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Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, 0002, South Africa
H. Myburg
B.D. Wingfield
Department of Genetics, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, 0002, South Africa
M.J. Wingfield
Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, 0002, South Africa
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ABSTRACT |
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Recent phylogenetic studies on the members of the Diaporthales have shown that the order includes a number of distinct phylogenetic groups. These groups represent the Gnomoniaceae, Melanconidaceae, Valsaceae, Diaporthaceae and Togniniaceae. New groups representing undescribed families also have emerged and they have been referred to as the Schizoparme, Cryphonectria-Endothia and Harknessia complexes. In this study we define the new family Cryphonectriaceae (Diaporthales) to accommodate genera in the Cryphonectria-Endothia complex. These genera can be distinguished from those in other families or undescribed groups of the Diaporthales by the formation of orange stromatic tissue at some stage of their life cycle and a purple reaction in KOH and a yellow reaction in lactic acid associated with pigments in the stromatic tissue or in culture.
Key words: Amphilogia, Cryptodiaporthe corni, LSU sequences, Rostraureum
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSTAXONOMYDISCUSSIONLITERATURE CITED |
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). Genera in this order occur on a wide diversity of plant substrates as either saprophytes or parasites (Barr 1978). The parasites include some of the most economically and ecologically important pathogens of trees and agricultural crops. Examples of such a pathogen are Cryphonectria parasitica (Murrill) M. E. Barr, which has devastated American chestnut (Castanea dentata Borkh.) populations in North America (Anagnostakis 1987, Heiniger and Rigling 1994), and Diaporthe phaseolorum (Cooke & Ellis) Sacc., the causal agent of stem canker of soybeans (Kulik 1984).
Members of the Diaporthales are united morphologically by a Diaporthe-type centrum (Alexopoulos and Mims 1978, Barr 1978). Morphological characteristics include perithecia with long necks that are located in pseudostromata with no paraphyses and thick-walled asci that are either evanescent with short stalks or intact (Alexopoulos and Mims 1978, Hawks-worth et al 1995). Features such as the presence or absence of stromatic tissue, stromatal tissue type, the position of the perithecia and perithecial beaks relative to the substrate, ascospore shape and ascospore septation have been used to differentiate families and genera in the Diaporthales (Barr 1978).
Six families currently are recognized in the Diaporthales (Eriksson 2005b). These include the Diaporthaceae Höhn. ex Wehm., Gnomoniaceae G. Winter, Melanconidaceae G. Winter, Valsaceae Tul. & C. Tul., Vialaeaceae P.F. Cannon and Togniniaceae Réblová, L. Mostert, W. Gams & Crous. This classification has largely emerged from recent DNA sequence comparisons of Castlebury et al (2002), who compared genera representing the families previously recognized in the Diaporthales. The Togniniaceae is a new family that was described by Réblová et al (2004). The family level status of the Vialaeaceae, established by Cannon (Cannon 1995), has not been confirmed with DNA sequence data (Castlebury et al 2002).
In addition to the described families groups not recognized previously also were noted by Castlebury et al (2002). One of these groups includes species of Schizoparme Shear and their Coniella Höhn. and Pilidiella Petr. & Syd. anamorphs, which have been referred to as members of the Schizoparme complex (Castlebury et al 2002). The second group included species of Cryphonectria (Sacc.) Sacc. and Endothia Fr.; this was referred to as the Cryphonectria-Endothia complex (Castlebury et al 2002). Species of Harknessia M.C. Cooke and allied genera Dwiroopa C.V. Subramanian & J. Muthumary and Apoharknessia Crous & S. Lee also formed a group within the Diaporthales, although not well supported phylogenetically with the available DNA sequence data (Castlebury et al 2002, Lee et al 2004). This group could not be described as a family because the status of Wuestneia Auersw. ex Fuckel as the teleomorph of this coelomycete genus still must be confirmed (Lee et al 2004). In addition to these undescribed complexes of species, several species, such as Greeneria uvicola (Berk. & M.A. Curtis) Punith., did not group in any of the families or undescribed complexes (Castlebury et al 2002). This suggests that additional groups might emerge in the Diaporthales as more species are described or included in phylogenetic comparisons.
