Genetic diversity in Fusarium oxysporum f.sp. dianthi and Fusarium redolens f.sp. dianthi

Pathogenic isolates were selected representing all known vegetative compatibility groups (VCGs) and races of Fusarium oxysporum sensu lato from Dianthus spp. On basis of differences in the internal transcribed spacer region of the ribosomal DNA, six VCGs were classified as F. oxysporum f.sp. dianthi and four as F. redolens f.sp. dianthi. All VCGs of F. oxysporum f.sp. dianthi were characterized by unique restriction fragment length polymorphisms (RFLPs), unique overall esterase profiles, and unique virulence spectra, supporting a clonal lineage concept. Two VCGs of F. oxysporum f.sp. dianthi nevertheless comprised more than one race, but races within the same VCG shared the same distinct overall virulence spectrum. VCGs belonging to F. redolens f.sp. dianthi also had unique RFLPs and unique virulence spectra, but had grossly identical esterase profiles. Three new races (9, 10 and 11) are described for F. oxysporum f.sp. dianthi, and four for F. redolens f.sp. dianthi. Two races previously considered lost were recovered; race 7 was identified as a member of VCG 0021 of F. oxysporum f.sp. dianthi while race 3 was identified as a distinct VCG and race of F. redolens f.sp. dianthi. A summary of races and VCGs in F. oxysporum f.sp. dianthi and F. redolens f.sp. dianthi is presented.     

Electrophoretic karyotype variation among pathotypes of Fusarium oxysporum f.sp. dianthi

Karyotype analysis by pulsed-field gel electrophoresis was applied to characterize isolates of Fusarium oxysporum f.sp. dianthi , the causal agent of Fusarium wilt on carnation. Eleven distinct chromosomal DNA patterns were detected among 38 pathogenic isolates, and the total genome size was estimated to range from 23·7 to 36·4 Mb. Except for isolates belonging to pathotypes 2 and 4 , all members of the same pathotype shared overlapping electrophoretic karyotypes. Karyotypes of isolates assigned to pathotypes 1 and 8 showed a high degree of similarity, in accordance with VCG and RFLP analysis. The same electrophoretic karyotype was also shared by members of pathotypes 2 and 5, thus confirming results obtained by both VCG and RFLP grouping, A single representative of pathotype 6, previously confined to the same VCG and RFLP group as pathotypes 2 and 5, had a slightly different chromosomal pattern. Isolates assigned to pathotype 4 showed four related karyotypes which partially differed in both the number and size of chromosomal bands. However, all strains assigned to this pathotype shared a basic profile of nine chromosomal bands, while two low-molecular-weight bands were present or absent. The findings are discussed with regard both to the suitability of race distinction in the case of the special form dianthi of F. oxysporum and to the use of karyotype analysis by PFGE as a tool for the study of the population genetics of this fungus.     

Vegetative compatibility of Fusarium oxysporum f.sp. dianthi from carnation in Israel

Auxotrophic mutants were used to determine vegetative relatedness among isolates of Fusarium oxysporum f.sp. dianthi (F.o.d.) , the vascular wilt pathogen of carnation. At the first stage, different nitrate-non-utilizing (nit) mutants were produced from 11 isolates of F.o.d. collected in Israel. Complementation (heterokaryon) tests showed that all the isolates belonged to a single vegetative compatibility group (VCG), and two mutants were chosen as its testers. Additional isolates of Fusarium from carnation, collected during 1986-88, were analysed for pathogenicity and vegetative compatibility with the testers. A total of 170 Fusarium isolates, obtained from 42 cultivars at 40 sites, were tested. All the nit mutants of all the 132 pathogenic isolates formed heterokaryons with the testers, indicating that they belonged to the same VCG. None of the 38 non-pathogenic isolates was vegetatively compatible with the testers. The nit mutants retained pathogenicity to carnation. The F.o.d. testers were not compatible with testers of five other formae speciales of F. oxysporum. Thus, F.o.d. appears to constitute a distinct genetic population within the F. oxysporum complex.     

