A two-locus DNA sequence database for typing plant and human pathogens within the Fusarium oxysporum species complex

We constructed a two-locus database, comprising partial translation elongation factor (EF-1alpha) gene sequences and nearly full-length sequences of the nuclear ribosomal intergenic spacer region (IGS rDNA) for 850 isolates spanning the phylogenetic breadth of the Fusarium oxysporum species complex (FOSC). Of the 850 isolates typed, 101 EF-1alpha, 203 IGS rDNA, and 256 two-locus sequence types (STs) were differentiated. Analysis of the combined dataset suggests that two-thirds of the STs might be associated with a single host plant. This analysis also revealed that the 26 STs associated with human mycoses were genetically diverse, including several which appear to be nosocomial in origin. A congruence analysis, comparing partial EF-1alpha and IGS rDNA bootstrap consensus, identified a significant number of conflicting relationships dispersed throughout the bipartitions, suggesting that some of the IGS rDNA sequences may be non-orthologous. We also evaluated enniatin, fumonisin and moniliformin mycotoxin production in vitro within a phylogenetic framework.

Generation of recombinant alpaca VHH antibody fragments for the detection of the mycotoxin ochratoxin A

To develop sensor technologies based on genetically engineered recognition elements, recombinant antibodies characterised by high stability are a prerequisite. Here we describe the first successful isolation of recombinant alpaca single-domain antibody fragments with high affinity to the mycotoxin ochratoxin A (OTA). Variable domains (VHH) of heavy-chain antibodies binding to OTA were cloned from an immunised alpaca. Selected VHH clones clustered in four major groups, based on protein sequence similarity. Six representative VHH antibody fragments were produced in Escherichia coli and characterised for their sensitivity and specificity by indirect competitive enzyme-linked immunosorbent assays. OTA concentrations causing 50% inhibition (IC50) ranged from 12 ng/ml for antibody fragment OCH-62 to 442 ng/ml for antibody fragment OCH-40. The IC50 of OCH-62 for ochratoxin B, an OTA analogue, was 476 ng/ml. No significant cross-reactivity was observed with common food constituents with structural similarities with parts of OTA, such as L-phenylalanine and coumarin. The performance of OCH-62 for detection of OTA in food matrices was comparable to the performance in buffer (white wine: IC50=17 ng/ml; red wine: IC50=21 ng/ml; instant coffee: IC50=17 ng/ml). In a membrane-based flow-through immunoassay, used for fast visual screening of samples, OCH-62 showed a cut-off level of 10 ng/ml OTA. Thereby, OCH-62 ranked among the best recombinant antibody fragments described for mycotoxins and is an excellent candidate for the design of food contamination sensors based on nanotechnology.

Large-scale gene discovery in the septoria tritici blotch fungus Mycosphaerella graminicola with a focus on in planta expression

The foliar disease septoria tritici blotch, caused by the fungus Mycosphaerella graminicola, is currently the most important wheat disease in Europe. Gene expression was examined under highly different conditions, using 10 expressed sequence tag libraries generated from M. graminicola isolate IPO323 using seven in vitro and three in planta growth conditions. To identify fungal clones in the interaction libraries, we developed a selection method based on hybridization with the entire genomic DNA of M. graminicola, to selectively enrich these libraries for fungal genes. Assembly of the 27,007 expressed sequence tags resulted in 9,190 unigenes, representing 5.2 Mb of the estimated 39-Mb genome size of M. graminicola. All libraries contributed significantly to the number of unigenes, especially the in planta libraries representing different stages of pathogenesis, which covered 15% of the library-specific unigenes. Even under presymptomatic conditions (5 days postinoculation), when fungal biomass is less than 5%, this method enabled us to efficiently capture fungal genes expressed during pathogenesis. Many of these genes were uniquely expressed in planta, indicating that in planta gene expression significantly differed from in vitro expression. Examples of gene discovery included a number of cell wall-degrading enzymes, a broad set of genes involved in signal transduction (n=11) and a range of ATP-binding cassette (n=20) and major facilitator superfamily transporter genes (n=12) potentially involved in protection against antifungal compounds or the secretion of pathogenicity factors. In addition, evidence is provided for a mycovirus in M. graminicola that is highly expressed under various stress conditions, in particular, under nitrogen starvation. Our analyses provide a unique window on in vitro and in planta gene expression of M. graminicola.

