Genetic Variation Among Vegetative Compatibility Groups of Fusarium oxysporum f. sp. cubense Analyzed by DNA Fingerprinting

ABSTRACT Genetic variation within a worldwide collection of 208 isolates of Fu-sarium oxysporum f. sp. cubense, representing physiological races 1, 2, 3, and 4 and the 20 reported vegetative compatibility groups (VCGs), was analyzed using modified DNA amplification fingerprinting. Also characterized were 133 isolates that did not belong to any of the reported VCGs of F. oxysporum f. sp. cubense including race 3 isolates from a Heliconia species and isolates from a symptomatic wild banana species growing in the jungle in peninsular Malaysia. The DNA fingerprint patterns were generally VCG specific, irrespective of geographic or host origin. A total of 33 different genotypes were identified within F. oxysporum f. sp. cu-bense; 19 genotypes were distinguished among the isolates that belonged to the 20 reported VCGs, and 14 new genotypes were identified among the isolates that did not belong to any of the existing VCGs. DNA fingerprinting analysis also allowed differentiation of nine clonal lineages within F. oxysporum f. sp. cubense. Five of these lineages each contained numerous closely related VCGs and genotypes, and the remaining four lineages each contained a single genotype. The genetic diversity and geographic distribution of several of these lineages of F. oxysporum f. sp. cubense suggests that they have coevolved with edible bananas and their wild diploid progenitors in Asia. DNA fingerprinting analysis of isolates from the wild pathosystem provides further evidence for the coevolution hypothesis. The genetic isolation and limited geographic distribution of four of the lineages of F. oxysporum f. sp. cubense suggests that the pathogen has also arisen independently, both within and outside of the center of origin of the host.     

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.     

Physiological Races and Vegetative Compatibility Groups of Fusarium oxysporum f. sp. lactucae Isolated from Crisphead Lettuce in Japan

One hundred and sixteen isolates of Fusarium oxysporum f. sp. lactucae obtained from 85 fields in three crisphead lettuce-producing areas in Nagano Prefecture, Japan were typed for races using differential cultivars Patriot, Banchu Red Fire and Costa Rica No. 4. They were also grouped into vegetative compatibility groups (VCGs) using complementation tests with nitrate non-utilizing (nit) mutants. Two California strains reported as F. oxysporum f. sp. lactucum, a type culture of F. oxysporum f. sp. lactucae, and 28 avirulent isolates of F. oxysporum obtained from crisphead lettuce were included for comparison. Among Nagano isolates, 66 isolates were identified as race 1, and 50 as race 2. Race 1 strains derived from Shiojiri and Komoro cities and race 2 from Kawakami village and Komoro city. All isolates of race 2 were biotin auxotrophs, and the race could be distinguished based on its requirement for biotin on minimal nitrate agar medium (MM). Pathogenic isolates were classified into two VCGs and three heterokaryon self-incompatible isolates. Strong correlations were found between race and VCG. All the race 1 strains were assigned to VCG 1 except self-incompatible isolates, and all the race 2 strains to VCG 2. The 28 avirulent isolates of F. oxysporum were incompatible with VCG 1 and VCG 2. California strains was vegetatively compatible with VCG 1, and they were assigned to race 1. Based on vegetative compatibility, these two races of F. oxysporum f. sp. lactucae may be genetically distinct, and F. oxysporum f. sp. lactucae race 1 is identical to F. oxysporum f. sp. lactucum. Received 7 May 2002/ Accepted in revised form 6 September 2002     

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.     

串珠镰刀菌孢子表面的一种凝集素

 用0.2% SDS磷酸缓冲液从串珠镰刀菌(Fusarium moniliforme)孢子表面抽提蛋白质。孢子表面蛋白经DEAE-Sepharose阴离子交换柱层析和Sephacryl S-100分子筛柱层析,分离和纯化了一种凝集素。该凝集素的分子量为70 kDa,糖含量为19.8%,对兔血红细胞有很强的凝集活性,凝集活性被半乳糖特异性地抑制。EDTA和一些金属离子不影响凝集活性。     

