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Susumu Takamatsu - One of the best experts on this subject based on the ideXlab platform.

  • Morphology and molecular phylogeny of a poorly known species—Erysiphe bulbouncinula (Erysiphaceae) on Koelreuteria paniculata
    Forest Pathology, 2020
    Co-Authors: Li Liu, Susumu Takamatsu, Uwe Braun, Shurong Tang, Shu-yan Liu
    Abstract:

    Erysiphe bulbouncinula (≡ Bulbouncinula bulbosa) on Koelreuteria paniculata is a powdery mildew native and endemic in China. Fresh samples of this species were collected on K. paniculata in Sichuan Province, China, in 2018. This is the fourth confirmed identification of this species. The original description in 1932 was based on one specimen from Hangzhou and then was described in Nanjing in 1990 and in Taiwan in 1993. The morphology of the new collections of this species is described and illustrated in detail, and agrees well with the original description of the type specimen except for the number of asci (8–16 asci per chasmothecia versus 7–9 asci in the type specimen). To explore the phylogenetic position of this poorly known species, three separate phylogenetic analyses, using partial 28S rDNA and the combination of internal transcribed spacer (ITS) and 28S rDNA sequences, were conducted. The results clearly showed that E. bulbouncinula form a monophyletic clade with strong bootstrap (BS) support (MP = 100%) constituting a sister clade to E. gracilis s. lat., form a subclade with Erysiphe sect. Californiomyces and then form a big group with sect. Typhulochaeta and sect. Uncinula. Phylogenetic results confirm that E. bulbouncinula is more closely allied to Erysiphe than to Phyllactinia. Thus, this species can be maintained in Erysiphe in its current circumscription, confirming Bulbouncinula as a synonym of Erysiphe.

  • Taxonomy and phylogeny of the Erysiphe lonicerae complex (Helotiales, Erysiphaceae) on Lonicera spp.
    Fungal Systematics and Evolution, 2020
    Co-Authors: M. Bradshaw, Uwe Braun, Monika Götz, Susumu Takamatsu
    Abstract:

    The phylogeny and taxonomy of powdery mildews, belonging to the genus Erysiphe, on Lonicera species throughout the world are examined and discussed. Phylogenetic analyses revealed that sequences retrieved from Erysiphe lonicerae, a widespread powdery mildew species distributed in the Northern Hemisphere on a wide range of Lonicera spp., constitutes a complex of two separate species, viz., E. lonicerae (s. str.) and Erysiphe ehrenbergii comb. nov. Erysiphe lonicerae occurs on Lonicera spp. belonging to Lonicera subgen. Lonicera (= subgen. Caprifolium and subgen. Periclymenum), as well as L. japonica. Erysiphe ehrenbergii comb. nov. occurs on Lonicera spp. of Lonicera subgen. Chamaecerasus. Phylogenetic and morphological analyses have also revealed that Microsphaera caprifoliacearum (≡ Erysiphe caprifoliacearum) should be reduced to synonymy with E. lonicerae (s. str.). Additionally, Erysiphe lonicerina sp. nov. on Lonicera japonica in Japan is described and the new name Erysiphe flexibilis, based on Microsphaera lonicerae var. flexuosa, is introduced. The phylogeny of Erysiphe ehrenbergii and E. lonicerae as well as other Erysiphe species on honeysuckle is discussed, and a survey of all species, including a key to the species concerned, is provided.

  • Revisiting a poorly known powdery mildew species: Morphology and molecular phylogeny of Erysiphe longissima
    Mycoscience, 2019
    Co-Authors: Peng-lei Qiu, Susumu Takamatsu, Shurong Tang, Guanxiu Guan, Shu-yan Liu
    Abstract:

    Abstract Erysiphe longissima is a species of Erysiphe sect. Microsphaera endemic to China. Its asexual morph is poorly known and DNA sequence data are unrecorded since its first description in 1977. In 2016 and 2017, two powdery mildew samples with asexual and sexual morphs were collected on Caragana rosea at Jilin Agricultural University, Jilin Province, China. The morphological observations suggested that the two samples belonged to E. longissima. To study the phylogenetic position of E. longissima, a phylogenetic tree was constructed based on the combined ITS and 28S rDNA sequence data. This fungus was close to E. palczewskii in phylogeny and clearly distinguished from other species of Erysiphe sect. Microsphaera. To our knowledge, this is the first detailed record of the asexual morph and molecular data of E. longissima.