Fusarium populations on Chinese barley show a dramatic gradient in mycotoxin profiles

We report on a large gene bank of Fusarium isolates established by a broad survey conducted in 2005 in which infected barley ears were collected in 23 counties of seven provinces and two municipalities along the Yangtze River in China. In total, 1,894 single spore isolates were obtained. The isolates were characterized at the species level by a newly developed and robust set of diagnostic primers based on single nucleotide polymorphisms (SNPs) among members of the F. graminearum clade. In addition, we determined their chemotype using previously described polymerase chain reaction (PCR) primers. The results showed that in all regions F. asiaticum was the predominant species causing Fusarium head blight (FHB) on barley in China (N = 1,706), while in the upper valleys of the Yangtze River also F. graminearum sensu stricto, F. meridionale, and F. proliferatum were found. Major differences in the chemotypes were found in the F. asiaticum populations, from very high to exclusive nivalenol (NIV) chemotypes in the mountainous upper valleys of the Yangtze River to predominantly deoxynivalenol (DON) chemotypes in the middle and lower valleys. In contrast to the F. asiaticum isolates from three counties in Sichuan province, which were largely NIV producers (278 of 291), F. graminearum isolates from these sampling sites were for the vast majority (27 of 28) DON producers, indicating that despite sharing the same habitat, these sympatric species apparently have unique mycotoxin chemotypes.

Quantitative detection of Fusarium spp. and its correlation with fumonisin content in maize from South African subsistence farmers

A quantitative detection tool was developed to enable the monitoring of fumonisin-producing fungi in food and feed commodities. To this end, a quantitative PCR (TaqMan) was developed that targets a conserved region in the polyketide synthase gene fum1, which is involved in the biosynthesis of fumonisin. Hence, this method specifically detected isolates from the fumonisin-producing species Fusarium verticillioides, F. proliferatum, F. nygamai and F. globosum whereas isolates of the fumonisin non-producing species F. equiseti, F. graminearum, F. oxysporum, F. semitectum and F. subglutinans that commonly occur on maize were not detected. Moreover, a few fumonisin non-producing F. verticillioides isolates did not generate any fluorescent signals and were therefore not detected. The correlation between quantitative PCR and mycotoxin content was determined using field samples collected at homestead farms in South Africa. Among 40 samples from the Eastern Cape collected in 2005 a good correlation (R2=0.8303) was found between pg fungal DNA and fumonisin content. A similar correlation (R2=0.8658) was found among 126 samples collected from four provinces in South Africa in 2007. These observations indicate that samples containing ≥ 40 pg fungal DNA/mg sample are suspected of also exceeding the 1 mg/kg total fumonisin level and therefore do not comply with the European Commission limit for fumonisins B1+B2 for maize intended for direct human consumption that applies from 1 October 2007. Combined with the very high maize intake, our results indicate that fumonisin levels in maize from South African homesteads regularly exceed the tolerable daily intake for fumonisins.

The Fusarium graminearum genome reveals a link between localized polymorphism and pathogen specialization

We sequenced and annotated the genome of the filamentous fungus Fusarium graminearum, a major pathogen of cultivated cereals. Very few repetitive sequences were detected, and the process of repeat-induced point mutation, in which duplicated sequences are subject to extensive mutation, may partially account for the reduced repeat content and apparent low number of paralogous (ancestrally duplicated) genes. A second strain of F. graminearum contained more than 10,000 single-nucleotide polymorphisms, which were frequently located near telomeres and within other discrete chromosomal segments. Many highly polymorphic regions contained sets of genes implicated in plant-fungus interactions and were unusually divergent, with higher rates of recombination. These regions of genome innovation may result from selection due to interactions of F. graminearum with its plant hosts.