Response of carnation cultivars to Fusarium oxysporum f.sp. dianthi in the field

The response of carnation (Dianthus caryophyllus L.) cultivars toFusarium oxysporum f.sp.dianthi (F.o.d.) was evaluated in an artificially infested field from 1988/9 to 1991/2. Disease incidence was highly correlated with disease severity, indicating that disease incidence may be used to estimate the impact ofF.o.d. on the host. Based on the results, the following stepwise procedure was developed for characterizing the response of carnation cultivars toF.o.d. First, the general response of the tested cultivar was classified as resistant or susceptible on the basis of disease incidence values recorded 180 days after planting. Empirical analysis of the data revealed that a disease incidence level of 75% may be taken as a reliable cut-off point for separation of cultivars into the two groups. Within each group, cultivars were then subjected to a more explicit classification: in the resistant group the records of actual disease incidence were used for classification, while in the susceptible group the linear rearrangement of the disease progress curve was calculated according to the Gompertz function, and the value of the intercept was used for classification.Contribution No. 3539-E series, from the Agricultural Research Organization.     

Induced resistance in tomato plants against Fusarium wilt invoked by Fusarium oxysporum f.sp. dianthi

Tomato plants, susceptible toFusarium oxysporum f. sp.lycopersici, were inoculated by immersing the roots in a conidial suspension ofF. oxysporum f. sp.lycopersici race 1,F. oxysporum f. sp.dianthi race 2 or a mixture of both fungi. Plants inoculated withF. oxysporum f. sp.lycopersici showed disease symptoms after 2 weeks, whereas plants inoculated withF. oxysporum f. sp.dianthi or a mixture of both fungi remained symptomless for over 7 weeks, the duration of the experiment. In another experiment root systems of plants were split and each half was separately inoculated. One half was firstly inoculated withF. oxysporum f. sp.dianthi or treated with water, followed after a week by a second inoculation of the other half withF. oxysporum f. sp.lycopersici or by a water treatment. The disease symptoms in the half firstly inoculated withF. oxysporum f. sp.dianthi were significantly delayed, compared to plants of which that half had been treated with water. BecauseF. oxysporum f. sp.dianthi reduced disease symptoms caused byF. oxysporum f. sp.lycopersici without any direct interaction with this pathogen, it is concluded thatF. oxysporum f. sp.dianthi is able to induce resistance againstF. oxysporum f. sp.lycopersici in tomato plants.     

Effect of mixed inoculations with Fusarium oxysporum f. sp. lycopersici and F. oxysporum f. sp. dianthi on the phenols content of tomato plants

Forms ofFusarium oxysporum specific on hosts other than tomato induce in this plant greater initial increases of the phenols content than the pathogenic f. sp.lycopersici. Mixed inoculations of f. sp.lycopersici and f. sp.dianthi are on the contrary no more effective in inducing the phenol accumulation 24 h after the infection than f. sp.lycopersici alone. This observation suggests that the pathogen can suppress the phenolic response that is typical of the incompatible combinations.Samenvatting Vormen vanFusarium oxysporum welke pathogeen zijn voor andere planten dan de tomaat induceren in deze plant aanvankelijk een grotere toename van het fenolgehalte dan de pathogene f. sp.lycopersici. Inoculaties met een gemengd inoculum van de f. sp.lycopersici en f. sp.dianthi hebben daarentegen geen groter effect op de toename van het fenolgehalte 24 uur na infectie dan de inoculaties met f. sp.lycopersici alleen. Verondersteld wordt dat het pathogeen de toename van het fenolgehalte, dat typerend is voor de incompatibele combinatie, kan onderdrukken.     

Passive transport of microconidia of Fusarium oxysporum f. sp. dianthi in carnation after root inoculation

