Real-time PCR for differential determination of the tomato wilt fungus, <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">lycopersici</Emphasis>, and its races

Five primer/probe sets to identify the tomato wilt pathogen, Fusarium oxysporum f. sp. lycopersici (FOL), and its three races selectively were designed based on the rDNA-intergenic spacer and avirulence genes. Real-time PCR using genomic DNA from mycelia and soil DNA with the primer/probe sets allowed the successful identification of FOL and its races.     

Detection of Fusarium oxysporum f. sp. dianthi in Carnation Tissue by PCR Amplification of Transposon Insertions

ABSTRACT Strains of the carnation wilt pathogen, Fusarium oxysporum f. sp. dianthi, can be distinguished by DNA fingerprint patterns, using the fungal transposable elements Fot1 and impala as probes for Southern hybridization. The DNA fingerprints correspond to three groups of F. oxysporum f. sp. dianthi strains: the first group includes isolates of races 1 and 8; the second group includes isolates of races 2, 5 and 6; and the third group includes isolates of race 4. Genomic DNAs flanking race-associated insertion sites of Fot1 (from races 1, 2, and 8) or impala (from race 4) were amplified by the inverse polymerase chain reaction (PCR) technique. These regions were cloned and sequenced, and three sets of primers overlapping the 3' or 5' end of the transposon and its genomic insertion were designed. Using fungal genomic DNA as template in PCR experiments, primer pairs generated amplification products of 295, 564 and 1,315 bp, corresponding to races 1 and 8; races 2, 5, and 6; and race 4, respectively. When multiplex PCR was performed with genomic DNA belonging to races 1 and 8, 2, or 4, single amplimers were generated, allowing clear race determination of the isolate tested. PCR was successfully performed on DNA extracted from susceptible carnation cv. Indios infected with isolates representative of races 1, 2, 4, and 8.     

浙江省铁皮石斛根腐病病原真菌的鉴定

为明确铁皮石斛根腐病病原真菌,于其主产地浙江省金华市武义县收集铁皮石斛根腐病病株,采用平板分离方法对病原真菌进行分离,使用镰刀菌种特异性引物并结合ITS和TEF序列分析及形态学鉴定确定该镰刀菌的分类地位。结果表明,共分离纯获得真菌117株,其中有105株镰刀菌;经分子生物学分析及形态学鉴定结果显示,分离出的镰刀菌为层出镰刀菌Fusarium prolife‐mum、茄病镰刀菌F. solani、尖孢镰刀菌F. oxysporum和厚垣镰刀菌F. chlamydosporum四个种,其中层出镰刀菌在数量上具有优势地位,占总镰刀菌数的44.8%;茄病镰刀菌、尖孢镰刀菌、厚垣镰刀菌分别占总镰刀菌数的21.0%、15.2%和19.0%。在致病性测定中发现层出镰刀菌和茄病镰刀菌并不具备致病性,尖孢镰刀菌的致病性明显弱于厚垣镰刀菌,表明厚垣镰刀菌为浙江省金华市武义县铁皮石斛根腐病的主要致病菌。     

Specific Detection of Tomato Pathotype of Verticillium dahliae by PCR Assays

Verticillium dahliae Klebahn is the causal agent of tomato wilt disease. Isolates of V. dahliae can be classified based on pathogenicity to tomato, but the pathotypes are indistinguishable in morphology. We designed PCR primers for specific detection of isolates pathogenic to tomato (tomato pathotype) from the sequences of a pathotype-specific gene, vdt1. With the primer pair Tg5/Tc3, a PCR product (approximately 3.2 kb) specific to tomato pathotype was amplified from the genomic DNA of isolates. Using the primer pair, a tomato pathotype isolate was specifically detected from hypocotyls of inoculated tomato and eggplant. On the other hand, no amplification was observed from non-tomato pathotype isolates of V. dahliae, some other wilt pathogens of tomato and a healthy host plant. Therefore, the primer pair can be useful for pathotype-specific detection of V. dahliae as well as for diagnosis of wilt disease of tomato plant. Received 7 September 2001/ Accepted in revised form 3 December 2001     

Conventional PCR and real time quantitative PCR detection of <Emphasis Type="Italic">Phytophthora cryptogea</Emphasis> on <Emphasis Type="Italic">Gerbera jamesonii</Emphasis>