Molecular diagnostics for the sigatoka disease complex of banana

ABSTRACT The Sigatoka disease complex of banana involves three related ascomycetous fungi, Mycosphaerella fijiensis, M. musicola, and M. eumusae. The exact distribution of these three species and their disease epidemiology remain unclear, because their symptoms and life cycles are rather similar. Disease diagnosis in the Mycosphaerella complex of banana is based on the presence of host symptoms and fungal fruiting structures, which hamper preventive management strategies. In the present study, we have developed rapid and robust species-specific molecular-based diagnostic tools for detection and quantification of M. fijiensis, M. musicola, and M. eumusae. Conventional species-specific polymerase chain reaction (PCR) primers were developed based on the actin gene that detected DNA at as little as 100, 1, and 10 pg/mul from M. fijiensis, M. musicola, and M. eumusae, respectively. Furthermore, TaqMan real-time quantitative PCR assays were developed based on the beta-tubulin gene and detected quantities of DNA as low as 1 pg/mul for each Mycosphaerella sp. from pure cultures and DNA at 1.6 pg/mul per milligram of dry leaf tissue for M. fijiensis that was validated using naturally infected banana leaves.

Population Dynamics of Fusarium spp. and Microdochium nivale in Crops and Crop Residues of Winter Wheat

ABSTRACT Naturally occurring populations of Fusarium avenaceum, F. culmorum, F. graminearum, F. poae, and Microdochium nivale were studied in two field experiments from anthesis in June 2003 until harvest in crops of winter wheat, and subsequently during 10 months after harvest until June 2004 on their residues exposed on the soil surface under field conditions. The dynamics of the different pathogens were estimated by quantifying the amount of DNA present in wheat tissues using TaqMan-polymerase chain reaction. While colonization of grain by Fusarium spp. and M. nivale was low, high amounts of DNA of F. avenaceum, F. graminearum, and F. culmorum were found in ear residues, internodes, and nodes of the mature crop. Amounts of DNA of pathogens decreased significantly during the following 10 months in residues of internodes and nodes, but not in residues of stem bases. Knowledge on population dynamics of pathogens will help to develop preventive measures aimed at reduction of inoculum sources of head blight pathogens.

Isolation and characterization of the mating type locus of Mycosphaerella fijiensis, the causal agent of black leaf streak disease of banana

SUMMARY Idiomorphs mat1-1 and mat1-2 from Mycosphaerella fijiensis, the causal agent of black leaf streak disease of banana, were isolated. Degenerate oligos were used to amplify the HMG box of the mat1-2 idiomorph from M. fijiensis, showing homology with the HMG box of Mycosphaerella graminicola. Using a DNA walking strategy, anchored on the DNA lyase gene towards the HMG box, a 9-kb-long region of mat1-2 was obtained. A 5-kb fragment from the mat1-1 region was obtained by long-range PCR using primers on the flanking regions, which have close to 100% identity between both idiomorphs. High-identity (77-89%), inverted regions within both idiomorphs were found, which suggest unique inversion events, which have not been found before, and that could have been significant in the evolution of this species. The predicted genes showed the conserved introns in both idiomorphs as well as an additional intron within the alpha box. The implications for the evolution of species in the Mycosphaerella complex on banana are discussed.

Discovery of a functional Mycosphaerella teleomorph in the presumed asexual barley pathogen Septoria passerinii

We studied the possibility of a teleomorph associated with the genotypically diverse septoria speckled leaf blotch (SSLB) pathogen of barley, Septoria passerinii. A teleomorph in the genus Mycosphaerella had been predicted previously based on phylogenetic analyses. This prediction was tested with experiments in the Netherlands and the United States by co-inoculating isolates with opposite mating types onto susceptible barley cultivars and monitoring leaves for sexual structures and for the discharge of ascospores. Characterization of putative hybrid progeny by both molecular (AFLP, RAPD, mating type, and ITS sequencing) and phenotypic analyses confirmed that a Mycosphaerella teleomorph of S. passerinii has been discovered approximately 125 years after the description of the anamorph. Progeny had recombinant genotypes of the molecular alleles present in the parents, and the identities of representative progeny isolates as S. passerinii were confirmed by ITS sequencing. A previously unknown sexual cycle explains the high degree of genetic variation among isolates found in nature. The experimental identification of a predicted teleomorph for S. passerinii indicates that cryptic sexual cycles may be common for many other "asexual" fungi with high levels of genotypic diversity.

