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SESSION 1 - Discovery - New horizons in plant pathology - page 45 / 65





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2 Martin-Luther-Universität, FB. Biologie, Institut für Geobotanik und Botanischer   Garten, Neuwerk 21, D-06099 Halle (Saale), Germany.

Mycosphaerella is one of the largest genera of ascomycetes, containing more than 23 accepted anamorph genera.  One of these genera, Cercospora, contains species which are important plant pathogens on numerous hosts.  Traditionally, species in Cercospora were named after the host from which they were isolated.  This led to a situation where approximately 3000 species names have been proposed.  Recently, the genus was revised and 659 species were recognized, with 281 names being treated as synonyms of C. apii s.lat.  This approach has made the C. apii complex a dumping ground for all species that are morphologically similar to C. apii.  It is known that these species, which lack a Mycosphaerella teleomorph, cannot be distinguished based on their ITS DNA sequences.  In this study, 173 Cercospora isolates, most of which are synonyms of C. apii, were sequenced for four genomic loci, namely ITS (ITS1, 5.8S rDNA and ITS2), partial elongation-factor 1-alpha, calmodulin and actin genes.  These sequence data were combined, and a phylogenetic tree using neighbor joining analysis with the Kimura 2-parameter substitution model in PAUP* 4b10 obtained.  The isolates used in the study encompass 49 species from 73 different host plants and 24 different countries.  The aim of this study was to test the following hypotheses: 1)  there are only a few true Cercospora species that have wide host ranges; 2)  Cercospora species should be named after their hosts; and 3)  The C. apii complex consists of different formae specialis specific to different hosts.  The phylogenetic tree is used to evaluate these hypotheses, and to provide support for their acceptability or rejection.


Species of Phaeoacremonium associated with human infections and environmental reservoirs in infected woody plants

Lizel Mostert, Johannes Z. (Ewald) Groenewald, Richard C. Summerbell, Vincent Robert and Pedro W. Crous Centraalbureau voor Schimmelcultures, Utrecht, The Netherlands

To date, three species of Phaeoacremonium have been associated with phaeohyphomycosis.  They are Pm. parasiticum (formerly Phialophora parasitica), Pm. inflatipes and Pm. rubrigenum.  Numerous unknown isolates resembling Phaeoacremonium spp. have in recent years been isolated from human patients, as well as from woody plants that appear to be the main environmental source of these fungi.  Nine new Phaeoacremonium species, of which six were obtained as etiologic agents of human opportunistic infection, are reported here.  The main economically important plant species involved are the cultivated grape, Vitis vinifera, as well as the date palm Phoenix dactylifera and the kiwi fruit vine, Actinidia chinensis.  Of these Petri Disease on grapevines has been the most extensively studied.  This disease is caused by a complex of vascular pathogens, namely Phaeomoniella chlamydospora and several species of Phaeoacremonium.  Diseased grapevines are characterized by stunted growth and die-back symptoms.  The different Phaeoacremonium species can be identified based on their cultural and morphological characters, and the identifications are strongly supported in phylogenetic analyses of partial sequences of the actin and -tubulin genes.  A conventional key based on cultural and morphological characters, as well as a multiple-entry electronic key based on morphological, cultural and -tubulin sequence data, were developed to facilitate routine species identification.  All available Pm. inflatipes isolates previously reported from human infections could be shown not to represent this species, but instead to belong to new taxa.


ITS phylogeny reveals cryptic species within the Mycosphaerella leaf spot complex occurring on banana

Mahdi Arzanlou, Olaf Daviena, Edwin C.A. Abeln, Johannes Z. (Ewald) Groenewald and Pedro W. Crous

Centraalbureau voor Schimmelcultures, Uppsalalaan 8, 3584 CT Utrecht, The Netherlands

Mycosphaerella leaf spot is regarded as a serious foliar disease of banana, and is responsible for major economic losses to banana growers worldwide.  Although several species of Mycosphaerella have been reported from this host, four species appear to be rather common, and are regarded as the most damaging, namely M. musicola (causal agent of Sigatoka disease), M. fijiensis (causal agent of black leaf streak disease), M. musae (causal agent of Mycosphaerella speckle) and M. eumusae (causal agent of eumusae leaf spot). In the past, the taxonomy of these species has been based on minute morphological differences present in their anamorphs, and the phylogenetic relationship among these species is poorly understood.  In this study we present a phylogeny of a global set of Mycosphaerella isolates from banana, based on Internal Transcribed Spacer (ITS) DNA sequences.  The phylogenetic tree obtained from these data revealed 13 distinct clades.  Some of the clades showed little variation, and correlated with sequence data of other known species of Mycosphaerella.  Significant variation was observed within M. eumusae, M. musae and M. musicola, while little variation was found to be present in M. fijiensis.  Contrary to earlier belief, this study has revealed that several species of Mycosphaerella are associated with leaf spot disease symptoms on this host, and that some of these appear to be new.  Further work is currently in progress to determine if the genetic variation observed in this study is supported by other gene loci and morphological characters.



Leišová L., Kučera L., Kučerová D., Sýkorová S., Chrpová J., Šíp V.

RICP, Drnovská 507, 161 00 Prague 6 – Ruzyně, Czech Republic, e-mail: leisova@vurv.cz

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