A conventional PCR and a SYBR Green real-time PCR assays for the detection and quantification of Phytophthora cryptogea, an economically important pathogen, have been developed and tested. A conventional primer set (Cryp1 and Cryp2) was designed from the Ypt1 gene of P. cryptogea. A 369 bp product was amplified on DNA from 17 isolates of P. cryptogea. No product was amplified on DNA from 34 other Phytophthora spp., water moulds, true fungi and bacteria. In addition, Cryp1/Cryp2 primers were successfully adapted to real-time PCR. The conventional PCR and real-time PCR assays were compared. The PCR was able to detect the pathogen on naturally infected gerbera plants and on symptomatic artificially infected plants collected 21 days after pathogen inoculation. The detection limit was 5 × 10³ P. cryptogea zoospores and 16 fg of DNA. Real-time PCR showed a detection limit 100 times lower (50 zoospores, 160 ag of DNA) and the possibility of detecting the pathogen in symptomless artificially infected plants and in the re-circulating nutrient solution of closed soilless cultivation systems.     

Development of a molecular marker for specific detection of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">cubense</Emphasis> race 4

Fusarium oxysporum f. sp. cubense is the causal agent of Panama disease of banana. A rapid and reliable diagnosis is the foundation of integrated disease management practices in commodity crops. For this diagnostic purpose, we have developed a reliable molecular method to detect Foc race 4 isolates in Taiwan. By PCR amplification, the primer set Foc-1/Foc-2 derived from the sequence of a random primer OP-A02 amplified fragment produced a 242 bp size DNA fragment which was specific to Foc race 4. With the optimized PCR parameters, the molecular method was sensitive and could detect small quantities of Foc DNA as low as 10 pg in 50 to 2,000 ng host genomic DNA with high efficiency. We also demonstrated that by using our PCR assay with Foc-1/Foc-2 primer set, Foc race 4 could be easily distinguished from other Foc races 1 and 2, and separated other formae speciales of F. oxysporum. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Fusarium Redolens f.sp asparagi, Causal Agent of Asparagus Root Rot, Crown Rot and Spear Rot

Two Fusarium species, F. oxysporum f.sp. asparagi and F. proliferatum, are known to be involved in the root and crown rot complex of asparagus. We have investigated reports on the involvement of F. redolens, a third species, which until recently was considered conspecific with F. oxysporum because of morphological similarities. RFLP analysis of the rDNA internal transcribed spacer region and AFLP fingerprinting identified eight strains from asparagus unambiguously as F. redolens. Four of these were tested and found to be pathogenic to asparagus either in this study (two strains) or in a previous one in which they were classified as F. oxysporum (three strains). Disease symptoms and disease development were the same as with F. oxysporum f.sp. asparagi and F. proliferatum. Present data and literature reports identify F. redolens as a host-specific pathogen involved in root, crown and spear rot of asparagus. The pathogen is formally classified as F. redolens Wollenw. f.sp. asparagi Baayen.     

A Phytophthora conserved transposon‐like DNA element as a potential target for soyabean root rot disease diagnosis

A transposon‐like element, A3aPro, with multiple copies in the Phytophthora sojae genome, was identified as a suitable detection target for this devastating soyabean root rot pathogen. The PCR primers TrapF1/TrapR1 were designed based on unique sequences derived from the transposon‐like sequence. A 267‐bp DNA fragment was amplified using this primer pair, the specificity of which was evaluated against 118 isolates of P. sojae, 72 isolates of 25 other Phytophthora spp., isolates of Pythium spp. and isolates of true fungi. In tests with P. sojae genomic DNA, detection sensitivities of 10 pg and 10 fg DNA were achieved in standard PCR (TrapF1/TrapR1) and nested PCR (TrapF1/TrapR1 and TrapF2/TrapR2), respectively. Meanwhile, PCR with TrapF1/TrapR1 primers detected the pathogen at the level of a single oospore, and even one zoospore. These primers also proved to be efficient in detecting pathogens from diseased soyabean tissues, residues and soils. In addition, real‐time quantitative PCR (qPCR) assays coupled with the TrapF1/TrapR1 primers were developed to detect and quantify the pathogen. The results demonstrated that the TrapF1/TrapR1 and TrapF2/TrapR2 primer‐based PCR assay provides a rapid and sensitive tool for the detection of P. sojae in plants and in production fields.     