Tagging target genes of the MAT1-2-1 transcription factor in Fusarium verticillioides (Gibberella fujikuroi MP-A)

Mating type in filamentous ascomycetes is controlled by idiomorphic alleles, named MAT1-1 and MAT1-2, which contain 1-3 genes. Of these genes MAT1-1-1 and MAT1-2-1 encode putative transcription factors and are thus considered to be the major regulators of sexual communication and mating. Fungi with no known sexual stage may also have fully functional mating type genes and therefore it was plausible to hypothesize that the MAT products may also regulate other types of genes not involved directly in the mating process. To identify putative target genes of these transcription factors in Fusarium verticillioides, DeltaMAT1-2-1 knock out mutants were produced and transcript profiles of mutant and wild type were compared by means of differential cDNA hybridization. Clones, either up- or down-regulated in the DeltaMAT1-2-1 mutant were sequenced and a total of 248 sequences were blasted against the NCBI database as well as the Gibberella zeae and Gibberella moniliformis genomes. Fifty-five percent of the clones were down-regulated in the mutant, indicating that the MAT1-2-1 product positively affected these tagged sequences. On the other hand, 45% were found to be up-regulated in the mutant, suggesting that the MAT1-2-1 product also exerted a negative regulatory function on this set of genes. Sequences involved in protein synthesis and metabolism occurred more frequently among the clones up-regulated in the mutant, whereas genes belonging to cell signalling and communication were especially frequently tagged among the sequences down-regulated in the mutant.

The MAP kinase-encoding gene MgFus3 of the non-appressorium phytopathogen Mycosphaerella graminicola is required for penetration and in vitro pycnidia formation

SUMMARY In eukaryotes, a family of serine/threonine protein kinases known as mitogen-activated protein kinases (MAPKs) is involved in the transduction of a variety of extracellular signals and in the regulation of growth and development. We identified a MAPK-encoding gene in Mycosphaerella graminicola strain IPO323 with high homology to the orthologous Fus3 gene of Saccharomyces cerevisiae and designated it MgFus3. Early colony development of the MgFus3 mutants during in vitro growth was similar to those of the wild-type and ectopic controls, but at the later stages of growth MgFus3 mutants did not become melanized, showed altered polarized growth and were unable to produce aerial mycelia. The MgFus3 mutants were non-pathogenic, and detailed microscopic analyses revealed that they failed to colonize the mesophyll tissue owing to the inability to penetrate stomata. Unlike the wild-type strain, MgFus3 mutants were unable to differentiate pycnidia on plant-derived media. Thus, in addition to the crucial role of MgFus3 in the regulation of penetration, it may also be involved in regulating asexual fructification. Hence, MgFus3 can be regarded as a multifunctional pathogenicity factor of M. graminicola.

MgSlt2, a cellular integrity MAP kinase gene of the fungal wheat pathogen Mycosphaerella graminicola, is dispensable for penetration but essential for invasive growth

Among expressed sequence tag libraries of Mycosphaerella graminicola isolate IPO323, we identified a full-length cDNA clone with high homology to the mitogen-activated protein (MAP) kinase Slt2 in Saccharomyces cerevisiae. This MAP kinase consists of a 1242-bp open reading frame, and encodes a 414-amino-acid protein. We designated this homolog MgSlt2, generated MgSlt2 knockout strains in M. graminicola isolate IPO323, and found several altered phenotypes in vitro as well as in planta. In yeast glucose broth, MgSlt2 disruptants showed a defective polarized growth in the tip cells upon aging, causing substantial local enlargements culminating in large swollen cells containing two to four nuclei. The MgSlt2 disruptants showed a significantly increased sensitivity to several fungicides, including miconazole (2x), bifonazole (>4x), imazalil (5x), and cyproconazole (10x), and were hypersensitive to glucanase. Unlike the wild type, MgSlt2 disruptants did not produce aerial mycelia and did not melanize on potato dextrose agar. Although cytological analysis in planta showed normal penetration of wheat stomata by the germ tubes of the MgSlt2 disruptants, subsequently formed hyphal filaments frequently were unable to branch out and establish invasive growth resulting in highly reduced virulence, and prevented pycnidia formation. Therefore, we conclude that MgSlt2 is a new pathogenicity factor in M. graminicola.

