8,958 research outputs found

    Taxonomy and phylogeny of the genus Mycosphaerella and its anamorphs

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    Historically plant pathogenic species of Mycosphaerella have been regarded as host-specific, though this hypothesys has proven difficult to test largely due to the inavailability of fungal cultures. During the course of the past 20 years a concerted effort has been made to collect these fungi, and devise methods to cultivate them. Based on subsequent DNA sequence analyses the majority of these species were revealed to be host-specific, though some were not, suggesting that no general rule can be applied. Furthermore, analysis of recent molecular data revealed Mycosphaerella to be poly- and paraphyletic. Teleomorph morphology was shown to be too narrowly defined in some cases, and again too widely in others. Mycosphaerella and Teratosphaeria as presently circumscribed represent numerous different genera, many of which can be recognised based on the morphology of their 30 odd associated anamorph genera. Although Mycosphaerella is generally accepted to represent one of the largest genera of ascomycetous fungi, these data suggest that this is incorrect, and that Mycosphaerella should be restricted to taxa linked to Ramularia anamorphs. Furthermore, other anamorph form genera with Mycosphaerella-like teleomorphs appear to represent genera in their own right

    Mycosphaerella podagrariae - a necrotrophic phytopathogen forming a special cellular interaction with its host Aegopodium podagraria

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    We present a new kind of cellular interaction found between Mycosphaerella podagrariae and Aegopodium podagraria, which is remarkably different to the interaction type of the obligate biotrophic fungus Cymadothea trifolii, another member of the Mycosphaerellaceae (Capnodiales, Dothideomycetes, Ascomycota) which we have described earlier. Observations are based on both conventional and cryofixed material and show that some features of this particular interaction are better discernable after chemical fixation. We were also able to generate sequences for nuclear ribosomal DNA (complete SSU, 5.8 S and flanking ITS-regions, D1–D3 region of the LSU) confirming the position of M. podagrariae within Mycosphaerellacea

    Sequencing the Major Mycosphaerella Pathogens of Wheat and Banana

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    Mycosphaerella is one of the largest genera of plant-pathogenic fungi with more than 1,000 named species, many of which are important pathogens causing leaf spotting diseases in a wide variety of crops including cereals, citrus, banana, eucalypts, soft fruits and horticultural crops. A few species of Mycosphaerella cause disease in humans and other vertebrates. An international project was initiated to sequence the genomes of M. graminicola and M. fijiensis, two of the most economically important pathogens of wheat and banana, respectively, along with 40,000 ESTs from M. fijiensis and the related maize pathogen Cercospora zeae-maydis. The 9x M. graminicola genome size is 39.8 Mb with chromosome sizes from 548 kb to 6 Mb and a complete circular mitochondrial genome of 43,947 bp. Our data indicate that M. graminicola has both the largest chromosome number and the smallest chromosome sizes recorded among filamentous ascomycetes. The Mycosphaerella Genomics Consortium, which was established in 2003, decided to use M. graminicola as the model to develop more genetic and genomic research on M. fijiensis. Since 2003, M. fijiensis EST sequencing has resulted in more than 30,000 ESTs, and the genome sequencing was recently finished at 7.8x. The genome size of M. fijiensis is 80% larger than that of M. graminicola. The completed mitochondrial sequence is more then twice as large, and the estimated nuclear genome size is approximately 72 Mb. The extension of the genome size of M. fijiensis seems to be mostly due to additional repeated sequences. The status of Mycosphaerella sequencing will have a significant effect on future studies aimed at the control of black leaf streak disease. The current status of both sequencing projects and other initiatives to exploit this information and to put it into a multidisciplinary approach focusing on sustainable management of the disease will be discusse

    Molecular Diagnostics in the Mycosphaerella Leaf Spot Disease Complex of Banana and for Radopholus similis

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    Mycosphaerella leaf spots and nematodes threaten banana cultivation worldwide. The Mycosphaerella disease complex 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, since their symptoms and life cycles are rather similar. Diagnosing these diseases and the respective causal agents is based on the presence of host symptoms and fungal fruiting structures, but is time consuming and not conducive to preventive management. In the present study, we developed rapid and robust species-specific diagnostic tools to detect and quantify M. fijiensis, M. musicola and M. eumusae. Conventional species-specific PCR primers were developed based on the actin gene that detected as little as 100, 1 and 10 pg/µl DNA from, respectively, M. fijiensis, M. musicola and M. eumusae. Furthermore, TaqMan real-time quantitative PCR assays that were developed based on the ß-tubulin gene detected quantities as low as 1 pg/µl DNA of each species from pure cultures and 1.6 pg/µl DNA/mg of M. fijiensis from dry leaf tissue. The efficacy of the tests was validated using naturally infected banana leaves. Similar technology has been used to develop a quantitative PCR assay for the banana burrowing nematode, Radopholus similis, which is currently being validate

    Flower blight of chrysanthemums : the causal fungi and their control : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University

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    The commercial chrysanthemum commonly grown in New Zealand is botanically identified as Chrysanthemum morifoliurr. Ramat. and is believed to have originated in China. As the family name Compositae suggests the individual flower ('flower head') is a composite arrangement of two types of florets, namely ray florets with well developed petals, and disc florets with tubular or poorly developed petals. Production of commercial chrysanthemums basically comprises three categories: (i) cut flowers; (ii) cuttings; (iii) container or pot plants. Chrysanthemums are probably grown by more floriculturalists than any other flower crop. Much of its popularity is attributed to the wide range of colours and forms and the fact that it can be grown either as a pot plant or for cut flowers. Another important characteristic of the chrysanthemum is the long keeping quality of the flowers, a feature which is much appreciated by retailers and consumers. In the United States of America the chrysanthemum or 'mum' is the most popular flower, surpassing both the rose and carnation in total wholesale value. [FROM INTRODUCTION

    Pseudocercospora opuntiae sp. nov., the causal organism of cactus leaf spot in Mexico.

