Physiological races and vegetative compatibility groups within Fusarium oxysporum f.sp. gladioli

The pathogenicity and vegetative compatibility of mainly Dutch isolates ofFusarium oxysporum collected from diseased gladioli and other Iridaceae were investigated. Based on their pathogenicity to two differential gladiolus cultivars, the isolates could tentatively be divided into two races. All self-compatible isolates ofFusarium oxysporum f.sp.gladioli belonged to one of three distinct vegetative compatibility groups, VCG 0340, 0341 or 0342, and were incompatible with isolates that were not pathogenic to gladiolus. Isolates of one of the two races were restricted to one VCG while isolates of the other race were present in all three VCGs.     

Physiological races and vegetative compatibility groups of butterhead lettuce isolates of Fusarium oxysporum f. sp. lactucae in Japan

Races were identified among butterhead lettuce isolates of Fusarium oxysporum f. sp. lactucae collected from three geographical areas of Hokkaido, Shizuoka, and Fukuoka in Japan by inoculation tests using Fujinagas race differential cultivars of lettuce (i.e., Patriot, Costa Rica No. 4, and Banchu Red Fire). Eighteen isolates from Shizuoka and Fukuoka were designated race 3, with two unknown vegetative compatibility groups (VCGs) that differed from Ogisos VCG 1 and 2. These two new VCGs were obtained from both Shizuoka and Fukuoka. On the other hand, three isolates from Hokkaido were classified as race 1 and identified as VCG 1, which represents a VCG of crisphead isolates from Nagano.     

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.     

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.     

Molecular identification of two vegetative compatibility groups of Fusarium oxysporum f. sp. cepae

Fusarium oxysporum f. sp. cepae, which causes basal rot of onion, consists of seven vegetative compatibility groups (VCGs 0420 to 0426) and several single-member VCGs (SMVs). F. oxysporum f. sp. cepae populations in South Africa and Colorado each consist of one main VCG (namely, VCG 0425 and 0421, respectively). The aim of this study was to develop sequence-characterized amplified region (SCAR) markers for the identification of VCGs 0425 and 0421, using 79 previously characterized F. oxysporum isolates. A second aim was to investigate the prevalence of VCG 0425 among 88 uncharacterized South African onion F. oxysporum isolates using (i) the developed SCAR markers and (ii) inter-retrotransposon (IR)- and random amplified polymorphic DNA (RAPD) fingerprinting. Only two RAPD primers provided informative fingerprints for VCG 0425 isolates but these could not be developed into SCAR markers, although they provided diagnostic fragments for differentiation of VCG 0425 from VCG 0421. IR fingerprinting data were used to develop a multiplex IR-SCAR polymerase chain reaction method for the identification of VCG 0421, VCG 0425, and SMV 4 isolates as a group. Molecular identification of the uncharacterized collection of 88 F. oxysporum isolates (65 F. oxysporum f. sp. cepae and 23 F. oxysporum isolates nonpathogenic to onion) confirmed that VCG 0425 is the main VCG in South Africa, with all but 3 of the 65 F. oxysporum f. sp. cepae isolates having the molecular characteristics of this VCG. Genotyping and VCG testing showed that two of the three aforementioned isolates were new SMVs (SMV 6 and SMV 7), whereas the third (previously known as SMV 3) now belongs to VGC 0247.     

Restriction fragment length polymorphisms, races and vegetative compatibility groups within a worldwide collection of Fusarium oxysporum f.sp. gladioli

Isolates of Fusarium oxysporum f.sp. gladioli were collected from widely different geographic areas. These isolates were characterized by pathogenicity to two differential gladiolus cultivars, vegetative compatibility, and total genomic DNA restriction fragment length polymorphisms (RFLPs). RFLPs were used to estimate the genetic divergence and relationship among isolates of F. oxysporum. RFLPs were detected by Southern blot hybridization of total genomic DNA with a 3-4 kb DNA probe generated from total DNA off. oxysporum f.sp. dianthi. Cluster analysis allowed the division of pathogenic strains into three main RFLP groups, each group containing strains with similarity coefficients ranging from 78 to 100%. RFLP groups correlated with vegetative compatibility groups, not with races. Two single pathogenic isolates which could not be assigned to any of the three main vegetative compatibility groups also had distinctive RFLP patterns. Little genetic polymorphism was observed within vegetative compatibility groups, whereas the majority of RFLPs occurred between vegetative compatibility groups, suggesting a common ancestry for strains within a specific vegetative compatibility group and a polyphyletic origin for the present special form gladioli.     