Advances in molecular diagnosis of toxigenic Fusarium species: a review

The development of advanced molecular diagnosis for the critical toxigenic Fusarium species is considered in this review. The specific topics discussed are (1) isolation of mating type genes of Gibberella complex, (2) molecular detection of Fusarium-producing fumonisins, (3) molecular detection of Fusarium-producing trichothecenes and enniatins. Particular attention is given to the development of PCR assays for genes involved in the toxin biosynthesis that would permit the early detection of Fusarium species-producing toxins and potentially even reveal which particular toxin may be present within a food or feed product. Most of these data have been obtained within the 'De-Tox Fungi' project supported by the European Commission (QLK1-CT-1998-01380).

Mating type sequences in asexually reproducing Fusarium species

To assess the potential for mating in several Fusarium species with no known sexual stage, we developed degenerate and semidegenerate oligonucleotide primers to identify conserved mating type (MAT) sequences in these fungi. The putative alpha and high-mobility-group (HMG) box sequences from Fusarium avenaceum, F. culmorum, F. poae, and F. semitectum were compared to similar sequences that were described previously for other members of the genus. The DNA sequences of the regions flanking the amplified MAT regions were obtained by inverse PCR. These data were used to develop diagnostic primers suitable for the clear amplification of conserved mating type sequences from any member of the genus Fusarium. By using these diagnostic primers, we identified mating types of 122 strains belonging to 22 species of Fusarium. The alpha box and the HMG box from the mating type genes are transcribed in F. avenaceum, F. culmorum, F. poae, and F. semitectum. The novelty of the PCR-based mating type identification system that we developed is that this method can be used on a wide range of Fusarium species, which have proven or expected teleomorphs in different ascomycetous genera, including Calonectria, Gibberella, and Nectria.

Cloning and analysis of the mating-type idiomorphs from the barley pathogen Septoria passerinii

The genus Septoria contains more than 1000 species of plant pathogenic fungi, most of which have no known sexual stage. Species of Septoria without a known sexual stage could be recent derivatives of sexual species that have lost the ability to mate. To test this hypothesis, the mating-type region of S. passerinii, a species with no known sexual stage, was cloned, sequenced, and compared to that of its close relative S. tritici (sexual stage: Mycosphaerella graminicola). Both of the S. passerinii mating-type idiomorphs were approximately 3 kb in size and contained a single reading frame interrupted by one (MAT-2) or two (MAT-1) putative introns. The putative products of MAT-1 and MAT-2 are characterized by alpha-box and high-mobility-group sequences, respectively, similar to those in the mating-type genes of M. graminicolaand other fungi. The mating-type genes of S. passerinii and M. graminicolaare evolving rapidly, approximately ten times faster than the internal transcribed spacer region of the ribosomal DNA, and are not closely related to those from Cochliobolusor other loculoascomycetes in the order Pleosporales. Therefore, the class Loculoascomycetes may be polyphyletic. Furthermore, differences between the phylogenetic trees may indicate separate evolutionary histories for the MAT-1 and MAT-2 idiomorphs. A three-primer multiplex-PCR technique was developed that allowed rapid identification of the mating types of isolates of S. passerinii. Both mating types were present in approximately equal frequencies and often on the same leaf in fields in Minnesota and North Dakota. Analyses with isozyme and random amplified polymorphic DNA markers revealed that each isolate had a unique genotype. The common occurrence of both mating types on the same leaf and the high levels of genotypic diversity indicate that S. passerinii is almost certainly not an asexual derivative of a sexual fungus. Instead, sexual reproduction probably plays an integral role in the life cycle of S. passerinii and may be much more important than previously believed in this (and possibly other) "asexual" species of Septoria.