Vegetative compatibility of Fusarium oxysporum from sweet basil in Israel

Fusarium wilt and crown rot of sweet basil, caused by Fusarium oxysporum f.sp. basilici (F.o.ba.), is widespread in Israel. Affected plants show a variety of symptoms, including vascular wilt as well as crown rot, and masses of macroconidia on stem surfaces. We used vegetative compatibility to determine whether F.o.ba. isolates associated with various symptoms and sources are genetically related. All 119 isolates previously described as F.o.ba., and 42 additional F. oxysporum isolates which had not been tested for pathogenicity, belonged to a single vegetative compatibility group (VCG). The various symptoms are therefore induced by a single pathogenic form which appears to be a specific clone of F. oxysporum. The isolates of F.o.ba. from Israel were vegetatively compatible with eight isolates of F.o.ba. from Italy and the USA, but not with nonpathogenic isolates of F. oxysporum from basil, or with F.o. lycopersici or F.o. radicis-lycopersici from tomato. We conclude that the population of F.o.ba. in Israel belongs to the common VCG of this pathogen described in the USA, and which includes American and Italian isolates.     

Genetic Diversity of Fusarium oxysporum Isolates from Cucumber: Differentiation by Pathogenicity, Vegetative Compatibility, and RAPD Fingerprinting

ABSTRACT A total of 106 isolates of Fusarium oxysporum obtained from diseased cucumber plants showing typical root and stem rot or Fusarium wilt symptoms were characterized by pathogenicity, vegetative compatibility, and random amplified polymorphic DNA (RAPD). Twelve isolates of other formae speciales and races of F. oxysporum from cucurbit hosts, three avirulent isolates of F. oxysporum, and four isolates of Fusarium spp. obtained from cucumber were included for comparison. Of the 106 isolates of F. oxysporum from cucumber, 68 were identified by pathogenicity as F. oxysporum f. sp. radicis-cucumerinum, 32 as F. oxysporum f. sp. cucumerinum, and 6 were avirulent on cucumber. Isolates of F. oxysporum f. sp. radicis-cucumerinum were vegetatively incompatible with F. oxysporum f. sp. cucumerinum and the other Fusarium isolates tested. A total of 60 isolates of F. oxysporum f. sp. radicis-cucumerinum was assigned to vegetative compatibility group (VCG) 0260 and 5 to VCG 0261, while 3 were vegetatively compatible with isolates in both VCGs 0260 and 0261 (bridging isolates). All 68 isolates of F. oxysporum f. sp. radicis-cucumerinum belonged to a single RAPD group. A total of 32 isolates of F. oxysporum f. sp. cucumerinum was assigned to eight different VCGs and two different RAPD groups, while 2 isolates were vegetatively self-incompatible. Pathogenicity, vegetative compatibility, and RAPD were effective in distinguishing isolates of F. oxysporum f. sp. radicis-cucumerinum from those of F. oxysporum f. sp. cucumerinum. Parsimony and bootstrap analysis of the RAPD data placed each of the two formae speciales into a different phylogenetic branch.     

Characterization of a Regional Population of Fusarium oxysporum f. sp. niveum by Race, Cross Pathogenicity, and Vegetative Compatibility

ABSTRACT Eighty-eight isolates of Fusarium oxysporum f. sp. niveum, collected from wilted watermelon plants and infested soil in Maryland and Dela-ware, were characterized by cross pathogenicity to muskmelon, race, and vegetative compatibility. Four isolates (4.5%) were moderately pathogenic to >/=2 of 18 muskmelon cultivars in a greenhouse test, and one representative isolate also was slightly pathogenic in field microplots. The four isolates all were designated as race 2, and were in vegetative compatibility group (VCG) 0082. Of the 74 isolates to which a VCG could be assigned, 41 were in VCG 0080, the VCG distributed most widely; 27 were in VCG 0082, and were distributed in half of the 20 watermelon fields surveyed; and 6 were in the newly described VCG 0083, and were restricted to three fields. Among the isolates in VCG 0080, 8 were designated as race 0, 21 as race 1, and 12 as race 2. Of the isolates in VCG 0082, 6 were designated as race 0, 11 as race 1, and 10 as race 2. All isolates in VCG 0083 were designated as race 2. Isolates from more than one race within the same VCG or isolates from more than one VCG were recovered from single plants and fields. No differences in aggressiveness on differential watermelon cultivars were observed among isolates from different VCGs of the same race. A diverse association between virulence and VCG throughout the Mid-Atlantic region suggests that the pathotypes of F. oxysporum f. sp. niveum may be of local origin or at least long existent in the region.     