Population structure of Fusarium oxysporum f. sp. radicis-lycopersici in Florida inferred from vegetative compatibility groups and microsatellites

Fusarium crown and root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL) is a serious soilborne disease reducing tomato yields in Florida, a leading state in fresh market tomato production in the United States. One hundred and twenty five isolates of FORL were collected from the three main tomato-growing counties in Florida between 2006 and 2008. Vegetative compatibility groups (VCGs) and 10 microsatellite loci were used to infer the population structure of FORL. Up to 69.8 % of the isolates could be assigned to one of three VCGs, 0094, 0098 or 0099, with frequencies of 38.6, 24.4, and 6.8 % respectively. A medium level of population differentiation (Φst?=?0.159) was detected among the three counties, and three optimal clusters (populations) were supported by discriminant analysis of principal components. In addition, each population had some individuals that likely migrated from other populations. Migration probably played an important role in shaping the population structure of FORL since repeated VCGs and multilocus genotypes were observed in the three counties. Considerable migrants (> 1.33 migrants per generation) were also detected between the three counties, resulting in an increase in the effective population size and genetic diversity of F. oxysporum f. sp. radicis-lycopersici. Although migration is an important evolutionary force, mutation and parasexual recombination could not be completely ruled out as contributing causes to the genetic diversity of FORL. Management strategies that limit the movement of F. oxysporum f. sp. radicis-lycopersici are necessary to reduce the evolutionary potential of the pathogen.     

香荚兰尖孢镰刀菌营养体亲和性测定的初步研究

 Eight hundred twenty four nit mutants were induced from 73 strains of Fusarium oxysporum f. sp. vanillae, and classified into four phenotypes by their abilities to utilize different nitrogen sources. Among these mutants, 64.9% were characterized as nit 1, 24.3% as nit 3, 9.8% as nit M, 1.0% as nit X. Based on complementary pairing tests of different nit mutants on the medium MM, 44 isolates belonged to 8 different VCGs, 29 isolates were classified into single and different VCGs. These results indicated that there was significant VCG diversity in Fusarium oxysporum f. sp. vanillae population. VCGs might be correlated with geographic origin of strains, but no close correlation was found between VCGs and pathogenicity.     

黄瓜枯萎病菌毒力、营养体亲和性及ISSR分析

 本研究对来自哈尔滨、长春、沈阳、北京、西宁5个城市的70个尖孢镰刀菌黄瓜专化型菌株进行了毒力、营养体亲和性及ISSR分析。毒力测定结果显示黄瓜枯萎病菌在东农803品种上存在明显的毒力分化。在营养体亲和群的测定中有8个菌株没有产生nit突变体,2个菌株经测定为异核体自身不亲和性菌株,不能进行营养体亲和群的测定;其余60个菌株可分为5个营养体亲和群。利用筛选的7个引物对70个菌株进行了ISSR分子标记,聚类分析可将70个菌株分为3个类群,其中IGⅠ的41个菌株均来自东北三省,IGⅡ的21个菌株均来自北京,IGⅢ的8个菌株全部来自西宁。VCGs和ISSRs与菌株的地理来源及毒力存在一定的相关性。     

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.     

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.     

Physiological races of Fusarium oxysporum f.sp. melonis in Tunisia

Fusarium wilt of melon, caused by Fusarium oxysporum f.sp. melonis (Fom), is an important disease; races of the pathogen were identified by inoculating differential standard host cultivars. A total of ten isolates that were obtained from 23 fields located in four different geographical regions were identified as pathogenic. Results indicate that all four known Fom races, namely, 0, 1, 2 and 1.2, were found in north and middle Tunisia. Race 1.2 was the most prevalent.     

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.     

An assessment of aesculin hydrolysis, vegetative compatibility and DNA polymorphism as criteria for characterizing pathogenic races within Fusarium oxysporum f.sp. vasinfectum

Fifteen strains, assigned to four pathogenic races of Fusarium oxysporum f.sp. vasinfectum on the basis of host range, were characterized by means of vegetative compatibility, restriction fragment length polymorphisms (RFLPs) and pigmentation on aesculin-containing medium. Isolates were divided into two major vegetative compatibility groups (VCGs) comprising Races 1 and 2 (VI) and Race 3 (V2). The two VCGs were represented by a single RFLP pattern. An additional RFLP pattern was observed for a single Race 4 isolate. Isolates received as belonging to Races 2, 3 and 4 blackened aesculin agar, while designated and presumed Race 1 isolates gave a negative reaction.     