A combined amplified fragment length polymorphism and randomly amplified polymorphism DNA genetic kinkage map of Mycosphaerella graminicola, the septoria tritici leaf blotch pathogen of wheat

An F(1) mapping population of the septoria tritici blotch pathogen of wheat, Mycosphaerella graminicola, was generated by crossing the two Dutch field isolates IPO323 and IPO94269. AFLP and RAPD marker data sets were combined to produce a high-density genetic linkage map. The final map contained 223 AFLP and 57 RAPD markers, plus the biological traits mating type and avirulence, in 23 linkage groups spanning 1216 cM. Many AFLPs and some RAPD markers were clustered. When markers were reduced to 1 per cluster, 229 unique positions were mapped, with an average distance of 5.3 cM between markers. Because M. graminicola probably has 17 or 18 chromosomes, at least 5 of the 23 linkage groups probably will need to be combined with others once additional markers are added to the map. This was confirmed by pulsed-field gel analysis; probes derived from 2 of the smallest linkage groups hybridized to two of the largest chromosome-sized bands, revealing a discrepancy between physical and genetic distance. The utility of the map was demonstrated by identifying molecular markers tightly linked to two genes of biological interest, mating type and avirulence. Bulked segregant analysis was used to identify additional molecular markers closely linked to these traits. This is the first genetic linkage map for any species in the genus Mycosphaerella or the family Mycosphaerellaceae.

Distribution of mating type alleles in the wheat pathogen Mycosphaerella graminicola over spatial scales from lesions to continents

A total of 2035 Mycosphaerella graminicola strains collected from 16 geographic locations on four continents were assayed for the mating type locus. RFLP fingerprints were used to identify clones in each population. At the smallest spatial scale analyzed, both mating types were found among fungal strains sampled from different lesions of the same leaf as well as from different pycnidia in the same lesion. At larger spatial scales, the two mating types were found at equal frequencies across spatial scales ranging from several square meters to several thousand square kilometers. Though the absolute frequencies of the two mating types sometimes varied for different sampling units within the same spatial scale in the hierarchy (plots within a field, fields within a country, or different continents of the world), none of the differences were statistically significant from the null hypothesis of equal frequencies for the two mating types. The evolutionary forces likely to maintain the even distribution of the two mating types in this pathogen were discussed.

Isolation and characterization of the mating-type idiomorphs from the wheat septoria leaf blotch fungus Mycosphaerella graminicola

Both mating-type loci from the wheat septoria leaf blotch pathogen Mycosphaerella graminicola have been cloned and sequenced. The MAT1-2 gene was identified by screening a genomic library from the MAT1-2 isolate IPO94269 with a heterologous probe from Tapesia yallundae. The MAT1-2 idiomorph is 2772 bp and contains a single gene encoding a putative high-mobility-group protein of 394 amino acids. The opposite idiomorph was obtained from isolate IPO323, which has the complementary mating type, by long-range PCR using primers derived from sequences flanking the MAT1-2 idiomorph. The MAT1-1 locus is 2839 bp in size and contains a single open reading frame encoding a putative alpha1-domain protein of 297 amino acids. Within the nonidiomorphic sequences, homology was found with palI, encoding a membrane receptor from Aspergillus nidulans, and a gene encoding a putative component of the anaphase-promoting complex from Schizosaccharomyces pombe and a DNA-(apurinic or apyrimidinic) lyase from S. pombe. For each of the MAT genes specific primers were designed and tested on an F1 mapping population that was generated from a cross between IPO323 and IPO94269. An absolute correlation was found between the amplified allele-specific fragments and the mating type as determined by backcrosses of each F1 progeny isolate to the parental isolates. The primers were also used to screen a collection of field isolates in a multiplex PCR. An equal distribution of MAT1-1 and MAT1-2 alleles was found for most geographic origins examined.