Root inoculation of susceptible carnations withFusarium oxysporum f. sp.dianthi induced characteristic unilateral wilt only if root woundings and use of a microconidial suspension had not been combined at the time of inoculation. The combination, however, induced atypical and sudden stem breaking soon followed by death. In all cases wilt was due to destruction of the xylem. Unilateral wilt appeared to follow sparse natural infection of single roots. Stem breaking was due to destruction of the vascular tissues all around the stem and is ascribed to multilateral infection caused by translocation of microconidia at inoculation through several wounded roots directly into the stem.Microconidia were carried passively 5–10(–10) cm into stems of susceptible and resistant carnations within 24 h both after immersing cut ends of the roots in a conidial suspension and after pouring a suspension on the soil. Passive spore transport is an inoculation artefact which may severely affect interpretation of experimental results; it seems to be unimportant in natural Fusarium wilt development in carnation.Samenvatting Inoculatie van de wortels van vatbare anjers metFusarium oxysporum f. sp.dianthi veroorzaakte de kenmerkende eenzijdige verwelking alleen als wortelbeschadigingen bij de inoculatie niet werden gecombineerd met het gebruik van een suspensie van microconidiën. Die combinatie veroorzaakte namelijk afwijkende symptomen waarbij de planten plotseling omknakten en vervolgens snel afstierven. De verwelking leek in alle gevallen veroorzaakt te worden door afbraak van het xyleem. Eenzijdige verwelking leek te volgen op spaarzame natuurlijke wortelinfecties. Bij omgeknakte planten bleek het vaatweefsel rondom in de stengel aangetast te zijn, hetgeen toegeschreven wordt aan infectie van verschillende kanten van de stengel als gevolg van passief transport van microconidiën bij de inoculatie door verscheidene beschadigde wortels direct de stengel in.Microconidiën werden binnen 24 uur 5–10(–30) cm de stengels van vatbare en resistente anjers ingezogen wanneer de wortels afgesneden en met het uiteinde in een sporensuspensie gehangen werden, maar ook wanneer de suspensie op de grond gegoten werd. Passief transport van sporen is een inoculatie-artefact dat echter belangrijke consequenties kan hebben voor de interpretatie van de resultaten van proeven. Bij de natuurlijke verspreiding vanF. oxysporum in anjers lijkt passief sporentransport van weinig belang.     

Involvement of phenol metabolism in resistance of Dianthus caryophyllus to Fusarium oxysporum f.sp. dianthi

Three carnation cultivars were investigated for the effect of stem inoculation withFusarium oxysporum f.sp.dianthi on production of phenolic compounds and on fungistatic activity. Carnation stems were characterized by a complex mixture of cell wall-bound phenolics, several of which occurred in considerable amounts. Only very low amounts of phenolic compound were present in the vacuoles.Infection withF. oxysporum f.sp.dianthi induced the production and accumulation of a number of new compounds, both free in the cell sap and bound to the cell wall. In addition, the stem extracts acquired germination-inhibiting properties for conidia of the fungus. The accumulation of several phenolics and the fungistatic activity were roughly correlated to the degree of resistance of the three cultivars. Part of the differences in their resistance toF. oxysporum f.sp.dianthi might be due to an inhibition of the conversion of phenolic acid-type precursors into phytoalexins in the more susceptible cultivars.Samenvatting Drie anjercultivars werden onderzocht op de effecten van stengelinoculatie metFusarium oxysporum f.sp.dianthi op de produktie van fenolische verbindingen en op de fungistatische activiteit van stengelextracten. Anjerstengels bleken een complex mengsel van celwand-gebonden fenolzuren te bevatten, waarvan er verschillende in vrij grote hoeveelheden voorkwamen. Daartegenover waren de hoeveelheden fenolische verbindingen in de vacuole bij gezonde anjerstengels erg laag.Infectie metF. oxysporum f.sp.dianthi induceerde de produktie en accumulatie van een aantal nieuwe verbindingen in het celsap, alsook gebonden aan de celwand. Tevens bleek de remming van de kieming van conidiën vanF. oxysporum f.sp.dianthi onder invloed van deze stengelextracten sterk verhoogd, in vergelijking met de remming veroorzaakt door extracten van gezonde stengels. De accumulatie van een aantal fenolen en de verhoging van de fungistatische activiteit van de extracten waren in grote lijnen gecorreleerd met de uit de praktijk bekende resistentie van de drie cultivars. De verschillen in resistentie tegenF. oxysporum f.sp.dianthi zouden deels kunnen berusten op remming van de omzetting van precursors (fenolzuren) in fytoalexinen in de meer vatbare cultivars.     

Reductive detoxification of the acetophenone skeleton of the carnation phytoanticipin by Fusarium oxysporum f.sp. dianthi

The skeleton of the carnation phytoanticipin, acetophenone, was detoxified by Fusarium oxysporum f.sp. dianthi , the main fungal parasite of carnation. This process consisted of the reduction to ethanol of the acetyl group, leading to the formation of phenylethanol, which has lower fungitoxic activity than the parent molecule. The conversion took place through the activity of an adaptive fungal oxidoreductase, which was NADH-dependent and was released by the fungus as two enzymatic forms within the culture substrate in the presence of acetophenone. Reduction was stereospecific and gave rise to only one of the two possible enantiomeric forms.     