  • Erysiphe azerbaijanica and e linderae two new powdery mildew species erysiphales belonging to the microsphaera lineage of Erysiphe
    Mycoscience, 2017
    Co-Authors: Lamiya V Abasova, Dilzara N Aghayeva, Susumu Takamatsu
    Abstract:

    Abstract Two new species, Erysiphe azerbaijanica on Castanea sativa and E. linderae on Lindera praecox , both belonging to the Microsphaera lineage of the genus Erysiphe are described based on morphological and molecular data. Erysiphe azerbaijanica is distinguished from other Erysiphe species occurring on Castanea spp. by its cylindrical conidia with a length/width ratio of 2–3.6, longer conidiophore, and foot-cells. Molecular analyses indicated that this species forms a clade of its own, supporting the morphological observations. Molecular phylogenetic analyses showed that E. blasti s. lat. is divided into two genetically differentiated groups associated with different host species. Based on the sequence differences in the 28S rRNA gene and ITS region, connected with differences in the number and length of appendages, the fungus on L. praecox is described as a new species, E. linderae .

  • Notes on powdery mildews (Erysiphales) in Thailand III. Erysiphe species on Fabaceae, Fagaceae, Hydrangeaceae and Lamiaceae
    Tropical Plant Pathology, 2017
    Co-Authors: Jamjan Meeboon, Susumu Takamatsu
    Abstract:

    This report provides morphological descriptions of powdery mildew specimens found on Fabaceae, Fagaceae, Hydrangeaceae and Lamiaceae and molecular phylogenetic analyses based on ITS rDNA sequences. These include 4 new host records for Erysiphe species in the world, viz., Desmodium triflorum (Fabaceae), Microtoena insuavis (Lamiaceae) and Mucuna bracteata (Fabaceae). Aeschynomene americana var. americana (Fabaceae), Sesbania grandiflora (Fabaceae) and Tamarindus indica (Fabaceae) are new host for Erysiphe trifoliorum s. lat. and Phanera purpurea (Fabaceae) is new host for Erysiphe lespedezae . In addition, 11 records of Erysiphe species new to Thailand were described.

Uwe Braun - One of the best experts on this subject based on the ideXlab platform.

  • Morphology and molecular phylogeny of a poorly known species—Erysiphe bulbouncinula (Erysiphaceae) on Koelreuteria paniculata
    Forest Pathology, 2020
    Co-Authors: Li Liu, Susumu Takamatsu, Uwe Braun, Shurong Tang, Shu-yan Liu
    Abstract:

    Erysiphe bulbouncinula (≡ Bulbouncinula bulbosa) on Koelreuteria paniculata is a powdery mildew native and endemic in China. Fresh samples of this species were collected on K. paniculata in Sichuan Province, China, in 2018. This is the fourth confirmed identification of this species. The original description in 1932 was based on one specimen from Hangzhou and then was described in Nanjing in 1990 and in Taiwan in 1993. The morphology of the new collections of this species is described and illustrated in detail, and agrees well with the original description of the type specimen except for the number of asci (8–16 asci per chasmothecia versus 7–9 asci in the type specimen). To explore the phylogenetic position of this poorly known species, three separate phylogenetic analyses, using partial 28S rDNA and the combination of internal transcribed spacer (ITS) and 28S rDNA sequences, were conducted. The results clearly showed that E. bulbouncinula form a monophyletic clade with strong bootstrap (BS) support (MP = 100%) constituting a sister clade to E. gracilis s. lat., form a subclade with Erysiphe sect. Californiomyces and then form a big group with sect. Typhulochaeta and sect. Uncinula. Phylogenetic results confirm that E. bulbouncinula is more closely allied to Erysiphe than to Phyllactinia. Thus, this species can be maintained in Erysiphe in its current circumscription, confirming Bulbouncinula as a synonym of Erysiphe.

