primers produced a total of 105 reproducible bands, out of which 81 (77.14%) were polymorphic and 24 (22.85%) were monomorphic. Nine simple sequence repeats (SSR) primer pairs amplified 21 alleles with 2.33 alleles per primer. Considerable length variations (561 to 668 bp) in rDNA regions were found and restriction digestion of amplified rDNA region produced forty eight different DNA bands. Three molecular markers revealed varying degree of genetic diversity in the selected isolates ranging from 54% in case of RAPD to up to 35% with ITS markers. Based on the coefficient of similarity, the isolates grouped into two major clusters in the dendrogram. Isolates from North Indian regions grouped in same cluster, whereas isolates from north east regions and eastern region fell in another cluster. This information will be helpful for pathologists and plant breeders to design effective resistance breeding programs in lentil taking into account the diversity in wilt pathogen. Key words: Indian isolates, Fusarium oxysporum f.sp. lentis, vascular wilt, molecular diversity.

Isolation of differentially expressed genes during interactions between tomato cells and a protective or a non-protective strain of Fusarium oxysporum

Pathogenic isolates of Fusarium oxysporum applied on a non-host plant species, as soil-borne non-pathogenic isolates, are able to protect this plant against pathogenic strains inducing wilts. Several modes of action contribute to the biocontrol activity of these protective strains; however the genetic basis of the biocontrol mechanisms is far from being understood. The aim of this study was to identify genes involved in biocontrol activity of F. oxysporum using an original model made of Fom24, a strain protective on tomato and its mutant rev157 which has lost its protective capacity. A Rapid Subtractive Hybridization (RaSH) approach was chosen to identify genes up-regulated in the protective or in the non-protective interaction when germinated conidia of either Fom24 or rev157 are confronted to tomato cell cultures. A total of 86 up-regulated sequences were generated, 42 and 44 from the protective and the non-protective interaction respectively. Homology searches led to identification of both plant and fungal genes that were grouped according to their putative functions. Among plant genes, those involved in plant response to stresses were the most abundant. Expression profiles of genes homolog to a basic endochitinase, a ferredoxine-NADP(H) reductase (FNR), an ATP synthase and the RPM1-interacting protein 4 (RIN4) were confirmed by Northern blotting. A large proportion of fungal sequences were encoding genes of unknown function; among other, those involved in response to oxidative stress and a gene putatively encoding an enolase are the most promising to further study their potential role in the protective interaction between F. oxysporum and tomato.

VEGETATIVE COMPATIBILITY GROUP ANALYSIS OF INDONESIAN FUSARIUM OXYSPORUM F. SP. CUBENSE ISOLATES

As part of an Australian Centre for International Agricultural Research (ACIAR)-funded project, vegetative compatibility group (VCG) analysis was used to characterise isolates of Fusarium oxysporum f. sp. cubense (Foc) collected from 12 Indonesian provinces. Samples were taken almost exclusively from cultivated bananas (around 20 different cultivars) in smallholder and backyard plots. In total, 178 isolates were received and, of these, 135 have been assigned a VCG. Isolates have tested positive for the following VCGs or VCG complexes: 0120/15, 0121, 0123, 0124/5, 0126, 01213/16, 01218 and 01219. VCG 01213/16 (the so-called tropical race 4, TR4) was by far the most prevalent strain detected, accounting for approximately 60% of the positive results. It was most commonly isolated from the cultivars 'Barangan' (syn. 'Lakatan', AAA) and 'Pisang Raja' (AAB) and was detected in Sumatra (Aceh and West Sumatra), Java (West Java and Yogyakarta), Kalimantan (West and East Kalimantan), Sulawesi (South East and North Sulawesi) and Papua. These findings highlight the wide distribution of Foc TR4 in Indonesia and the importance of managing its spread. © International Society for Horticultural Science (ISHS)