Selection methods for determining resistance of carnation cultivars to Fusarium oxysporum f.sp. dianthi

The level of resistance of carnation ( Dianthus caryophyllus ) cultivars to wilt caused by Fusarium oxysporum f.sp. dianthi was compared in root-dip-inoculated plants grown in pots (filled with tuff or sandy soil) in a greenhouse and plants grown in a field where the soil was artificially infested with the fungus. In the field, wilt symptoms appeared first in susceptible and subsequently in resistant cultivars; none was immune. Variations in the level of resistance were expressed either by different percentages of wilted plants (i.e. disease incidence) or by delayed disease progress as compared to a susceptible cultivar. The range of disease severity in the field, ranked on a scale from 0 to 4, was highly and significantly correlated with the percentage of diseased plants. The greenhouse test was unreliable as a predictor of the degree of resistance observed in the field. Similar wilt levels in the greenhouse and the field were found only in susceptible cultivars.     

Colonization and histopathology of susceptible and resistant carnation cultivars infected with Fusarium oxysporum f. sp. dianthi

Stems of the susceptible Early Sam and resistant Novada carnations were inoculated with a conidial suspension ofFusarium oxysporum f. sp.dianthi. Stem segments of either cultivar were sampled regularly and used for determination of fungal growth and for microscopical investigation.Early Sam showed typicalFusarium wilt symptoms and its stems were colonized intensively. The observed vascular browning appeared to be caused by discolouration of primary walls of infected vessels and surrounding cells. Vessels were rarely occluded with gel. Cell wall degradation led to the formation of stem cavities. Hyperplasia of xylem parenchyma was not seen.In Novada, fungal colonization remained low throughout the experiment. Macroscopic symptoms were absent except for longitudinal bursts in the stem, which appeared to be caused by hyperplasia of xylem parenchyma bordering infection. Vascular gelation occurred in the infected tissues, causing some vascular browning also. Xylem vessel regeneration was observed in the hyperplastic layer. Cavities were not formed, and wall discolouration was rare. Vascular gelation is considered part of theFusarium wilt resistance mechanism. It is followed by xylem vessel regeneration, which expresses a general plant response to vascular dysfunction rather than being part of the resistance mechanism.Although of different origin, vascular browning as such occurs in both susceptible and resistant interactions. In breeding for resistance, care should hence be taken with the current use of browning as an indication of disease.Samenvatting Anjers van de vatbare cultivar Early Sam en de resistente cultivar Novada werden geïnoculeerd met een conidiënsuspensie vanFusarium oxysporum f. sp.dianthi. Van beide cultivars werden regelmatig stengeldelen geoogst om deze microscopisch te onderzoeken en om de schimmelgroei te bepalen.Early Sam vertoonde de voor deze verwelkingsziekte kenmerkende symptomen en werd intensief gekoloniseerd. Aan het vaatweefsel waargenomen bruinkleuring bleek veroorzaakt te worden door verkleuring van de primaire wanden van geïnfecteerde vaten en de hen omringende cellen. Zelden trad er in de vaten gomvorming op. Celwandafbraak veroorzaakte de vorming van holten in de stengel. Hyperplasie van het houtparenchym werd niet waargenomen.In Novada bleef de schimmelgroei gedurende het hele experiment beperkt. Macroscopisch waren er enkel lengtescheuren in de stengel te zien, die veroorzaakt bleken te worden door hyperplasie van aan de infectie grenzend houtparenchym. In het geïnfecteerde vaatweefsel optredende gomvorming veroorzaakte ook enige bruinkleuring. In het hyperplastische weefsel werd regeneratie van houtvaten waargenomen. In de stengel werden geen holten gevormd, en verkleuring van de celwanden kwam weinig voor. De vorming van gommen in de houtvaten maakt waarschijnlijk deel uit van het resistentiemechanisme. De daarop volgende houtvatregeneratie is eerder een algemene reactie van de plant op vaatverstopping dan een deel van het resistentiemechanisme.Vaatverbruining, zij het van verschillende oorsprong, komt voor in zowel vatbare als resistente interacties. Om die reden moet men in de resistentieveredeling bij de anjer voorzichtig zijn met het gebruik van bruinkleuring als ziekteïndicatie.     