Detection of <Emphasis Type="Italic">Agrobacterium vitis</Emphasis> by PCR using novel <Emphasis Type="Italic">virD2</Emphasis> gene-specific primers that discriminate two subgroups

Tumour tissue samples were collected from vines grown in various regions of Italy and other parts of Europe and extracted for detection of Agrobacterium vitis. Fifty strains were isolated on agar plates and screened by PCR with consensus primers from the virD2 gene. They were confirmed as A. vitis with a species-specific monoclonal antibody. The isolates were further analyzed by PCR for their opine synthase genes and ordered into octopine, nopaline and vitopine strains. Primers designed on the octopine synthase gene did not detect octopine strains of Agrobacterium tumefaciens. For quantitative PCR, virD2 fragments were sequenced: two classes of virD2 genes were found and two primer sets designed, which detected octopine and nopaline strains or only vitopine strains. For simultaneous identification of all opine-type strains, multiplex real-time PCR with either primer pair and SYBR Green was performed: the combined sets of primers gave signals with DNA from any A. vitis strain. Specificity of the new primers for real-time PCR was evaluated using several unidentified bacterial isolates from grapevines and other plant species. An elevated level of non-specific background was observed when the combined primer sets were used in multiplex PCR assays. The real-time PCR protocol was also used to detect A. vitis cells directly from grapevine tumours; avoiding direct isolation procedures a sensitivity in the range of one to ten cells per assay was found. Inhibition of the PCR reaction by plant material was overcome by treating tumour extracts with a DNA purification kit as a step for the isolation of nucleic acids.     

Cultural characteristics, pathogenicity and genetic diversity of Fusarium oxysporum isolates from tobacco fields in Spain

Several formae speciales of Fusarium oxysporum are capable to produce disease in tobacco plants. Different authors have classified those isolates as a forma specialis or a race within on the basis of the severity of disease and host specificity. Fusarium wilt of tobacco plant in Extremadura (central Spain) tobacco fields have been recorded in the last years and F. oxysporum was isolated from symptomatic plants. The aim of our study was to characterize these F. oxysporum populations. For this purpose, the in vitro spore production and growth and the virulence (severity of disease) have been tested. Although all isolates behaved as pathogen, the virulence of isolates was different. The differences in growth could not be correlated with other characteristics but the two isolates with scarce spore production have also behaved as the weakest pathogen. We have analyzed intergenic spacer (IGS) region polymorphism of ribosomal DNA and random amplified polymorphic DNA (RAPD) markers to assess the genetic diversity within F. oxysporum isolates. These molecular analyses showed two major groups with different physiological capabilities that could reflect two different lineages. One group was characterized by medium–high sporulation, high virulence and the same IGS-RFLP pattern. The other group was more heterogeneous featuring low–medium sporulation and variable virulence and growth. This first experimental approach to pathogen population could be a good starting point for further studies including non-pathogenic isolates and a larger number of pathogen that could clarify if there are two or more genetic lineages.     

Early detection of Neophysopella tropicalis in grapevine leaves and on spore traps by qPCR

Neophysopella tropicalis, one of the causal agents of Asian grapevine leaf rust (AGLR), can cause severe epidemics in Brazil that lead to yield losses in commercial vineyards. An early detection of the pathogen by air sampling of urediniospores on spore traps or in symptomless leaves would be valuable to multiple studies, such as epidemics modelling, risk forecasting, monitoring of pathogen introductions in rust-free areas, and predicting the beginning of epidemics. This study developed a quantitative PCR (qPCR) protocol to quantify N. tropicalis urediniospores attached to adhesive tapes and in grapevine leaves before symptom appearance. A specific primer pair was designed based on the internal transcribed spacer (ITS) sequence region of the AGLR pathogen. Standard amplification curves using genomic DNA from urediniospores of N. tropicalis and from urediniospores attached to adhesive tapes were established. Grapevine leaves inoculated with N. tropicalis were collected at 2, 5, and 7 days postinoculation (dpi). One primer pair (580F/720R) amplified a 140 bp product in all AGLR isolates but did not amplify products of other rust genera, such as Phakopsora, Puccinia, Hemileia, Tranzschelia, Cerotelium, and Coleosporium. As little as 0.1 pg DNA and 10 urediniospores of N. tropicalis attached to adhesive tapes could be detected. qPCR enabled the detection of the pathogen as early as 2 dpi, before symptom appearance. This method can be used to monitor N. tropicalis inoculum in grapevine-growing areas and to quantify symptomless infections of the AGLR pathogen.     