Direct effect of biocontrol agents on wilt and root-rot diseases of sesame

In Egypt, sesame cultivation is subject to attack by wilt and root-rot diseases caused by Fusarium oxysporum f.sp. sesami (Zap) Cast. and Macrophomina phaseolina (Maubl) Ashby causing losses in quality and quantity of sesame seed yield. Bacillus subtilis and Trichoderma viride isolates which were isolated from sesame rhizosphere were the most effective to antagonise fungal pathogens, causing high reduction of hyphal fungal growth. Trichoderma viride was found to be mycoparasitic on Fusarium oxysporum f.sp. sesami and M. phaseolina causing morphological atternation of fungal cells and sclerotial formation. In general, Bacillus subtilis, T. viride, avirulent Fusarium oxysporum isolate and Glomus spp. (Amycorrhizae) significantly reduced wilt and root-rot incidence of sesame plants at artificially infested potted soil by each one or two pathogens. Data obtained indicate that Glomus spp significantly reduced wilt and disease severity development on sesame plants followed by T. viride. Meanwhile, avirulent Fusarium oxysporum isolate followed by Glomus spp. were effective against root-rot disease incidence caused by M. phaseolina. Glomus spp. followed by B. subtilis significantly reduced wilt and root-rot disease of sesame plants. All biotic agents significantly reduced F. oxysporum f.sp. sesami and M. phaseolina counts in sesame rhizosphere at the lowest level. Glomus spp. and the avirulent isolate of F. oxysporum eliminated M. phaseolina in sesame rhizosphere. Meanwhile T. viride was the best agent at reducing F. oxysporum at a lower level than other treatments. Application of VA mycorrhizae (Glomus spp.) in fields naturally infested by pathogens significantly reduced wilt and root-rot incidence and it significantly colonised sesame root systems and rhizospheres compared to untreated sesame transplantings.

Inhibitory and stimulatory effects of essential oils and individual monoterpenoids on growth and sporulation of four soil-borne fungal isolates of Aspergillus terreus, Fusarium oxysporum, Penicillium expansum, and Verticillium dahliae

The effect of essential oils and individual monoterpenoids on soil-borne fungi, in pure and mixed cultures, in growth media and in the soil environment, was investigated. Essential oils were extracted from lavender (Lavandula stoechas), oregano (Origanum vulgare subsp. hirtum), sage (Salvia fruticosa) and spearmint (Mentha spicata). The monoterpenoids tested were fenchone, carvacrol, 1,8-cineole, carvone, α-pinene and terpinen-4-ol. Their effect was examined on growth and sporulation of Aspergillus terreus, Fusarium oxysporum, Penicillium expansum and Verticillium dahliae isolated from an organic cultivation of tomato. All tested essential oils and individual monoterpenoids inhibited mycelial growth in all fungi and conidial production in most fungi. The strongest inhibitory activity on mycelial growth was exhibited by oregano and spearmint oils and by carvacrol and carvone, respectively their main constituents. The inhibitory activity was clearly fungistatic in A. terreus and F. oxysporum but fungicidal in V. dahliae. On sporulation, clearly stimulatory effects were observed alongside inhibitory ones. Conidial production was always promoted by α-pinene in P. expansum and by sage oil in F. oxysporum. At certain dosages it was promoted by cineole and carvone in F. oxysporum, and by lavender oil in A. terreus and V. dahliae. Experiments with carvone and carvacrol against mixed fungal cultures in a soil environment showed that V. dahliae was the most sensitive and A. terreus the most tolerant of the four fungi. Our results demonstrate strong but divergent effects and selectivity of action of the lower terpenoids on fungal strains that can become serious pests of tomato. Of special importance is the complete inhibition of growth and conidial production of V. dahliae, a pathogen otherwise very resistant to chemical control.

Prevalence of Deg Nala disease in eastern India and its reproduction in buffaloes by feeding Fusarium oxysporum infested rice straw

Objective To undertake a study on prevalence of Deg Nala disease in eastern states of India and to reproduce the disease in buffaloes by the Fusarium spp., isolated from the affected region. Methods During this investigation, a survey was conducted covering four states of eastern region to identify the Deg Nala cases as well as to isolate and characterize the causative agent(s). An experimental study was carried out to reproduce the disease in healthy male buffaloes (2–3 years age) by randomly dividing them into five groups (four in each group). Each individual group was fed with rice straw artificially infested with either of the two representative isolates of Fusarium oxysporum (F. oxysporum) (F01, F02) or representative reference strains of Fusarium equiseti (F. equiseti) (ITCCF-2470) and Fusarium moniliforme (F. moniliforme) (ITCCF-4821) for 30 days, whereas the control group was fed with normal rice straw only. Results A total of 658 Deg Nala cases were recorded and 12 Fusarium isolates were identified from the mouldy rice straw collected from these affected areas. The characterization of the isolates revealed three species viz., F. oxysporum, F. equiseti and F. moniliforme, among which F. oxysporum was predominant. The disease was artificially reproduced in three buffaloes in F01 group and one in F02 group within 20–23 days by feeding F. oxysporum infested rice straw which resembled the clinical symptoms and gross lesions of natural Deg Nala cases. Conclusions The field investigation and laboratory studies, including experimental production of Deg Nala disease suggest the possible involvement of mycotoxins. However, further investigations needs to be done to understand nature of the toxic factors involved in production of the Deg Nala disease.