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.     

瓜类尖孢镰刀菌的营养体亲和群研究

 应用营养亲和性方法研究了尖孢镰刀菌菌株抗氯酸盐突变体和nit突变体的诱发规律及分布特性,以及菌株营养体亲和群(VCG)的划分。研究表明,不同寄主(黄瓜、甜瓜和西瓜)分离的尖孢镰刀菌菌株形成的抗氯酸盐突变体数目差异不显著,平均为每个接种点产生0.89~0.98个;但寄主不同部位(根部、茎基部和茎中部)分离的菌株间差异显著,形成的数目分别为1.27、0.75及0.76个。菌株产生的nit1突变体比例(75.40%)显著高于nitM突变体比例(13.17%);nit1突变体数目会因菌株的寄主及菌株寄主部位的不同而有差异,寄主为黄瓜、甜瓜和西瓜的菌株产生的比例依次为67.73%、83.71%和77.50%,根部、茎基部及茎中部分离菌株产生的比例依次为81.82%、78.48%和68.64%,而在致病菌株与非致病菌株间无显著差异,分别为74.43%和79.63%;nitM突变体数目受菌株寄主影响较小,所占比例在11.17%~13.92%之间;而在寄主不同部位分离的菌株及致病菌株与非致病菌株间差异显著,分离自茎基部的菌株所占比例最高为15.97%,茎中部菌株所占比例最低为9.87%,致病菌株与非致病菌株所占比例分别为14.08%和9.26%。供试菌株分为7个VCGs,其特点为来源于不同寄主的尖孢镰刀菌菌株互不亲和,同一寄主的致病菌株与非致病菌株均不亲和,同一寄主不同部位分离的菌株可亲和。     

Vegetative Compatibility Groups in Colletotrichum coccodes, the Causal Agent of Black Dot on Potato

ABSTRACT Black dot of potato, caused by Colletotrichum coccodes, is a disease of growing economic importance, but the degree of genetic diversity and pathogenic differentiation among isolates is unknown. Using nitrate auxotrophic (Nit) mutants, we characterized vegetative compatibility groups (VCG) diversity for C. coccodes for 110 isolates originating from Israel, The Netherlands, and France. We recovered frequencies of nit1 and NitM mutant classes at 38.5 and 7.2%, respectively, and selected 12 isolates as tester isolates. Using these testers, we defined four multimember VCGs at 7.3, 35.5, 20.0, and 10.0% frequency in this sample. Thirty isolates (27.3% of all tested isolates) could not be assigned to any of the major groups, and showed only self-compatibility. The frequency of recovery of Nit mutant sectors was highest in isolates from VCG4, with 50.9 and 13.6% recovery for nit1 and NitM, respectively. However, we did not detect differences in the frequency of mutant classes among the three countries of origin. In pathogenicity tests, isolates from VCG3 were the most aggressive to potato, as expressed by high stem colonization levels and sclerotia density on root and crown. These results suggest that there is significant VCG diversity in this species and that this VCG diversity may be correlated with pathogenic characteristics or specialization.     

Differential Colonization of Tomato Roots by Nonpathogenic and Pathogenic Fusarium oxysporum Strains May Influence Fusarium Wilt Control