PCR-based specific detection of <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> race 4 strains

Two primer sets were designed based on the sequence of polymorphic bands that were derived from repetitive sequence-based polymerase chain reaction (rep-PCR) fingerprinting and specifically detected in Ralstonia solanacearum race 4 strains (ginger, mioga, and curcuma isolates). One primer set (AKIF-AKIR) amplified a single band (165bp) from genomic DNA obtained from all mioga and curcuma and some ginger isolates; another set (21F-21R) amplified one band (125bp) from the other ginger isolates. These primer sets did not amplify the bands from genomic DNA of other R. solanacearum strains or of other related bacteria. PCR detection limit for the pathogen was 2 × 10²cfu.The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession numbers AB118756 and AB118757     

The Elegans fusaria causing wilt disease of carnation. I. Taxonomy

The distinction of the wilt disease pathogen of carnationFusarium (oxysporum var.)redolens fromF. oxysporum (var.oxysporum) is considered. Previous reports that isolates of both taxa cause indistinguishable diseases in carnation are confirmed.F. (oxysporum var.)redolens andF. oxysporum were found to form one variable complex on morphological criteria. Apparently, host specialization rather than morphological variation reflects the evolutionary relationships in theFusarium sectionElegans. The distinction ofF. redolens fromF. oxysporum does therefore not seem justified, neither at specific nor at varietal level.Samenvatting Het onderscheid tussenFusarium (oxysporum var.)redolens enF. (oxysporum var.)oxysporum als verwekkers van verwelkingsziekte bij anjer wordt ter discussie gesteld. Fytopathologisch onderzoek bevestigde vermeldingen in de literatuur dat voor anjer pathogene isolaten van beide soorten ziekten veroorzaken die niet te onderscheiden zijn; dit is ook bekend voor andere gewassen. Op morfologische gronden blekenF. (oxysporum var.)redolens enF. oxysporum één variabel complex te vormen. Kennelijk geeft de pathogene specialisatie inFusarium sectieElegans de evolutionaire verwantschappen beter weer dan de morfologische variatie. Het onderscheiden vanF. redolens naastF. oxysporum is daarom noch als soort, noch als variëteit gerechtvaardigd.     

Genetic variation among <Emphasis Type="Italic">Fusarium</Emphasis> isolates from onion,and resistance to <Emphasis Type="Italic">Fusarium</Emphasis> basal rot in related <Emphasis Type="Italic">Allium</Emphasis> species

The aim of this research was to study levels of resistance to Fusarium basal rot in onion cultivars and related Allium species, by using genetically different Fusarium isolates. In order to select genetically different isolates for disease testing, a collection of 61 Fusarium isolates, 43 of them from onion (Allium cepa), was analysed using amplified fragment length polymorphism (AFLP) markers. Onion isolates were collected in The Netherlands (15 isolates) and Uruguay (9 isolates), and received from other countries and fungal collections (19 isolates). From these isolates, 29 were identified as F. oxysporum, 10 as F. proliferatum, whereas the remaining four isolates belonged to F. avenaceum and F. culmorum. The taxonomic status of the species was confirmed by morphological examination, by DNA sequencing of the elongation factor 1-α gene, and by the use of species-specific primers for Fusarium oxysporum, F. proliferatum, and F. culmorum. Within F. oxysporum, isolates clustered in two clades suggesting different origins of F. oxysporum forms pathogenic to onion. These clades were present in each sampled region. Onion and six related Allium species were screened for resistance to Fusarium basal rot using one F. oxysporum isolate from each clade, and one F. proliferatum isolate. High levels of resistance to each isolate were found in Allium fistulosum and A. schoenoprasum accessions, whereas A. pskemense, A. roylei and A. galanthum showed intermediate levels of resistance. Among five A. cepa cultivars, ‘Rossa Savonese’ was also intermediately resistant. Regarding the current feasibility for introgression, A. fistulosum, A. roylei and A. galanthum were identified as potential sources for the transfer of resistance to Fusarium into onion.     