Stable integration and expression of a plant defensin in tomato confers resistance to fusarium wilt

Plant defensins are small cysteine-rich peptides which belong to a group of pathogenasis related defense mechanism proteins. The proteins inhibit the growth of a broad range of microbes and are highly stable under extreme environmental stresses. Tomato cultivation is affected by fungal disease such as Fusarium wilt. In order to overcome fungal damages, transgenic tomato plants expressing the Medicago sativa defensin gene MsDef1 under the control of the CaMV 35S promoter were developed. The Fusarium-susceptible tomato (Lycobersicum esculentum Mill) cultivar CastleRock was used for transformation to acquire fungal resistance. Hypocotyl with a part of cotyledon (hypocotyledonary) for young tomato seedlings were used as an explant material and transformation was performed using the biolistic delivery system. Bombarded shoots were selected on regeneration medium supplemented with hygromycin and suitable concentrations of BA, zeatin ripozide and AgNO3. Putative transgenic plantlets of T0 were confirmed by PCR analysis using primers specific for the transgene and the transformation frequency obtained was 52.3%. Transformation and transcription of transgenes were confirmed in T1 by PCR, Southern hybridizations, and reverse-transcription PCR (RT-PCR). The copy numbers of integrated transgene into tomato genome ranged between 1-3 copies. Greenhouse bioassay was performed on the transgenic T1 and T2 young seedlings and non-transgenic controls by challenging with a vigorous isolate of the fungal pathogen Fusarium oxysporum f. sp. Lycopersici. The level of fungal infectivity was determined using RT-PCR with tomatinase specific primers. Transgenic lines were more resistant to infection by fusarium than the control plants. These results indicated that overexpressing defensins in transgenic plants confer resistance to fungal pathogens.

ITS-RFLP fingerprinting and molecular marker for detection of Fusarium oxysporum f.sp. ciceris

Genetic diversity of 11 representative isolates of Fusarium oxysporum f.sp. ciceris causing chickpea wilt was determined through internal transcribed spacer (ITS) region of the ribosomal DNA-restriction fragment length polymorphism (ITS-RFLP). ITS1+5.8s+ITS2 regions of the isolates were amplified with a set of primers ITS1 and ITS4 and amplified products were digested with 4 restriction enzymes (AluI, MboI, RsaI, MseI). Six different kinds of ITS-RFLP patterns were obtained. The ITS region of these isolates was sequenced and deposited to NCBI GeneBank. The nucleotide sequence homology of ITS region grouped the isolates into 5 categories. Primers were designed with sequence information using Primer 3 software. F. oxysporum f.sp. ciceris specific markers (FOC F2 and FOC R2) based on ITS region were developed for the first time for detection of the pathogen. The markers produced an amplicon of 292 bp; they were validated against the isolates of the pathogen collected from different locations of India.

Fusarium oxysporum degradation and detoxification of a new textile-glycoconjugate azo dye (GAD)

Degradation and detoxification of textile dyes are of interest due to the huge environmental impact of such chemicals. An isolate of Fusarium oxysporum was used to degrade and to detoxify a new chemical class of textile dyes called Glycoconjugate Azo Dye (GAD). After 6d of growth in a liquid batch culture, the fungus degraded the dye and the culture medium at the end of incubation period showed a ˜100% detoxification compared to the initial dye solution. Increasing the initial fungal inoculum, the dye was totally decolourized after 24h of incubation. The degradation ability was found to be common among various isolates of F. oxysporum suggesting this as a specific trait of this species. Degrading rate was enhanced in concomitancy to the glucose depletion and the beginning of the stationary phase of growth, suggesting that the shift from the primary to the secondary metabolism may be the trigger of the degradation pathway. The Daphnia magna acute toxicity test demonstrated a strong detoxification of GAD-4 by F. oxysporum, resulting in non-toxic metabolite production. Fusarium oxysporum could, therefore, be taken into consideration to develop new remediation strategies of textile effluents.