Various taxonomic studies considering genus and species delimitation for species of Cryphonectria and Endothia have been conducted recently (Venter et al 2002; Gryzenhout et al 2004, 2005a, Gryzenhout et al b; Myburg et al 2004a). These studies have included the recognition of at least four new genera containing species previously placed in Cryphonectria. Of these Chrysoporthe Gryzenh. & M. J. Wingf. was described to accommodate the important stem canker pathogen Cryphonectria cubensis (Bruner) Hodges and two additional species, Chrysoporthe austroafricana Gryzenh. & M.J. Wingf. and the anamorph species Chrysoporthella hodgesiana Gryzenh. & M.J. Wingf. (Gryzenhout et al 2004). Rostraureum Gryzenh. & M.J. Wingf. was described to include the fungus previously known as Cryphonectria longirostris (Earle) Micales & Stipes and also includes Rostraureum tropicale Gryzenh. & M.J. Wingf., a pathogen of Terminalia ivorensis A. Chev. trees in Ecuador (Gryzenhout et al 2005a). Another genus, represented by isolates from Elaeocarpus spp. in New Zealand and including Cryphonectria gyrosa (Berk. & Broome) Sacc., was identified in a study by Myburg et al (2004a) and subsequently was described as Amphilogia Gryzenh. & M.J. Wingf. (Gryzenhout et al 2005b). A genus closely related to Cryphonectria and Endothia and representing isolates from Syzygium aromaticum (L.) Murr. & Perry (clove) in Indonesia, was recognized in a study by Myburg et al (2003). This genus was not assigned a name because insufficient herbarium material, linked to isolates, is available.
A collection of isolates representing species of Cryphonectria and Endothia, as well as those of the newly described genera, has provided the opportunity to substantially expand the LSU DNA sequence dataset for the Cryphonectria-Endothia complex defined by Castlebury et al (2002). The expanded LSU sequence dataset ultimately was used to characterize and describe a family for species and genera in the Cryphonectria-Endothia complex of genera. LSU sequences also were supplemented with more variable sequences of the ribosomal ITS region and ß-tubulin genes, to show infrafamilial relationships.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSTAXONOMYDISCUSSIONLITERATURE CITED |
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, 2003; Venter et al 2002; Gryzenhout et al 2004; Myburg et al 2004a, b; Gryzenhout et al 2005a), were included in sequence data analyses (TABLE I). Isolates (CMW 10779–10781) that represented the undescribed genus from S. aromaticum in Indonesia (Myburg et al 2003) also were included (TABLE I).
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and Zhang and Blackwell (2001) were included. These isolates included Cryptodiaporthe corni (Wehm.) Petr. (AR 2814), and isolates of C. macrospora (Tak. Kobay. & Kaz. Itô) M.E. Barr (AR 3444) and C. nitschkei (G.H. Otth) M.E. Barr (AR 3433) from Siberia, Russia. These were kindly provided for additional analyses by Drs A.Y. Rossman and L.A. Castlebury (Systematic Botany and Mycology Laboratory, USDA-ARS, Beltsville, Maryland). Cryptodiaporthe corni was of interest because it grouped separately from other Cryptodiaporthe Petr. species in the Gnomoniaceae clade, including the type species Cryptodiaporthe aesculi (Fuckel) Petr. (Castlebury et al 2002).
The isolate referred to as E. eugeniae (Nutman & F.M. Roberts) J. Reid & C. Booth (CBS 534.82), sequenced by Zhang and Blackwell (2001) and used by Castlebury et al (2002), was acquired from the Centraalbureau voor Schimmelcultures (CBS), Utrecht, Netherlands. It was necessary to include this isolate because it did not group with the isolate of Chr. cubensis, even though it represents a previous synonym of C. cubensis (Hodges et al 1986, Micales et al 1987, Myburg et al 2003). The isolate of C. havanensis (Bruner) M.E. Barr (CBS 505.63) used in the study of Castlebury et al (2002) has been shown (as E40 or CMW 10453) to represent Chr. cubensis (Hodges et al 1986, Micales et al 1987, Myburg et al 2004a).
Isolates in this study (TABLE I
) are maintained in the culture collection (CMW) of the Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, South Africa. A representative subset of these isolates not in other internationally recognized culture collections is stored in the culture collection of the Centraalbureau voor Schimmelcutures, Utrecht, Netherlands (TABLE I). Background information pertaining to other isolates included in the phylogenetic analyses can be found in the studies of Zhang and Blackwell (2001) and Castlebury et al (2002).