大豆枯萎病菌尖孢镰孢遗传多样性及大豆品种抗性

 了解大豆枯萎病菌的群体遗传特征及明确大豆种质对大豆枯萎病的抗性,对抗病育种、抗性品种的合理布局以及制定更有效的病害防治策略具有重要的参考价值。本研究利用随机扩增多态性DNA(random amplified polymorphic DNA,RAPD),对采自我国不同地区的大豆枯萎病菌—尖孢镰孢菌(Fusarium oxysporum)进行遗传多样性分析,筛选到10个多态性随机引物,共扩增出75条RAPD条带,其中55条为多态性条带,占73.3%。利用UPGMA法对DNA扩增图谱进行聚类分析,以相似系数0.68为阈值,55个分离物可分为9个遗传聚类组,表明我国大豆枯萎病菌具有丰富的种内遗传多样性,所划分的群体与分离物来源地不相关。同时,对上述分离物进行致病性分析,发现我国的大豆枯萎病菌具有明显的致病力分化现象。进一步利用3个代表性分离物对来自我国不同大豆产区的180个大豆品种(资源)进行抗大豆枯萎病鉴定,发现皖豆28、中黄13、中黄51、中作X08076和5D034等5个品种对大豆枯萎病具有良好抗性,占供试材料的2.8%,表明不同大豆品种对枯萎病的抗性存在一定的差异。     

Development of sequence tagged site markers to identify races of Fusarium oxysporum f. sp. lactucae

By random amplified polymorphic DNA (RAPD) analysis of the representative isolates of each race of Fusarium oxysporum f. sp. lactucae, RAPD fragments of 0.6, 1.6, and 2.9kb were obtained. The 0.6-kb RAPD fragment was common to the representative isolates of all three races. Amplification of the 1.6- and 2.9-kb fragments were unique to the isolates of races 1 and 2, respectively. Sequence tagged site (STS) marker FLA0001, FLA0101, and FLA0201 were generated from the 0.6-, 1.6-, and 2.9-kb RAPD fragments, respectively. Polymerase chain reaction (PCR) analysis showed that FLA0001 was common to all 49 isolates of F. oxysporum f. sp. lactucae. FLA0101 was specifically generated from all 23 isolates of race 1 but not from races 2 or 3. FLA0201 was specifically amplified from all 12 isolates of race 2 but not from races 1 or 3. In two isolates of F. oxysporum f. sp. lactucum, PCR amplified FLA0001 and FLA0101 but not FLA0201. On the other hand, these STS markers were not detected from isolates of five other formae speciales. Because these STS markers were not generated from isolates of other plant pathogenic fungi, bacteria, or plant materials examined in this study, PCR analysis combined with the three STS markers should be a useful means for rapid identification of races of F. oxysporum f. sp. lactucae.     

Genetic diversity of the root‐knot nematode Meloidogyne ethiopica and development of a species‐specific SCAR marker for its diagnosis

Meloidogyne ethiopica is an important nematode pathogen causing serious economic damage to grapevine in Chile. In Brazil, M. ethiopica has been detected with low frequency in kiwifruit and other crops. The objectives of this study were to evaluate the intraspecific genetic variability of M. ethiopica isolates from Brazil and Chile using AFLP and RAPD markers and to develop a species‐specific SCAR‐PCR assay for its diagnosis. Fourteen isolates were obtained from different geographic regions or host plants. Three isolates of an undescribed Meloidogyne species and one isolate of M. ethiopica from Kenya were included in the analysis. The results showed a low level of diversity among the M. ethiopica isolates, regardless of their geographical distribution or host plant origin. The three isolates of Meloidogyne sp. showed a high homogeneity and clustered separately from M. ethiopica (100% bootstrap). RAPD screenings of M. ethiopica allowed the identification of a differential DNA fragment that was converted into a SCAR marker. Using genomic DNA from pooled nematodes as a template, PCR amplification with primers designed from this species‐specific SCAR produced a fragment of 350 bp in all 14 isolates of M. ethiopica tested, in contrast with other species tested. This primer pair also allowed successful amplification of DNA from single nematodes, either juveniles or females and when used in multiplex PCR reactions containing mixtures of other root‐knot nematode species, thus showing the sensitivity of the assay. Therefore, the method developed here has potential for application in routine diagnostic procedures.     

实时荧光定量PCR法检测十字花科细菌性黑斑病菌

为有效防控我国的检疫性有害生物十字花科细菌性黑斑病菌Pseudomonas syringae pv.maculicola在国内的传播与蔓延,通过设计1对特异性引物3539,利用132株靶标和非靶标菌为模板进行PCR扩增,建立了实时荧光定量PCR法,并进行了模拟种子带菌试验。结果显示,引物3539为只针对十字花科细菌性黑斑病菌扩增出的特异性产物;在模拟种子带菌检测中,常规PCR对菌悬液的检测限为10~5CFU/m L,实时荧光定量PCR的检测限为10~3CFU/m L,其中10~8CFU/m L菌液的Ct值最低,为22.90,10~3CFU/m L菌液的Ct值最高,为35.73,且不同浓度菌液间的Ct值均有显著差异;不同带菌率模拟种子的检测结果表明,常规PCR和实时荧光定量PCR能检测到的带菌率分别为0.5%和0.1%。研究表明,实时荧光定量PCR法不仅可用于病种的检测,也可用于病害的早期诊断。     