Characterization of Fusarium oxysporum f.sp. cepae from Onion in Turkey Based on Vegetative Compatibility and rDNA RFLP Analysis

Seventy-five isolates of Fusarium oxysporum f.sp. cepae, the causal agent of basal plate rot on onion, were obtained from seven provinces of Turkey. The isolates were characterized by vegetative compatibility grouping (VCGs) and restriction fragment length polymorphism (RFLP) analysis of the nuclear ribosomal DNA intergenic spacer region (IGS). Forty-eight vegetative compatibility groups were found, each containing a single isolate. Only one isolate formed strong heterokaryons with the reference isolates of VCG 0423. Five isolates were heterokaryon self-incompatible. Restriction fragment analysis with six different enzymes revealed 13 IGS types among 75 F. oxysporum isolates from Turkey as well as 16 reference isolates from Colorado, USA. The majority of single-member VCGs produced identical RFLP banding patterns with minor deviations, considerably different from those of the reference VCG isolates. These results suggested that isolates of F. oxysporum f.sp. cepae in Turkey derived from distinct clonal lineages and mutations at one or more vegetative compatibility loci restrict heterokaryon formation.

Stimulation of mycelial growth of pathogenic and seabed isolates of Fusarium oxysporum in presence of salts

The mycelial growth of eleven Fusarium oxysporum strains, eight isolated from seabed soil of the South-eastern Mediterranean coast of Spain and three formae speciales from diseased plants were tested on potato-dextrose-agar adjusted to different osmotic pressures with either KCl or NaCl (-1.50 to -144.54 bar) at 10°C intervals ranging from 15 to 35°C. The extent of growth of F. oxysporum shows the same pattern for isolates from the seabeds that for isolates of Formae speciales. Maximal growth was observed at -13.79 bar of osmotic pressure at 25°C with an acute decrease at -41.79 bar and lower. At 35°C maximal growth was observed at -41.79 bar of osmotic pressure not only for seabeds isolates but also for pathogenic F. speciales isolates. These findings could indicate that F. oxysporum is well adapted to exist in moderate saline habitats. It does not seem that the pathogenicity of the isolates is a factor that determines the response to the salinity, but that behavior seems to be common to all the isolates studied and it could be speculated to be a specific behavior.

Identification of genetic variability among isolates of Fusarium oxysporum f. sp. vasinfectum of cotton

Fusarium wilt of cotton caused by Fusarium oxysporum f.sp. vasinfectum (FOV) causes yield losses, especially in the States of Sao Paulo and Parana. The disease can mainly be controlled by the use of resistant cultivars, and knowledge regarding the genetic diversity among isolates of the pathogen has become essential. Diversity among 15 isolates collected from different Brazilian cotton-producing States was studied along with one isolate of F. solani, using molecular techniques. The results of RAPD, PCR-RFLP of rDNA, ERIC and REP-PCR were comparable with each other and indicated the existence of genetic variability among some of the FOV isolates of different geographic origins. This indicates the necessity of using different FOV isolates that represent the genetic diversity of the population, while screening cultivars for genetic resistance against this disease, so that only cultivars that are resistant to isolates from different geographic origins may be used in breeding programs.

Genetic Variability Analysis and Molecular Detection of Fusarium oxysporum f.sp. eustomae Isolated from Eustoma grandiflorum in Northern Italy

AbstractA total of 35 isolates of Fusarium oxysporum f.sp. eustomae obtained from diseased Eustoma grandiflorum plants in northern Italy, showing typical Fusarium wilt symptoms, were analysed for their genetic variability and molecular identification. Genetic diversity of the isolates was studied by using random amplified polymorphic DNA (RAPD). This analysis clustered the isolates into three groups at a genetic similarity of 69%. Sequence analysis of RAPD fragments led to the design of a pair of specific primers that amplify a 505‐bp SCAR (sequence characterized amplified region) marker (SCAR505) which was used to rapidly detect F. oxysporum f.sp. eustomae on Eustoma grandiflorum plants. In a temperature‐controlled chamber, detection of the pathogen by PCR was 100% successful in root and stem samples of infected but still symptomless plants. The diagnostic procedure could be completed in 1 day and allowed rapid and reliable detection of the pathogen in asymptomatic plants in the early stages of disease development.