PCR amplification and sequencing.— –
Isolates were grown in malt extract broth (20 g/L Biolab malt extract). DNA was extracted from the mycelium following the method used by Myburg et al (1999). To characterize the isolates of Cryptodiaporthe corni (AR 2814), C. macrospora (AR 3444), C. nitschkei (AR 3433) and E. eugeniae (CBS 534.82), the ITS1, 5.8S and ITS2 regions of the rRNA operon as well as two regions within the ß-tubulin gene were amplified with previously described methods (Myburg et al 1999, 2002).
DNA from isolates representing key species of Cryphonectria, Endothia, Chrysoporthe, Rostraureum, Amphilogia and the undescribed fungi from Indonesia (TABLE I) was used to amplify a region of the LSU rDNA gene. Primers pairs ITS3 (White et al 1990) and LR3 (Vilgalys and Hester 1990) were used. The reaction mix used the same reagents and concentrations as those used for the ITS and ß-tubulin reactions. PCR conditions were 95 C for 3 min (denature), 30 cycles of 95 C for 30 s (denature), 56 C for 45 s (anneal), 72 C for 1 min (elongation) and a final elongation step of 72 C for 4 min. Amplification products were purified with a QIAquick PCR Purification Kit (QIAGEN GmbH, Hilden, Germany) and used directly as templates in subsequent sequencing reactions.
Sequencing reactions were as specified by the manufacturers of the ABI PRISMTM Dye Terminator Cycle Sequencing Ready Reaction Kit (Perkin-Elmer, Warrington, UK). Nucleotide sequence data were generated with an ABI PRISM 3100TM automated DNA sequencer (Perkin-Elmer, Warrington, UK). The primer pairs used in the respective sequencing reactions were: ITS1 and ITS4 (amplifying the ITS region), Bt1a and Bt1b (amplifying ß-tubulin region 1), Bt2a and Bt2b (amplifying ß-tubulin region 2), LS1 and LR3 (amplifying LSU rDNA).
Raw sequence data generated for the respective gene regions were edited with Sequence Navigator version 1.0.1 (Perkin-Elmer Applied BioSystems Inc., Foster City, California) software, exported to PAUP* (Phylogenetic Analysis Using Parsimony [*and other methods]) version 4.0b8 (Swofford 1998) and aligned to available sequence datasets. Subsequent phylogenetic analyses were executed with PAUP*.
Analyses of LSU rDNA sequences.— –
The subset of isolates used to generate large subunit ribosomal RNA sequence data for this study included 12 taxa (TABLE I). These sequences were aligned with the 650 bp dataset of Castlebury et al (2002) obtained from TreeBase (study accession number S815). This dataset was shown to be sufficient to define the various lineages within the Diaporthales, although higher bootstrap values were obtained with a larger dataset (Castlebury et al 2002). Only key taxa representing each lineage and the type species of genera were retained in the dataset. LSU sequences for additional species from other studies also were added to this database. These included species in the Schizoparme-complex derived from van Niekerk et al (2004); species of Harknessia, Apoharknessia and Wuestneia derived from Lee et al (2004); representatives of the Togniniaceae (Réblová et al 2004) and a second Crypto. corni isolate sourced from Zhang and Blackwell (2001).
Phylogenetic trees were generated by parsimony and distance analyses. LSU sequence data were deposited in GenBank (TABLE I) and the datamatrix in TreeBase (S1487, M2671). Gaps were treated as characters in the parsimony analyses using the NEWSTATE option in PAUP* and missing in the distance analyses. Parsimony was inferred from TBR swapping algorithms with MULTREES inactive and trees randomly added (100 reps). Uninformative characters were excluded and remaining characters were reweighted according to their consistency indices (CI) to reduce the number of trees. A 50% consensus bootstrap analysis was performed with the heuristic search modified by using no branch swapping with the MULTREES option turned off and only 10 random repeats (Castlebury et al 2002). This was done because bootstrap analysis was inordinately extensive using the parameters defined to generate the trees and could not run to completion (Castlebury et al 2002). For the distance analyses a neighbor joining tree was generated with the Tamura-Nei (TrNef+I+G) model (Tamura and Nei 1993) with invariable sites (I), gamma distribution (G) and equal base frequencies was used (I = 0.5726; G = 0.7028; rate matrix 1.0000, 4.2834, 1.0000, 1.0000, 8.9689, 1.0000). These parameters were determined with Modeltest version 3.5 (Posada and Crandall 1998).