Examination of the relationships between vegetative compatibility groups and races in Fusarium oxysporum f.sp. dianthi

The feasibility of identifying races of Fusarium oxysporum f.sp. dianthi by tests for vegetative compatibility type was investigated. Nitrate non-utilizing nitl and NitM mutants were generated from 51 isolates of F. oxysporum f.sp. dianthi , 18 isolates of f. oxysporum from Dianthus spp. not belonging to f.sp. dianthi and, for comparison, 11 isolates of F. proliferatum from Dianthus spp. Vegetative compatibility groups (VCGs) among the isolates were identified by pairing all nitl with all NitM mutants.
Vegetative compatibility was found between isolates of F. oxysporum f.sp. dianthi races 1 and 8 (VCG 0022), races 2, 5 and 6 (VCG 0021) and race 4 (VCG 0020), and wilt-causing isolates previously classified as F. redolens from D. caryophyllus (VCG 0023) and D. barbatus (VCG 0024), Three self-compatible wilt-causing isolates were vegetatively incompatible with all other isolates (VCGs 0025,0026 and 0027), Two VCGs were found among isolates of F. oxysporum from D. caryophyllus not belonging to f.sp. dianthi ; six non-pathogenic isolates were self-compatible but vegetatively incompatible with all other isolates. The foot-rot-associated isolates of F. proliferatum from D. caryophyllus constituted a separate VCG.
Virulence analyses revealed at least four new races among VCGs 0023 to 0027, New Isolates could be categorized as races as a result of VCG analysis and VCG classification correctly indicated that the race identities previously ascribed to two old isolates had been incorrect. Vegetative compatibility tests offer the prospect for rapid identification of races, although inoculation tests continue to be necessary to differentiate races that belong to a single VCG.     

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.     

Effects of abiotic variables on the response of carnation cultivars to Fusarium oxysporum f.sp. dianthi

The effects of abiotic variables on the response of carnation cultivars to Fusarium oxysporum f.sp. dianthi ( F.o. dianthi  ) were examined in experiments conducted under semi-controlled environments. The abiotic variables examined were solar radiation intensity, temperature and growth substrate. Temperature was not controlled, but differed markedly among experiments, thus, its effect was not determined quantitatively. Disease incidence and disease severity varied significantly among the experiments (due mainly to differences in temperature), among the solar radiation treatments and among the cultivars tested. The three-way interaction term (i.e. cultivar × shade treatment × experiment) was highly significant ( P  < 0.001) when both disease incidence and disease severity were considered, indicating that no single variable was predominant in determining disease intensity. The effects of the growth substrate on disease progress was examined in plants grown in tuff or in tuff mixed with peat (1 : 1 and 1 : 3) substrates. The growth substrate had a potent effect on disease development in the less susceptible cultivars. Severe epidemics developed in all cultivars when they were grown in the tuff/peat mixture, although some were resistant when grown in tuff alone. These results led to the conclusion that the carnation response to F.o. dianthi is substantially influenced by the environmental conditions of the test.     

Differences in pathogenesis observed among susceptible interactions of carnation with four races of Fusarium oxysporum f.sp. dianthi