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    Pseudocercospora opuntiae is newly described from Opuntia spp. from Mexico, where it causes a serious disease of this host. Although P. opuntiae is morphologically similar to other members of the genus with pigmented conidia and conidiophores, and unthickened, not darkened conidiogenous scars, DNA sequence data of the ITS region revealed that it clusters distant from other species of Pseudocercospora within Mycosphaerella. These data support the assumption that Pseudocereospora is paraphyletic within Mycosphaerella

    Sensitivity towards DMI fungicides and haplotypic diversity of their CYP51 target in the Mycosphaerella graminicola population of Flanders

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    Septoria leaf blotch, caused by the fungus Mycosphaerella graminicola, is the most important wheat disease in Northwestern Europe, and is currently controlled by fungicide applications. Since the spread of resistance to methyl benzimidazole carbamates (MBCs) and quinone outside inhibitors (QoIs) in European countries, reliable control is mainly dependent upon sterol 14 alpha-demethylation inhibitors (DMIs). In the last decades however, a slow shift towards reduced sensitivity of M. graminicola to DMIs has been observed. This shift is caused mainly by mutations in the CYP51 gene encoding the 14 alpha-demethylase target protein for these fungicides. In this work, M. graminicola isolates were sampled at fields spread over Flanders, Belgium. In vitro assays were used to analyze the sensitivity of the Flemish M. graminicola population towards different DMIs. Sequencing of the CYP51 gene of these isolates allowed us to identify and map the haplotypes in this population. The results showed that there is a large variability in DMI sensitivity between the isolates, even within one field, which is reflected in a high diversity in CYP51 haplotypes within the M. graminicola population in Flanders. Next to some haplotypes that were not described in literature before, we found that the population is dominated by CYP51 haplotypes which were previously associated with increased resistance towards DMIs

    Niche sharing reflects a poorly understood biodiversity phenomenon

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    Eucalyptus spp. are susceptible to a large number of foliar pathogens, some of which can cause serious defoliation and die-back. In this study, a single leaf spot on a Eucalyptus leaf collected in Madagascar revealed an unusual association of microfungi with disease symptoms. Initial observations indicated that the leaf spot was associated with Mycosphaerella marksii, a common pathogen of eucalypts. However, more intensive scrutiny showed the presence of several other microfungi co-occurring in this, and other leaf spots on the leaf. A total of 41 single conidial propagules were subsequently obtained from a single lesion for morphological study and DNA sequence comparisons. Based on these data, 11 members of the Capnodiales, including one species of Pestalotiopsis (Xylariales), were observed. Of the capnodialean taxa, nine could be cultivated, which revealed one known species, M. marksii, two taxa in the Cladosporium cladosporioides species complex that were not treated here, and six new species, including Passalora intermedia, Pseudocercospora madagascariensis, Teratosphaeria hortaea, Toxicocladosporium chlamydosporum, T. rubrigenum and T. veloxum. Results of this study highlight a remarkable fungal biodiversity that can occur within a very specific niche. Furthermore, the results emphasise the importance of verifying the identity of fungal isolates in culture, as many taxa, especially those of the Capnodiales, frequently co-occur in the same niche, lesion or leaf spo

    Variable number of tandem repeat markers in the genome sequence of Mycosphaerella fijiensis, the causal agent of black leaf streak disease of banana (Musa spp)

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    ABSTRACT. We searched the genome of Mycosphaerella fijiensis for molecular markers that would allow population genetics analysis of this plant pathogen. M. fijiensis, the causal agent of banana leaf streak disease, also known as black Sigatoka, is the most devastating pathogen attacking bananas (Musa spp). Recently, the entire genome sequence of M. fijiensis became available. We screened this database for VNTR markers. Forty-two primer pairs were selected for validation, based on repeat type and length and the number of repeat units. Five VNTR markers showing multiple alleles were validated with a reference set of isolates from different parts of the world and a population from a banana plantation in Costa Rica. Polymorphism information content values varied from 0.6414 to 0.7544 for the reference set and from 0.0400 and 0.7373 for the population set. Eighty percent of the polymorphism information content values were above 0.60, indicating that the markers are highly informative. These markers allowed robust scoring of agarose gels and proved to be useful for variability and population genetics studies. In conclusion, the strategy we developed to identify and validate VNTR markers is an efficient means to incorporate markers that can be used for fungicide resistance management and to develop breeding strategies to control banana black leaf streak disease. This is the first report of VNTR-minisatellites from the M. fijiensis genome sequence. Key words: Molecular markers; VNTRs; Genetic diversity; Population genetics; Black Sigatok
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