The probabilities of branches occurring were tested with Bayesian inference employing the Markov chain Monte Carlo (MCMC) algorithm (Larget and Simon 1999). The program MrBayes version 3.1.1 (Huelsenbeck and Ronquist 2001) was used with these parameters: number of generations = 1 000 000, sample frequency = 100, number of chains = four (one cold, three hot) and a burn-in of 1000. Four independent analyses were run, with one having 3 000 000 generations. The likelihood model and settings were the same as for the distance methods, as determined by Modeltest.
Analyses of ITS rDNA and ß-tubulin sequences.— –
The ribosomal DNA (ITS1, 5.8S, ITS2) and ß-tubulin sequence data generated in this study were added to already published sequences of other species (TABLE I) using the TreeBase sequence matrix (study accession number S1128, matrix accession number M1935) from Myburg et al (2004a). Two isolates of Diaporthe amibigua Nitschke were used as outgroup because they are more distantly related members of the same order. The datasets for the two regions of the genome sequenced were subjected to a partition homogeneity test (Farris et al 1994) to ascertain whether they could be combined in a single sequence dataset in the phylogenetic analyses. Phylogenetic analyses were done with both parsimony and distance methods. All the sequence characters were unordered. Gaps were treated as characters with the NEWSTATE option in parsimony analyses and as missing in distance analyses. Parsimony was inferred from heuristic searches, with tree-bisection-reconnection (TBR) and MULTREES options (saving all optimal trees) effective and trees added randomly (100 repetitions). Uninformative characters were excluded, and remaining characters were reweighted according to their individual CI to reduce the number of trees.
The distance analysis was done with the neighbour joining method and the general time reversal model (GTR +I+G) (Rodríguez et al 1990), with G = 1.3390, I = 0.4877, base frequency 0.1929, 0.3348, 0.2315, 0.2409 and rate matrix 0.9638, 2.7348, 1.2919, 1.5236, 3.3995, 1.00. This model was chosen based on likelihood ratio tests performed by Modeltest version 3.5 (Posada and Crandall 1998). The confidence levels of the tree branch nodes were determined by a 1000-replicate bootstrap analysis showing values greater than 70%. Bayesian analyses were made with the same parameters and methodology as those in the LSU analysis, with the exception that the distance settings were those determined for this particular dataset by Modeltest and the long run had 5 000 000 generations. GenBank accession numbers of sequences generated in this study as well as those from previous phylogenetic studies are listed (TABLE I). The resulting dataset and trees have been deposited in TreeBase as S1487, M2671.
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RESULTS |
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) showed the same lineages, although relationships between the lineages differed. Reasonably high bootstrap values (85%) were obtained for the Cryphonectria-Endothia complex in the distance analyses, although bootstrap values were below 50% for parsimony analyses. Bayesian analyses showed the same groupings and topology than those obtained in the distance and parsimony analyses with high posterior probability values for the different families (FIG. 2). This included the clade representing the Cryphonectria-Endothia complex (posterior probability 74%).
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) was similar to the trees presented by Castlebury et al (2002), although the present study included a substantially greater number of taxa representing the Cryphonectria-Endothia complex. These included at least six genera. Inclusion of these additional taxa did not affect the structure of the Cryphonectria-Endothia group, which remained a distinct lineage. Other lineages in the phylogram represent the families Gnomoniaceae, Melanconidaceae, Valsaceae, Diaporthaceae, Togniniaceae and the Schizoparme complexes as previously defined (Zhang and Blackwell 2001, Castlebury et al 2002, Réblová et al 2004).
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).
Analyses of ITS rDNA and ß-tubulin sequences.— –
The dataset consisted of 32 taxa of which the two D. ambigua isolates were defined as outgroup. Results generated with the PHT analyses (P = 0.306) indicated that the rDNA and ß-tubulin sequence datasets were significantly congruent and that they could be combined; this is in accordance with the trees of similar topology and having strong support generated from the separate datasets. The aligned ribosomal DNA sequence dataset (566 characters) consisted of 315 constant, 12 parsimony uninformative and 239 parsimony informative characters (g1 = –0.7185 after exclusion of uninformative characters), and the ß-tubulin alignment (955 characters) consisted of 538 constant, 21 parsimony uninformative and 396 parsimony informative characters (g1 = –0.535 after exclusion of uninformative characters). The combined dataset consisted of 1521 characters. The heuristic search resulted in a single most parsimonious tree (tree length = 1223.91668, CI = 0.741, RI = 0.905). Both the distance and Bayesian analyses showed the same grouping of isolates. Exclusion of ambiguously aligned sequences representing the introns in the ß-tubulin alignment and the ITS1 regions also resulted in similar trees. The tree obtained with distance analyses was chosen for presentation (FIG. 2).