ABSTRACT Histochemical staining, beta-glucuronidase (GUS) activity, or placing roots on agar were methods used to characterize interactions between the pathogenic fungus, Fusarium oxysporum f. sp. lycopersici, and the nonpathogenic biocontrol F. oxysporum strain 70T01 with respect to colonization behaviors, interaction sites, and population densities on tomato roots. Mycelia of strain 70T01, a genetic transformant expressing stable GUS activity, hygromycin B resistance, and effective disease control, were localized in epidermal and cortex cell layers of tomato roots in a discontinuous and uneven pattern. In contrast, mycelia of F. oxysporum f. sp. lycopersici were found in the vascular bundles. Thus, direct interactions between the two fungi likely happen in the root surface cell layers. Colonization density of strain 70T01 was related to the inoculation density but decreased with distance from the inoculation site. Host defense reactions, including increased cell wall thickness or papilla deposits, were adjacent to 70T01 hyphae. Experiments done in soil showed that strain 70T01 densities in roots were highest at inoculation zones and barely detectable for root segments more than 2 cm away from the inoculation sites. F. oxysporum f. sp. lycopersici densities were lowest at 70T01 inoculation zones and highest (>10 times) where strain 70T01 was not directly applied. Newly elongating roots where strain 70T01 did not reach were available for infection by the pathogen. The higher strain 70T01 density was always found when the plants were simultaneously infected by F. oxysporum f. sp. lycopersici, suggesting that F. oxysporum f. sp. lycopersici has as much influence in predisposing the plant to colonization by strain 70T01 as strain 70T01 has on providing disease protection against the pathogen.     

Vegetative compatibility and heterokaryon stability in Fusarium oxysporum f.sp. radicis-lycopersici from Italy

Fusarium crown and root rot, caused by Fusarium oxysporum f.sp. radicis-lycopersici ( Forl ), is one of the most destructive soilborne diseases of tomato in Italy. Chlorate-resistant, nitrate-nonutilizing ( nit ) mutants were used to determine vegetative compatibility among 191 isolates of Forl collected in five geographic regions (Calabria, Emilia-Romagna, Liguria, Sardinia, Sicily) in Italy. The isolates were assigned to five vegetative compatibility groups (VCGs): 65 isolates to VCG 0090; 99 to VCG 0091; 23 to VCG 0092; two to VCG 0093; and two to VCG 0096. The population structure of Forl in Italy is similar to that reported for Israel, and differs from that found in North Atlantic European countries, where VCG 0094 is predominant. The stability of prototrophic heterokaryons originating from hyphal anastomosis between compatible complementary nit mutants was assessed through conidial analysis and mycelial mass transfer. Most monoconidial cultures (84%) recovered from 117 prototrophic heterokaryons were nit mutants, indicating that heterokaryons generally do not proliferate well through conidiation; most of the 177 prototrophic heterokaryons examined were unstable, and only 9% sustained prototrophic growth through the tenth mycelial transfer upon subculturing. The prototrophic growth is proposed to be maintained through restoration of the heterokaryotic state by continual anastomosis between adjacent homokaryotic hyphae. Since heterokaryosis is a prerequisite for parasexual recombination, we speculate that this mechanism is unlikely to play a major role in generating the VCG diversity found among Forl or other strains of F. oxysporum.     

Pathogenic and Genetic Variation in the Japanese Strains of Fusarium oxysporum f. sp. melonis

ABSTRACT Pathogenic variation among 41 Japanese strains of Fusarium oxysporum f. sp. melonis was analyzed by pathogenicity tests with muskmelon, oriental melon, and oriental pickling melon cultivars. Based on pathogenicity to muskmelon cvs. Amus and Ohi and oriental melon cv. Ogon 9, 41 strains were divided into 3 groups that corresponded completely to Risser's races 0, 2, and 1,2y. To further characterize pathogenic variation within the forma specialis and races, strains were assayed for pathogenicity to 42 additional muskmelon, oriental melon, and oriental pickling melon cultivars. All strains of race 1,2y were pathogenic to all cultivars tested. Strains of race 0 were divided into six variants based on differences in pathogenicity to three muskmelon cultivars; strains of race 2 also were classified into six variants based on differences in pathogenicity to two muskmelon cultivars and one oriental melon cultivar. Genetic variation among strains was analyzed by DNA fingerprinting with four repetitive DNA sequences: FOLR1 to FOLR4. Thirty-six fingerprint types were detected among forty-one strains by pooling results of fingerprinting with four probes. Cluster analysis showed distinct genetic groups correlated with races: the fingerprint types detected in each of races 2 and 1,2y were grouped into a single cluster, and two distinct genetic groups were found in race 0. However, pathogenic variation detected within races 0 and 2 could not be differentiated based on the nuclear markers examined.     