The elegans fusaria causing wilt disease of carnation. II. Distinction of vegetative compatibility groups

The vegetative compatibility patterns among isolates ofElegans fusaria causing wilt disease of carnation were investigated. Nitrate non-utilizing mutants were generated from 16 isolates labelledF. redolens, nine of which came from carnation, and from 33 isolates labelledF. oxysporum, 19 of which came from carnation. Pairings of the mutants revealed five vegetative compatibility groups among the isolates from carnation, corresponding withF. oxysporum f.sp.dianthi race 1 (VCG1), race 2 (VCG2) and race 4 (VCG3),F. redolens f.sp.dianthi (VCG4) andF. redolens isolates from foot rot-diseased carnations (VCG5). Besides three isolates typical ofF. redolens, VCG4 comprised a now slightly deviating subculture of the type isolate ofF. redolens f.sp.dianthi of which the cultural characteristics correspond toF. oxysporum instead ofF. redolens. This observation may be taken to support previous conclusions that the distinction between both taxa is not justified. Otherwise, the compatibility patterns did not provide decisive evidence to accept or reject conspecificity of both taxa. Isolates from carnation did not form heterokaryons with other formae speciales ofF. oxysporum.Samenvatting De vegetatieve compatibiliteitspatronen bij isolaten vanElegans-fusaria die verwelkingsziekte bij anjer veroorzaken werden onderzocht. Van 16 isolaten vanF. redolens, waarvan negen afkomstig van anjers, en van 33 isolaten vanF. oxysporum, waarvan 19 afkomstig van anjers, werden mutanten gegenereerd die zonder een organische stikstofbron geen luchtmycelium meer konden vormen. Paringen tussen mutanten van isolaten afkomstig van anjers brachten een vijftal vegetatieve compatibiliteitsgroepen aan het licht, die overeenkwamen metF. oxysporum f.sp.dianthi fysio 1 (VCG 1), fysio 2 (VCG 2) en fysio 4 (VCG3),F. redolens f.sp.dianthi (VCG4) enF. redolens isolaten afkomstig van aan voetrot lijdende anjers (VCG5). Naast drie voorF. redolens karakteristieke isolaten omvatte VCG4 ook een afwijkende subculture van het type-isolaat vanF. redolens f.sp.dianthi, die in cultuureigenschappen overeen kwam metF. oxysporum in plaats vanF. redolens. Deze waarneming geeft enige steun aan eerdere conclusies dat het onderscheid tussen beide taxa niet gerechtvaardigd is. Daarbuiten gaven de compatibiliteitspatronen geen uitsluitsel over de mogelijke conspecificiteit van beide taxa. Isolaten afkomstig van anjers vormden geen heterokaryons met andere formae speciales vanF. oxysporum.     

Vegetative Compatibility Grouping of Fusarium oxysporum f. sp. gladioli from Saffron

Fusarium corm rot of saffron (Crocus sativus L.), incited by Fusarium oxysporum f. sp. gladioli, causes severe yield losses in Italy. Major symptoms during flowering (October–November) include yellowing and wilting of shoots, basal stem rot and corm rot. Sixty-four isolates of F. oxysporum f. sp. gladioli, obtained from infected saffron crops located in Italy (Abruzzi, Tuscany and Umbria) and in Spain, were characterized by pathogenicity and vegetative compatibility. Chlorate-resistant, nitrate-nonutilizing (nit) mutants were used to determine vegetative compatibility among the isolates of the pathogen with the aim of examining the genetic relatedness among populations from different locations. All the isolates belonged to vegetative compatibility group 0340. Since saffron shares susceptibility to F. oxysporum f. sp. gladioli with other ornamental plants of the Iridaceae (Crocus, Gladiolus, Iris and Ixia), it is likely that a clone of the pathogen (VCG 0340) was introduced with other hosts and is responsible for the disease outbreak observed on saffron in Italy. Alternatively, or additionally, the clone of F. oxysporum f. sp. gladioli causing disease on saffron in other countries may have spread to the saffron fields in Italy through the import and dispersal of infested propagation material.