Phylogenetic analyses based on the ITS region and ß-tubulin sequences, showed the same clades as those observed in previous studies (Myburg et al 2003, 2004a, Myburg et al b; Gryzenhout et al 2005a). Endothia, Cryphonectria, Chrysoporthe, Amphilogia and Rostraureum formed distinct and well supported clades, while the isolates representing an apparently undescribed genus from clove in Indonesia also formed a discrete group (FIG. 2). The isolate of E. eugeniae (CBS 534.82) included in the study of Zhang and Blackwell (2001), grouped in the clade representing this undescribed genus (bootstrap 100%). The isolates of C. nitschkei and C. macrospora from Russia included in the study of Castlebury et al (2002), grouped with Japanese isolates of C. nitschkei in the Cryphonectria clade (bootstrap 100%, posterior probability 100%). The isolate of Crypto. corni did not reside in any of the clades resulting from the phylogenetic analyses but grouped closely to them.
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TAXONOMY |
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showed that Cryphonectria, Endothia and closely related genera represent a distinct monophyletic lineage in the Diaporthales. This has also been shown based on analyses of a larger LSU sequence data as the one used in this study (Castlebury et al 2002) and it is supported by easily defined morphological characteristics. These findings provide strong justification for the establishment of a new family in the Diaporthales.
Genera in this complex have distinct orange stromatic tissue in the teleomorph state and usually in the anamorph state, which is different from any other species in the Diaporthales. Members of this group also can be distinguished from other taxa in the Diaporthales by the purple discoloration of the stromatic tissue in 3% KOH and a yellow reaction in lactic acid (Castlebury et al 2002). This discoloration is due to pigments in the stromatic tissue, often responsible for the orange colour, and that is also produced in culture (Roane 1986, Castlebury et al 2002).
Endothia and Cryphonectria represent the oldest and best known names in the group representing these and related fungi. They thus would represent an ideal foundation for a new family name. In the case of Endothia, E. gyrosa, the type species of the genus, is well characterized morphologically and based on DNA sequences (Shear et al 1917, Roane 1986, Micales and Stipes 1987, Venter et al 2002, Myburg et al 2004a). However the type specimen of this species is old and only anamorph structures are present on it (Shear et al 1917). An epitype for this species is thus needed (Myburg et al 2004a) and it is not presently available.
The typification of Cryphonectria recently has been revised. This was necessary because of nomenclatural problems with Cryphonectria gyrosa as type (Myburg et al 2004a, Gryzenhout et al 2005c) and the fact that this fungus belongs in Amphilogia (Myburg et al 2004a; Gryzenhout et al 2005b, c). Hence Cryphonectria has been conserved with a new type, C. parasitica (Gryzenhout et al 2005c). Due to the importance and notoriety of this fungus, Cryphonectria represents an appropriate choice as type for a new family. This description thus is provided:
Cryphonectriaceae Gryzenh. & M. J. Wingf., fam. nov.
Ascostromata subimmersa vel superficialia, textura stromatica aurantiaca, collis peritheciorum cum textura stromatica aurantiaca vel fusconigra tectis. Asci fusoidei. Ascosporae ellipsoideae, fusoideae vel cylindricae, non septatae vel usque ad multiseptatae, hyalinae. Conidiomata eustromatica, subimmersa vel superficialia, aurantiaca vel fusconigra. Cellulae conidiogenae phialidicae. Conidia perparvula, ovoidea vel cylindrica, non septata, hyalina. Textura stromatica in 3% KOH purpurascit, in acido lactico flavescit.
Ascostromata small to large, erumpent, semi-immersed to superficial, generally with orange stromatic tissue. Perithecia fuscous black to umber, occurring underneath bark surface or superficially in stroma, perithecial necks slender, covered with orange to fuscous-black stromatic tissue. Asci fusoid, aparaphysate, free floating. Ascospores generally ellipsoid to fusoid to cylindrical, aseptate to multiseptate, hyaline. Conidiomata eustromatic, semi-immersed to superficial, pyriform to pulvinate, orange to fuscous black, occasionally occurring in same stroma than perithecia. Conidiogenous cells phialidic, simple or branched. Conidia minute, generally ovoid to cylindrical, aseptate, hyaline. Stromatic tissue turns purple in 3% KOH and yellow in lactic acid.