Vegetative Compatibility of Fusarium graminearum Isolates and Genetic Study on Their Carbendazim-Resistance Recombination in China

ABSTRACT Monoconidial isolates of 33 carbendazim-sensitive isolates and 31 carbendazim-resistant isolates of Fusarium graminearum were selected from three regions of China for vegetative compatibility group (VCG) analysis. A total of 213 and 224 nit mutants were recovered from the 33 sensitive and the 31 resistant isolates, respectively. Of all the nit mutants, the frequency of the different phenotypes was 44.6, 46.5, 5.7, and 3.2% for nit1, nit3, nitM, and nitA, respectively. VCG analysis identified 30 different VCGs among the 33 sensitive- and the 31 carbendazim-resistant isolates, with VCG diversity 0.91 and 0.97, respectively. Both, a carbendazim-sensitive and a -resistant isolate from the same field belonged to the same VCG. In all then, a total of 59 VCGs were identified among the 64 isolates with an overall VCG diversity 0.92. Direct hyphal fusion was observed in six pairs of vegetatively compatible complements, which is evidence of heterokaryon formation. It was hypothesized that carbendazim resistance could not be transferred by hyphal fusion or there is a small chance to be transferred between two compatible isolates. Three stable sexual recombinants of F. graminearum were randomly chosen from each of the three genetic crosses to study their biological properties. There were no significant differences in mycelial linear growth and pathogenicity between recombinants and their parents, but they differ in sporulation ability and capacity to produce perithecia. We concluded that sexual recombination presumably played a role in the development of carbendazim resistance under field conditions.     

Pathogenic, Genetic and Molecular Characterisation of Fusarium oxysporum f.sp. lilii

Isolates of Fusarium oxysporum from lily were screened for pathogenicity, vegetative compatibility and DNA restriction fragment length polymorphisms, and compared to reference isolates of F. oxysporum f.sp. gladioli and F. oxysporum f.sp. tulipae to justify the distinction of F. oxysporum f.sp. lilii. Twenty-four isolates from different locations in The Netherlands (18 isolates), Italy (4 isolates), Poland and the United States (1 isolate each) shared unique RFLP patterns with probes D4 and pFOM7, while hybridization did not occur with a third probe (F9). Except for a self-incompatible isolate, these 24 isolates all belonged to a single vegetative compatibility group (VCG 0190). Isolates belonging to VCG 0190 were highly pathogenic to lily, but not to gladiolus or tulip, except for a single nonpathogenic isolate. Six saprophytic isolates of F. oxysporum from lily were nonpathogenic or only slightly aggressive to lily, gladiolus and tulip, belonged to unique VCGs and had distinct RFLP patterns. Three pathogenic isolates previously considered to belong to F. oxysporum f.sp. lilii were identified as F. proliferatum var. minus; all three belonged to the same VCG and shared unique RFLP patterns. These three isolates were moderately pathogenic to lily and nonpathogenic to gladiolus and tulip. The reference isolates of F. oxysporum f.sp. tulipae were pathogenic to tulip, but not to lily and gladiolus; they shared a distinct RFLP pattern, different from those encountered among pathogenic and saprophytic isolates from lily, and formed a separate new VCG (VCG 0230). Reference isolates of F. oxysporum f.sp. gladioli belonging to VCG 0340 proved pathogenic to both gladiolus and lily, but not to tulip. These isolates, as well as isolates belonging to VCGs 0341, 0342 and 0343 of F. oxysporum f.sp. gladioli, had RFLP patterns different from those encountered among the isolates from lily or tulip. These findings identify F. oxysporum f.sp. lilii as a single clonal lineage, distinct from F. oxysporum f.sp. gladioli and f.sp. tulipae.     