  • Taxonomy and phylogeny of the Erysiphe lonicerae complex (Helotiales, Erysiphaceae) on Lonicera spp.
    Fungal Systematics and Evolution, 2020
    Co-Authors: M. Bradshaw, Uwe Braun, Monika Götz, Susumu Takamatsu
    Abstract:

    The phylogeny and taxonomy of powdery mildews, belonging to the genus Erysiphe, on Lonicera species throughout the world are examined and discussed. Phylogenetic analyses revealed that sequences retrieved from Erysiphe lonicerae, a widespread powdery mildew species distributed in the Northern Hemisphere on a wide range of Lonicera spp., constitutes a complex of two separate species, viz., E. lonicerae (s. str.) and Erysiphe ehrenbergii comb. nov. Erysiphe lonicerae occurs on Lonicera spp. belonging to Lonicera subgen. Lonicera (= subgen. Caprifolium and subgen. Periclymenum), as well as L. japonica. Erysiphe ehrenbergii comb. nov. occurs on Lonicera spp. of Lonicera subgen. Chamaecerasus. Phylogenetic and morphological analyses have also revealed that Microsphaera caprifoliacearum (≡ Erysiphe caprifoliacearum) should be reduced to synonymy with E. lonicerae (s. str.). Additionally, Erysiphe lonicerina sp. nov. on Lonicera japonica in Japan is described and the new name Erysiphe flexibilis, based on Microsphaera lonicerae var. flexuosa, is introduced. The phylogeny of Erysiphe ehrenbergii and E. lonicerae as well as other Erysiphe species on honeysuckle is discussed, and a survey of all species, including a key to the species concerned, is provided.

  • Erysiphe deutziicola sp. nov. (Erysiphaceae, Ascomycota), a powdery mildew species found on Deutzia parviflora (Hydrangeaceae) with unusual appendages
    MycoKeys, 2019
    Co-Authors: Peng-lei Qiu, Uwe Braun, Shu-yan Liu
    Abstract:

    A powdery mildew (Erysiphales) has recently been collected on leaves of an ornamental shrub Deutziaparviflora in Baihua Mountain, Beijing, China. Microscopic examination of the chasmothecia suggested a species belonging to Erysiphesect.Erysiphe, above all due to mycelioid chasmothecial appendages, although circinate apices of the appendages were rather in favour of Erysiphesect.Uncinula, which is a fairly rare combination of appendage characteristics in Erysiphe. Phylogenetic analyses of ITS and 28S rDNA sequences demonstrated that the two examined powdery mildew collections on D.parviflora clustered together as an independent lineage within Erysiphe with 100% bootstrap support, representing a species of its own, which is phylogenetically allied to, but clearly distinct from Erysiphedeutziae and, in addition, morphologically quite different from all known Erysiphe species on hosts belonging to the Hydrangeaceae. The new species on D.parviflora is described as Erysiphedeutziicola.

  • From leaf to continent: The multi-scale distribution of an invasive cryptic pathogen complex on oak
    Fungal Ecology, 2018
    Co-Authors: Marie-laure Desprez-loustau, Uwe Braun, Marie Massot, Maude Toigo, Tania Fort, Ayse Gülden Aday Kaya, Johanna Boberg, Xavier Capdevielle, Thomas Cech, Anne Chandelier
    Abstract:

    The spatial distribution and niche differentiation of three closely related species (Erysiphe alphitoides, Erysiphe quercicola and Erysiphe hypophylla) causing oak powdery mildew was studied at scales ranging from the European continent, where they are invasive, to a single leaf. While E. alphitoides was dominant at all scales, E. quercicola and E. hypophylla had restricted geographic, stand and leaf distributions. The large-scale distributions were likely explained by climatic factors and species environmental tolerances, with E. quercicola being more frequent in warmer climates and E. hypophylla in colder climates. The extensive sampling and molecular analyses revealed the cryptic invasion of E. quercicola in nine countries from which it had not previously been recorded. The presence of the three species was also strongly affected by host factors, such as oak species and developmental stage. Segregation patterns between Erysiphe species were observed at the leaf scale, between and within leaf surfaces, suggesting competitive effects.

  • First report of Erysiphe baptisiae on Baptisia in UK with emended description
    2014
    Co-Authors: Roger T.a. Cook, Alick Henrici, Uwe Braun
    Abstract:

    Abstract: Cook, R. T. A., Henrici, A. & Braun, U. 2014: First report of Erysiphe baptisiae on Baptisia in UK with emended description. Schlechtendalia 28 : 41–48. Erysiphe baptisiae has been found for the first time in UK. Taxonomy and morphology of this species are discussed, and an emended description and illustrations are provided. Zusammenfassung: Cook, R. T. A., Henrici, A. & Braun, U. 2014: Erstangabe von Erysiphe baptisiae auf Baptisia in Grosbritannien mit emendierter Beschreibung. Schlechtendalia 28 : 41–48. Erysiphe baptisiae wurde erstmalig in Grosbritannien gefunden. Taxonomie und Morphologie dieser Art werden diskutiert, erganzt durch eine emendierte Beschreibung und Abbildungen.