Typus genus: Cryphonectria (Sacc.) Sacc., Syll. Fung. 17:783. 1905.
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DISCUSSION |
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, which treated a large number of genera in the Diaporthales to delimit family relationships within the order. The aim of the present study was to focus specifically on genera in the Cryphonectria-Endothia complex and to include additional isolates, particularly new genera that recently have been assigned to this group. In this way we were able to further test the unique nature of the group and to show that it represents a distinct phylogenetic lineage, for which we have now provided family status.
Genera residing in the newly defined Cryphonectriaceae clearly can be set aside from other families in the Diaporthales based on DNA sequence data, particularly for the LSU region. Their unique nature also can be recognized based on a number of morphological features such as the formation of orange stromata and pigments in the stromatic tissue or in culture (Roane 1986) that can be tested with unique color reactions in KOH and lactic acid (Castlebury et al 2002). This is similar to the classifications of the Nectriaceae within the Hypocreales, where one of the distinguishing characteristics of taxa in this family is similar color reactions in KOH and lactic acid (Rossman et al 1999).
In this study problems were experienced with low bootstrap support for the Cryphonectriaceae in parsimony analyses. Similar low bootstrap support also was shown in parsimony analyses presented by Castlebury et al (2002). These authors however showed conclusively that the branch separating the Cryphonectria-Endothia complex from the other lineages was well supported based on additional distance and Bayesian analyses and a longer DNA sequence dataset. We have confirmed this in our study, where support for the clade representing the Cryphonectriaceae was adequately high based on distance and Bayesian analyses.
Analyses of the variable ITS region and ß-tubulin genes in the present study have shown that isolates of Crypto. corni (AR 2814), C. macrospora (AR 3444) and E. eugeniae (CBS 534.82) used in the studies of Zhang and Blackwell (2001) and Castlebury et al (2002) represent taxa other than those assigned to them. Thus the E. eugeniae isolate was shown to group together with isolates representing an undescribed genus from clove in Indonesia (Myburg et al 2003). This isolate does not represent Chr. cubensis, of which E. eugeniae is a synonym to (Hodges et al 1986, Myburg et al 2003). The isolate of C. macrospora from Russia represents C. nitschkei (Myburg et al 2004b), confirming observations of Vasilyeva (1998) that C. nitschkei occurs in Russia, not only in China and Japan (Myburg et al 2004b).
In the present study the isolate of Crypto. corni treated by Castlebury et al (2002) did not group with any of the isolates of Cryphonectria, Endothia, Chrysoporthe, Amphilogia or Rostraureum or with the isolates from Indonesia that represent an undescribed genus. The fungus however does have a position in the Cryphonectriaceae based on the LSU sequence data and its orange/yellow stromatic tissue that turns purple in KOH and yellow in lactic acid (Redlin and Rossman 1991, Castlebury et al 2002). This fungus appears to represent an undescribed genus in the Cryphonectriaceae because its morphology does not correspond with any of the genera currently known for this family (Myburg et al 2004a; Gryzenhout et al 2005a, b). For instance conidiomata of the anamorph Myxosporium nitidum Berk. & Curtis are fully immersed in the bark and emerge through lenticels as orange, subspherical pycnidia (Redlin & Rossman 1991). More detailed studies with additional isolates and specimens of this fungus would be required before a name can be provided for it.
The new family Cryphonectriaceae defined in this study includes some of the most serious tree pathogens in the world. Notable examples are the causal agent of chestnut blight C. parasitica (Anagnostakis 1987) and Chr. cubensis, which is one of the most serious pathogens of plantation-grown Eucalyptus spp. (Wingfield 2003). Many other members of the family are also pathogens. For example R. tropicale causes cankers on Terminalia spp. (Gryzenhout et al 2005a), although it does not appear to have a large ecological impact. It is likely that additional genera will be discovered that reside in the Cryphonectriaceae, as illustrated by the characterization of the Crypto. corni isolate in this study. The description of a new family encompassing Chrysoporthe, Cryphonectria, Endothia and allied genera should aid identification and taxonomic studies on these fungi.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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1 Corresponding author. E-mail: Marieka.Gryzenhout{at}fabi.up.ac.za
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LITERATURE CITED |
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