Vegetative Compatibility Groups of Verticillium dahliae in Israel: Their Distribution and Association with Pathogenicity

A collection of 565 isolates of Verticillium dahliae, recovered between 1992 and 1997 from 13 host plant species and soil at 47 sites in Israel, was tested for vegetative compatibility using nitrate-nonutilizing (nit) mutants. Three vegetative compatibility groups (VCGs) were found and identified as VCG2A (28 isolates), VCG2B (158 isolates), and VCG4B (378 isolates) by using international reference strains. One isolate was heterokaryon self-incompatible. Of the VCG2B isolates, 92% were recovered from the northern part of Israel and 90% of VCG4B isolates were recovered from the south, with some overlap in the central region. Isolates of the minor group VCG2A were geographically scattered among the two major VCGs. Isolates of the same VCG resembled one another more than isolates from different VCGs based on colony and microsclerotial morphology, temperature responses, and, partially, pathogenicity. Different pathotypes were defined among 60 isolates tested, using cotton (cv. Acala SJ-2) and eggplant (cv. Black Beauty) as differentials. All isolates in VCG2A and 86% of the isolates in VCG4B, irrespective of their origin, induced weak to moderate symptoms on cotton and moderate to severe symptoms on eggplant and were similar to the previously described cotton nondefoliating patho-type. In contrast, all cotton isolates in VCG2B caused severe foliar symptoms, stunting, and often death, but little or no defoliation of inoculated cotton plants. These were defined as a cotton defoliating-like pathotype and induced only weak to moderate symptoms on eggplant. We concluded that vegetative compatibility grouping of V. dahliae in Israel is closely associated with specific pathogenicity and other phenotypic traits.     

利用RAPD-STS和实时定量PCR鉴别菠菜枯萎病病原菌(Fusarium oxysporum f.sp.spinaciae)

 菠菜枯萎病是由致病性镰刀菌(F.o.f.sp.spinaciae)引起的,是菠菜生产中的重要病害之一。利用常规方法鉴定菠菜枯萎病病原菌需耗费大量时间,并且很难得到正确的结论。随机扩增多态性DNA序列标签(Randomly amplified polymorphic DNA-sequence tagged sites,RAPD-STS)为病原菌鉴定提供了一种有效方法。本研究通过对供试菌株的RAPD分析,克隆出了1个菠菜枯萎病病原菌的特异片段(GenBank登录号:AY337463)。根据测序结果设计了1对菠菜枯萎病病原菌的特异引物,并利用常规PCR和实时定量PCR(real-time PCR)2种方法对病原菌进行了鉴定,并对2种方法的敏感性进行了比较。结果表明,2种PCR方法都可以鉴定菠菜枯萎病病原菌(F.o.f.sp.spinaciae),但二者对病原菌DNA敏感程度不同,常规PCR检测的最低DNA量100Pg,而实时定量PCR检测的最低DNA量是1pg。同时,实时定量PCR还可以对病原菌DNA进行定量分析,并依此估算病原菌的数量。该方法可用于菠菜枯萎病病原菌的快速鉴定和病因诊断。     

Genetic Diversity of Pathogenic and Nonpathogenic Populations of Fusarium oxysporum Isolated from Carnation Fields in Argentina

ABSTRACT In order to elucidate the origin of Fusarium oxysporum f. sp. dianthi in Argentina, the genetic diversity among pathogenic isolates together with co-occurring nonpathogenic isolates on carnation was investigated. In all, 151 isolates of F. oxysporum were obtained from soils and carnation plants from several horticultural farms in Argentina. The isolates were characterized using vegetative compatibility group (VCG), intergenic spacer (IGS) typing, and pathogenicity tests on carnation. Seven reference strains of F. oxysporum f. sp. dianthi also were analyzed and assigned to six different IGS types and six VCGs. Twenty-two Argentinean isolates were pathogenic on carnation, had the same IGS type (50), and belonged to a single VCG (0021). The 129 remaining isolates were nonpathogenic on carnation and sorted into 23 IGS types and 97 VCGs. The same VCG never occurred in different IGS types. Our results suggest that the pathogen did not originate in the local populations of F. oxysporum but, rather, that it was introduced into Argentina. Given the genetic homogeneity within Argentinean isolates of F. oxysporum f. sp. dianthi, either IGS type or VCG can be used for the identification of the forma specialis dianthi currently in Argentina.