DNA Fingerprint Probe from Mycosphaerella graminicola Identifies an Active Transposable Element

ABSTRACT DNA fingerprinting has been used extensively to characterize populations of Mycosphaerella graminicola, the Septoria tritici blotch pathogen of wheat. The highly polymorphic DNA fingerprints of Mycosphaerella graminicola were assumed to reflect the action of transposable elements. However, there was no direct evidence to support that conclusion. To test the transposable element hypothesis, the DNA fingerprint probe pSTL70 was sequenced, along with three other clones from a subgenomic library that hybridized with pSTL70. Analysis of these sequences revealed that pSTL70 contains the 3' end of a reverse transcriptase sequence plus 29- and 79-bp direct repeats. These are characteristics of transposable elements identified in other organisms. Southern analyses indicated that either the direct-repeat or reverse-transcriptase sequences by themselves essentially duplicated the original DNA fingerprint pattern, but other portions of pSTL70 contained single-copy DNA. Analysis of 60 progeny from a sexual cross between two Dutch isolates of Mycosphaerella graminicola identified several new bands that were not present in the parents. Thus, the putative transposable element probably is active during meiosis. Tests of single-spore isolates revealed gains or losses of one or more DNA fingerprint bands in 4 out of 10 asexual lines derived from isolate IPO94269. Therefore, DNA fingerprint patterns produced by the putative transposable element were capable of changes during asexual reproduction of this isolate. Probe pSTL70 did not hybridize at high stringency to genomic DNAs from other fungi related to Septoria and Mycosphaerella. These results indicate that the DNA fingerprint probe pSTL70 most likely identifies a transposable element in Mycosphaerella graminicola that may have been acquired recently, and appears to be active during both sexual and asexual reproduction.

Molecular Relationships of Fungi Within the Fusarium redolens-F. hostae Clade

ABSTRACT The evolutionary relationships of fungi in the Fusarium redolens-F. hostae clade were investigated by constructing nuclear and mitochondrial gene genealogies for 37 isolates representing the known genetic and pathogenic diversity of this lineage, together with 15 isolates from putative sister groups that include the Gibberella fujikuroi and F. oxysporum species complexes and related species. Included in the analyses were 29 isolates of F. redolens from Asparagus, Convallaria, Dianthus, Fritillaria, Hebe, Helleborus, Hordeum, Linum, Pisum, Pseudotsuga, and Zea spp., and from soil. Isolates of F. hostae analyzed included two reference isolates from Hosta spp. and six isolates from Hyacinthus spp. that originally were classified as F. oxysporum f. sp. hyacinthi. DNA sequences from a portion of the nuclear translation elongation factor 1alpha (EF-1alpha) gene and the mitochondrial small subunit (mtSSU) ribosomal RNA (rRNA) were analyzed individually and as a combined data set based on results of the nonparametric Wilcoxon signed ranks Templeton combinability test. Maximum parsimony analysis of the combined data set identified the F. redolens-F. hostae clade as a sister group to a phylogenetically diverse clade in which the G. fujikuroi species complex formed the most basal lineage. Also included in this latter clade were two unnamed Fusarium spp. that are morphologically similar to F. oxysporum and putative sister taxa comprising the F. oxysporum complex and a F. nisikadoi-F. miscanthi clade. Phylogenetic diversity in F. redolens was small; all isolates were represented by only three EF-1alpha and two mtSSU rDNA haplotypes. Both the isolates of F. redolens f. sp. asparagi and those of F. redolens f. sp. dianthi were nearly evenly distributed in the combined molecular phylogeny between the two major subclades within F. redolens.

Avirulence in the wheat septoria tritici leaf blotch fungus Mycosphaerella graminicola is controlled by a single locus

Segregation of avirulence in Mycosphaerella graminicola, a heterothallic ascomycete that causes wheat septoria tritici leaf blotch, was studied in F1, BC1, and F2 populations by inoculation assays on five wheat cultivars in the seedling stage and by amplified fragment length polymorphism and random amplified polymorphic DNA analyses. F1 was generated by crossing isolates IPO323 (avirulent) and IPO94269 (virulent). All F1, BC1, and F2 progeny isolates were virulent on the susceptible check cultivar Taichung 29 and were avirulent on the resistant check cultivar Kavkav-K4500. Avirulence segregation was observed in F1 and in several BC1 and F2 generations on the differential cultivars Shafir, Kavkaz, and Veranopolis at a 1:1 ratio. Avirulence for the three differential cultivars always cosegregated. We conclude that avirulence in isolate IPO323 is controlled by a single, seemingly complex locus.