Susceptible interactions of Early Sam carnations with races 1,2,4, and 8 ofFusarium oxysporum f. sp.dianthi differed in pathogenesis, both after stem and after root inoculation. Race 1 induced pallescence and withering of leaves. Affected vascular tissue had a uniform pallid to pale brown colour; though heavily colonized, it was not or virtually not degraded. Defence reactions developed only slowly. Race 2 induced yellowing, of the midribs in particular, and withering of leaves. Affected vascular tissue was white with dark brown margins. Colonized tissue was degraded to leave vascular cavities. At lower heights of colonization, many defence reactions developed, which sometimes resulted in localization of the pathogen. Race 4 induced a similar pathogenesis as race 2, except for less intensive defence reactions. Race 8 induced midrib lesions on, and pallescence, withering and necrosis of leaves. Affected vascular tissue had a uniform light brown colour. Degradation of colonized vascular tissues was rare; instead, many defence reactions were observed, even at high heights in the plants.Races 1, 2 and 4 ofF. oxysporum f. sp.dianthi did not induce disease symptoms in Novada carnations, known to be highly resistant to race 2. Stem-inoculated plants localized the infection close to the inoculation site; stems of root-inoculated plants remained unaffected. The localization response also occurred in Early Sam and Novada carnations stem-inoculated withF. oxysporum f. sp.lycopersici.Samenvatting Tussen interacties van Early Sam-anjers met fysio's 1, 2, 4 en 8 vanF. oxysporum f. sp.dianthi werden verschillen in ziekteontwikkeling gevonden na wortel-zowel als stengelinoculatie. Fysio 1 gaf verbleking en verdroging van de bladeren. Aangetast vaatweefsel was gelijkmatig vaal of lichtbruin van kleur, en werd hevig gekoloniseerd, maar vrijwel niet afgebroken. Afweerreacties kwamen slechts traag op gang. Fysio 2 gaf vergeling, in het bijzonder van de hoofdnerven, en verdroging van de bladeren. Aangetast vaatweefsel was wit met donkerbruine randen. Gekoloniseerd weefsel werd afgebroken, hetgeen leidde tot de vorming van holten in het vaatweefsel. In de lagere gekoloniseerde delen traden veel afweerreacties op, hetgeen soms lokalisatie van het pathogeen tot gevolg had. Fysio 4 gaf eenzelfde ziekteontwikkeling als fysio 2, maar minder afweerreacties. Fysio 8 gaf lesies bij de hoofdnerven, en verbleking, verdroging en necrose van bladeren. Aangetast vaatweefsel was gelijkmatig lichtbruin van kleur. Afbraak van gekoloniseerd vaatweefsel werd zelden waargenomen; veel afweerreacties vergezelden de kolonisatie tot hoog in de stengel.Inoculatie van Novada anjers met fysio's 1,2 en 4 vanF. oxysporum f. sp.dianthi had geen ziektesymptomen tot gevolg. Via de stengel geïnoculeerde planten lokaliseerden de infectie ter hoogte van het inoculatiepunt; de stengels van via de wortels geïnoculeerde planten waren onaangetast. De lokalisatiereactie trad ook op in Early Sam en Novada anjers na inoculatie via de stengel metf. oxysporum f. sp.lycopersici.     

Restriction fragment length polymorphisms in Fusarium oxysporum f.sp. dianthi and other fusaria from Dianthus species

DNA restriction fragment length polymorphisms (RFLPs) among 46 isolates of Fusarium oxysporum from Dianthus spp., representing the known range of pathogenicity in carnation, were determined using total DNA digested with the restriction enzyme Hind III and a previously described probe, D4. Distinct multiple band RFLP patterns were found, which delineated RFLP groups as follows: (i) F. oxysporum f.sp. dianthi races I and 8; (ii) F. oxysporum f.sp. dianthi races 2, 5 and 6; (iii) F. oxysporum f.sp. dianthi race 4; (iv) a recently described race of F. oxysporum f.sp. dianthi (wilt-causing isolates from D. caryophyllus formerly classified as F. redolens); (v) wilt-causing isolates from D. barbatus formerly classified as F. redolens and (vi), (vii) and (viii), three further recently described races of F. oxysporum f.sp. dianthi. Isolate groups derived from analysis of RFLPs were consistent with existing and recently described vegetative compatibility groups (VCGs) in F. oxysporum f.sp. dianthi , but not in all cases with races. Isolates of F. oxysporum and F. proliferatum not associated with wilt disease had simpler RFLP patterns (with one exception) that were not associated with VCGs.     