Jamjan Meeboon - One of the best experts on this subject based on the ideXlab platform.

Saranya Limkaisang - One of the best experts on this subject based on the ideXlab platform.

  • phylogeny and taxonomy of the oak powdery mildew Erysiphe alphitoides sensu lato
    Fungal Biology, 2007
    Co-Authors: Susumu Takamatsu, Saranya Limkaisang, Sawanee Komun, Uwe Braun, Yukio Sato, James H Cunnington
    Abstract:

    Phylogenetic analyses of Erysiphe alphitoides s. lat. using sequences of the rDNA ITS region and the D1/D2 domains of the 28S rDNA revealed a complex consisting of several genetically and morphologically distinguished taxa, including the already described Erysiphe alphitoides s. str. and E. hypophylla. The ascomata (chasmothecia) of E. hypophylla are morphologically very similar to those of E. alphitoides, but the two species are easily distinguishable by their symptoms, as well as the shape and size of the conidia. The fungus on Quercus phillyraeoides, distributed in warmer regions in southern Japan, is genetically clearly separated from E. alphitoides s. str., and morphologically characterized by having chasmothecia with appendages consistently shorter than the chasmothecial diameter. This fungus, named Erysiphe quercicola in this paper, is also able to infect some other oak species, and it is genetically identical with anamorphs on some tropical trees of other host genera. Collections of E. alphitoides s. lat. on Quercus acutissima and Q. variabilis, both belonging to Quercus sect. Cerris, are genetically distinct from E. alphitoides s. str., E. hypophylla and E. quercicola. They form two genetically and morphologically differentiated groups. The hypophyllous taxon on Q. acutissima and Q. variabilis, named Erysiphe hypogena in this paper, is characterized by forming distinctive persistent hypophyllous mycelial patches, causing necrotic discolouration of the host tissue. The epiphyllous taxon on these hosts, for which the name E. epigena is proposed, differs in having epiphyllous mycelium, smaller chasmothecia with fewer appendages, and does not cause leaf discolouration.

  • Phylogeny and taxonomy of powdery mildew fungi of Erysiphe sect. Uncinula on Carpinus species
    Mycological Progress, 2006
    Co-Authors: Uwe Braun, Saranya Limkaisang, Susumu Takamatsu, Vasyl P. Heluta, Rangsi Divarangkoon, Roger Cook, Herbert Boyle
    Abstract:

    A phylogenetic analysis of the Erysiphe with uncinuloid ascoma appendages ( Erysiphe section Uncinula , Erysiphales, Ascomycota ) on Carpinus spp. was done using sequences of the rDNA ITS regions and the D1/D2 domains of the 28S rDNA. These results, combined with morphological data, revealed a complex consisting of several distinct taxa. These included the already described Erysiphe carpinicola on C. japonica distinguishable from the Erysiphe sp. on C. betulus and C. tschonoskii as well as the one on C . laxiflora . Thus, it was shown that Oidium carpini , described from Europe on Carpinus betulus , the powdery mildew with uncinula-like ascomata, recently found in Europe on this host, as well as an Erysiphe on C. tschonoskii in Japan, described previously as E. carpinicola , all belong to a single new species, named E. arcuata in this paper. As the powdery mildew on C. laxiflora was also distinct from other known species, it is named E. carpini-laxiflorae in this paper. The already described E. pseudocarpinicola and Erysiphe sp. on Carpinus cordata are two additional taxa, which are morphologically and genetically distinguished from the other species of Erysiphe sect. Uncinula on Carpinus spp.

  • molecular phylogenetic and morphological analyses of oidium heveae a powdery mildew of rubber tree
    Mycoscience, 2005
    Co-Authors: Saranya Limkaisang, Sawanee Komun, Kon Wui Liew, Edson Luiz Furtado, Baharuddin Salleh, Yukio Sato, Susumu Takamatsu
    Abstract:

    Powdery mildew of rubber tree caused by Oidium heveae is an important disease of rubber plantations worldwide. Identification and classification of this fungus is still uncertain because there is no authoritative report of its morphology and no record of its teleomorphic stage. In this study, we compared five specimens of the rubber powdery mildew fungus collected in Malaysia, Thailand, and Brazil based on morphological and molecular characteristics. Morphological results showed that the fungus on rubber tree belongs to Oidium subgen. Pseudoidium. Nucleotide sequence analysis of the ribosomal DNA internal transcribed spacer (ITS) region and the large subunit rRNA gene (28S rDNA) were conducted to determine the relationships of the rubber powdery mildew fungus and to link this anamorphic fungus with its allied teleomorph. The results showed that the rDNA sequences of the two specimens from Malaysia were identical to a specimen from Thailand, whereas they differed by three bases from the two Brazilian isolates: one nucleotide position in the ITS2 and two positions in the 28S sequences. The ITS sequences of the two Brazilian isolates were identical to sequences of Erysiphe sp. on Quercus phillyraeoides collected in Japan, although the 28S sequences differed at one base from sequences of this fungus. Phylogenetic trees of both rDNA regions constructed by the distance and parsimony methods showed that the rubber powdery mildew fungus grouped with Erysiphe sp. on Q. phillyraeoides with 100% bootstrap support. Comparisons of the anamorph of two isolates of Erysiphe sp. from Q. phillyraeoides with the rubber mildew did not reveal any obvious differences between the two powdery mildew taxa, which suggests that O. heveae may be an anamorph of Erysiphe sp. on Q. phillyraeoides. Cross-inoculation tests are required to substantiate this conclusion.

  • molecular phylogenetic and morphological analyses of oidium heveae a powdery mildew of rubber tree
    Mycoscience, 2005
    Co-Authors: Saranya Limkaisang, Sawanee Komun, Kon Wui Liew, Edson Luiz Furtado, Baharuddin Salleh, Yukio Sato, Susumu Takamatsu
    Abstract:

    Powdery mildew of rubber tree caused by Oidium heveae is an important disease of rubber plantations worldwide. Identification and classification of this fungus is still uncertain because there is no authoritative report of its morphology and no record of its teleomorphic stage. In this study, we compared five specimens of the rubber powdery mildew fungus collected in Malaysia, Thailand, and Brazil based on morphological and molecular characteristics. Morphological results showed that the fungus on rubber tree belongs to Oidium subgen. Pseudoidium. Nucleotide sequence analysis of the ribosomal DNA internal transcribed spacer (ITS) region and the large subunit rRNA gene (28S rDNA) were conducted to determine the relationships of the rubber powdery mildew fungus and to link this anamorphic fungus with its allied teleomorph. The results showed that the rDNA sequences of the two specimens from Malaysia were identical to a specimen from Thailand, whereas they differed by three bases from the two Brazilian isolates: one nucleotide position in the ITS2 and two positions in the 28S sequences. The ITS sequences of the two Brazilian isolates were identical to sequences of Erysiphe sp. on Quercus phillyraeoides collected in Japan, although the 28S sequences differed at one base from sequences of this fungus. Phylogenetic trees of both rDNA regions constructed by the distance and parsimony methods showed that the rubber powdery mildew fungus grouped with Erysiphe sp. on Q. phillyraeoides with 100% bootstrap support. Comparisons of the anamorph of two isolates of Erysiphe sp. from Q. phillyraeoides with the rubber mildew did not reveal any obvious differences between the two powdery mildew taxa, which suggests that O. heveae may be an anamorph of Erysiphe sp. on Q. phillyraeoides. Cross-inoculation tests are required to substantiate this conclusion.

  • two Erysiphe species associated with recent outbreak of soybean powdery mildew results of molecular phylogenetic analysis based on nuclear rdna sequences
    Mycoscience, 2002
    Co-Authors: Susumu Takamatsu, Saranya Limkaisang, Hyeon-dong Shin, U Paksiri, Y Taguchi, Thi N Binh, Yukio Sato
    Abstract:

    Serious outbreaks of powdery mildew by a fungus belonging to the mitosporic genus Oidium subgenus Pseudoidium have been reported on soybean (Glycine max) in a wide area of eastern Asia since 1998. The taxonomic and phylogenetic placement of the causal fungus has not yet been determined because of lack of the perfect stage. We found ascomata having mycelioid appendages on a single leaf of soybean infested by powdery mildew. Molecular phylogenetic analysis was conducted based on a total of 14 sequences of the rDNA internal transcribed spacer (ITS) region from 13 soybean and wild soybean (Glycine soja) materials collected in Japan, Korea, Vietnam, and the United States, combined with 47 sequence data obtained from the DNA databases. It was revealed that two Erysiphe species were associated with the outbreak of soybean powdery mildew. There was 16% difference between the two species in genetic divergence of the ITS sequence. One species with perfect stage has an ITS sequence identical to that of Erysiphe glycines on Amphicarpaea and is identified as Erysiphe glycines based on the ITS sequence and morphology of ascomata. The second species, without the perfect stage, is likely to be Erysiphe diffusa (= Microsphaera diffusa), known as the fungus causing soybean powdery mildew in the United States, because the ITS sequences are identical to those from materials collected in the United States. However, we need materials having ascomata of E. diffusa to confirm the species name.