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.     

Inheritance of resistance in carnation against Fusarium oxysporum f.sp. dianthi races 1 and 2, in relation to resistance components

Four carnation cultivars, Novada (resistant to races 1 and 2 ofFusarium oxysporum f.sp.dianthi), Elsy (susceptible to race 1), Lena (susceptible to race 2) and Sam's Pride (susceptible to both races), were selfed and crossed. When three months old, the seedlings were inoculated via the roots or via the stems, after which wilting was recorded weekly according to a 5-point ordinal scale.Analyses were carried out on the proportions of diseased plants. For race 1 variation between the progenies could be described by means of general combining abilities only; GCA values were not affected by the inoculation method used. Also for race 2 GCAs were most important but the GCA values appeared different for the two inoculation methods. It is concluded that resistance to both races is inherited in an additive way.Indications for independently inherited root-specific resistance components (extravascular resistance) were only found with race 2. With both races, the ability to confine the pathogen at the infection site appeared the most important resistance component. Resistant progenies were also characterized by longer latent periods and lower wilting rates.Both race 1 and race 2 induced the accumulation of the phytoalexins dianthalexin and methoxydianthramide S, but race 2 induced higher amounts than race 1. The accumulation of phytoalexins was positively correlated to the resistance level of the progenies against the respective races. The progenies of the double-resistant cultivar Novada appeared to produce particularly high levels of phytoalexins.     

Pathogenicity and vegetative compatibility grouping among Indian populations of Fusarium oxysporum f. sp. ciceris causing chickpea wilt

Thirty-nine isolates of Fusarium oxysporum f. sp. ciceri – the causal agent of chickpea (Cicer arietinum) wilt – collected from different parts of India and representing eight races of the pathogen, were analyzed for virulence and classified on the basis of vegetative compatibility grouping (VCG). The wilt incidence ranged from 24% to 100% on a highly susceptible cultivar JG 62. Six isolates, from Delhi, Gujarat, Karnataka, Punjab and Rajasthan and belonging to six different races of the pathogen, caused 100% wilt incidence. Five isolates belonging to four different races, namely, Foc 143 from Andhra Pradesh, Foc 161 from Chhattisgarh, Foc 146 from Karnataka, Foc 158 from Madhya Pradesh and Foc 50 from Rajasthan, caused low wilt incidence. For VCG analysis, nitrate non-utilizing mutants (nit) were obtained by culturing wild-type isolates on 2.5% potassium chlorate and selecting resistant sectors. Complementary nit mutants were paired in all possible combinations to determine varying degrees of heterokaryon formation within the isolates, which showed that most of the isolates were self-compatible. Pairing of all the mutants showed that the isolates included in the present study belonged to a single VCG (0280). Thus, in spite of variability in the virulence, the Indian populations of the pathogen have only one VCG.     

Phylogenetic relationships of Fusarium oxysporum f. sp. melonis in Iran

Fusarium wilt of melon caused by Fusarium oxysporum f. sp. melonis is a destructive fungal disease in melon growing regions. Isolates of F. oxysporum obtained from six major melon producing provinces in Iran, from melons and other hosts, were characterized based on pathogenicity to melon, vegetative compatibility groups (VCGs) and nuclear ribosomal DNA intergenic spacer (IGS) sequencing. Thirty-four of 41 isolates from Iran in this study were identified as race 1,2 which belonged to either VCG 0134 or an unassigned VCG, which based on IGS sequencing grouped with the VCG 0135 tester isolate. The seven remaining isolates were identified as nonpathogenic to melon belonging to two undescribed VCGs. Based on sequence analyses of the IGS region of Iranian and foreign isolates, nine lineages were identified, each including one VCG. The separation of VCGs into distinct lineages based on IGS sequences is mostly consistent with Repetitive extragenic palindromic PCR (Rep-PCR) results. Exceptions are VCGs 0130 and 0131, which could be differentiated with IGS sequences, but not with Rep-PCR. Different races from the USA, France and Iran associated with VCG 0134 grouped into one IGS lineage but could be differentiated with Rep-PCR, suggesting that this VCG is more diverse than previously thought. Given the long history of melon cultivation in Iran and the Rep-PCR diversity of isolates belonging to this VCG, it could be speculated that VCG 0134 perhaps evolved in Iran.     

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.     

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.