New evidence of intra-race diversity in Fusarium oxysporum f. sp. dianthi populations based on Vegetative Compatibility Groups

Fusarium oxysporum f. sp. dianthi (Fod) causes vascular wilt, the most important carnation disease worldwide. We have analyzed vegetative compatibility in a collection of Fod isolates, obtained from both soils and carnation plants in the most important growing areas in Spain, by pairing all isolates in all possible combinations. Results showed that isolates of race 1 and race 2 were distributed among three Vegetative Compatibility Groups (VCG) which correlated with the molecular Groups previously described. Isolates of race 1 and race 2 in molecular Group I grouped in VCG 0021, isolates of race 1 type were in VCG 0022, and isolates of race 1 and race 2 in molecular Group II constituted a new VCG (002-), not previously reported. Isolates in each VCG contained the same mating type gene (MAT1-1 or MAT1-2), with the exception of the new VCG 002- that contained both idiomorphs. This work identifies a new VCG in Fod populations and reports for the first time the presence of isolates of race 1 and race 2 in the same VCG.     

Gene genealogies support Fusarium oxysporum f. sp. ciceris as a monophyletic group

Fusarium oxysporum f. sp. ciceris (Foc), the causal agent of fusarium wilt of chickpea, consists of two pathotypes (yellowing and wilting) and eight races (races 0, 1B/C, 1A and 2–6) of diverse geographical distribution. Six Foc isolates, one each of races 0, 1B/C, 1A, 4, 5 and 6, representing the two pathotypes and the geographical range of the pathogen, showed identical sequences in introns of the genes for translation elongation factor 1α ( EF1 α), β-tubulin, histone 3, actin and calmodulin. Eleven additional Foc isolates representative of all races, pathotypes and geographical range, and three isolates of F. oxysporum (Fo) nonpathogenic to chickpea were further analysed for sequence variation in the EF1 α gene. All isolates pathogenic to chickpeas shared an identical EF1 α gene sequence, which differed from that shared by the three Fo isolates nonpathogenic to chickpea. EF1 α gene sequences from the 17 Foc isolates and the three Fo isolates were compared with 24 EF1 α gene sequences in GenBank from isolates of 11 formae speciales of F. oxysporum by parsimony analysis. Foc isolates formed a grouping distinct from other formae speciales and nonpathogenic isolates. These results indicate that F. oxysporum f. sp. ciceris is monophyletic.     

Histology of roots of resistant and susceptible carnation cultivars from soil infested with fusarium oxysporum f.sp. dianthi

Fusarium wilt-resistant Novada and wilt-susceptible Early Sam carnations were planted in soil infested withFusarium oxysporum f.sp.dianthi, and their roots studied after five and ten weeks. Both in Novada and Early Sam, the extravascular tissue of undamaged young root parts were scarsely colonized. In roots of Novada, infected xylem vessels were usually occluded with gums and surrounded by phellem tissue. In mature parts of roots, the phellem surrounding occluded vessels often merged with the external phellem surrounding the vascular cylinder, after which the occluded vessels were shed from the roots. The phellem at the root surface appeared to be a strong barrier to fungal invasion. In roots of Early Sam carnations, as well as in a few roots of Novada carnations, the defence responses did not result in compartmentation of the fungus, and colonization and degradation of the vascular tissues followed. Diseased roots finally healthy. Shoots of Early Sam carnations, and eventually a few shoots of Novada carnations, were colonized and developed wilt symptoms.Samenvatting Resistente Novada en vatbare Early Sam anjers werden geplant in grond besmet metFusarium oxysporum f.sp.dianthi. Na vijf en tien weken werden de wortels van de planten bestudeerd. De extravasculaire delen van onbeschadigde jonge wortelgedeelten waren in beide cultivars nauwelijks gekoloniseerd. In de wortels van Novada waren geïnfecteerde houtvaten meestal verstopt door gommen en omgeven door kurkweefsel. In oudere wortelgedeelten sloot het kurkweefsel rond verstopte vaten vaak aan op het kurkweefsel aan de buitenkant van het vaatweefsel, waarna de aangetaste vaten werden uitgestoten uit de wortel. Het kurkweefsel aan het worteloppervlak leek een belangrijke barrière te vormen tegen het binnendringen van de schimmel. In de wortels van Early Sam en in enkele wortels van Novada mislukte het afweerproces, en werd het vaatweefsel door de schimmel gekoloniseerd en vervolgens afgebroken. Aangetaste wortels werden na afloop van tijd hol. De bovengrondse delen van de meeste Novada anjers werden niet gekoloniseerd en bleven gezond. De bovengrondse delen van de Early Sam anjers, en op den duur die van enkele Novada anjers, werden gekoloniseerd en verwelkten.