Aleš Lebeda - One of the best experts on this subject based on the ideXlab platform.

  • Erysiphe catalpae and Erysiphe elevata in Europe
    Mycological Progress, 2004
    Co-Authors: Nosratollah Ale-agha, Aleš Lebeda, Uwe Braun, Adrien Bolay, Benno Feige, Horst Jage, Volker Kummer, Marcin Piątek, Hyeon-dong Shin, Katarína Zimmermannová-pastirčaková
    Abstract:

    The recent epidemic spread of the North American powdery mildew Erysiphe elevata in Europe is described and discussed. Since 2002, this plant pathogenic fungus has been collected on Catalpa bignonioides, C. erubescens and C. speciosa in the Czech Republic, Germany, Hungary, Slovakia and Switzerland. The diagnostically important anamorph of E. elevata , so far unknown, is described and illustrated in detail. Type material of Erysiphe catalpae and two specimens of E. catalpae recently collected in Poland have been examined and compared with E. elevata . The anamorph as well as the teleomorph of E. catalpae proved to be easily distinguishable from E. elevata . The supposition that E. catalpae , introduced in Armenia, was based on immature ascomata of E. elevata proved to be wrong. The origin and distribution of E. catalpae are discussed, and a key to powdery mildew fungi on Catalpa spp. in Europe is provided.

  • comparative morphological studies on tomato powdery mildew oidium neolycopersici
    Acta Phytopathologica Et Entomologica Hungarica, 2002
    Co-Authors: B Mieslerova, Aleš Lebeda, Roy Kennedy, R. Novotny
    Abstract:

    Fourteen isolates of tomato powdery mildew (Oidium neolycopersici) and one isolate of the following species: Podosphaera fusca (= Sphaerotheca fusca), Erysiphe orontii (cucumber powdery mildews), Erysiphe cicho­ra­cearum (lettuce powdery mildew) and Erysiphe aquilegiae var. ranunculi (Ranunculus lingua powdery mildew) were used for com­parative morpho­logical studies. Basic characteristics of the anamorphs, including outer conidial wall patterns, were compared using light and scanning electron microscopy (SEM). In main morphological features, O. neo­lyco­persici was strongly differentiated from E. cichoracearum, E. orontii and P. fusca. However, based on morphological features (e.g. germination type; appres­sorium shape; morphology of conidiophores) O. neolyco­per­sici was close to E. aquilegiae var. ranunculi (both belong to Oidium subgen. Pseudo­idium) and it probably could be placed to Erysiphe sect. Erysiphe (= Erysiphe s. str.)

  • Case study of host-pathogen interaction: tomato (Lycopersicon spp.)–tomato powdery mildew (Oidium lycopersici) – a review
    Plant Protection Science, 2000
    Co-Authors: Aleš Lebeda, B Mieslerova
    Abstract:

      The present paper tries to demonstrate progress and gap of knowledge in plant pathology through the tomato - tomato powdery mildew host-pathogen interaction as a model. Tomato powdery mildew (Oidium lycopersici) has caused serious damages on glasshouse tomato (Lycopersicon esculentum) crops during the last approximately 15 years. Although the absence of tcleomorph stage did not allow exact taxonomic classification of the pathogen, comparative morphological studies using light and scanning electron microscopy revealed that Oidium lycopersici might be included to the Erysiphe sect. Erysiphe (close to Erysiphe aqui­ legiae var. ranunculi). Effective resistance sources to 0. lycopersici were found mainly in wi ld Lycopersicon hirsutum and L. penne/lii (confirmed by testing with four different 0. lycopersici isolates). Available information on the pathogenic variability of 0. lycopersici is given; host range experiments revealed considerable differences in abi lity of different 0. lycopersici isolates to infect cucumber and tobacco. postulating existence of different pathotypcs lformae specialist of pathogen. Similarly, some Lycopersicon spp. genotypes showed remarkable differential reactions with pathogen isolates, indicating existence of different pathogen races. Information regarding recently detected mechanisms and basis of resistance in Lycopersicon spp. are also men­ tioned. However, more research based on classical, biochemical and molecular approaches is also needed.