Phylogenetic relationships and population dynamics of Calonectria

[摘要] ENGLISH SUMMARY: This dissertation is presented as a collection of separate publications and an amountof redundancy has thus been unavoidable. Although several species are newlydescribed they are not effectively published and will thus be formally published inscientific journals. There were two main objectives:I. To investigate the variability and mating compatibility of species andpopulations, in order to contribute to the systematics of Calonectria.II To identify loci that would be useful for DNA sequence comparisons in thisgenus and to present a reliable phylogeny of Calonectria and other closely relatedhypocrealean taxa.In the introductory review a synopsis of the current knowledge regarding thetaxonomy and life cycle of Calonectria and Cylindrocladium spp. is presented. Theimportance of these pathogens are noted, as well as the problems related toidentifying them. Aspects regarding specific species complexes and topics arediscussed in more detail in the following chapters.The morphological and phylogenetic variation was investigated for the Cy.candelabrum species complex in Part 2. DNA sequence comparisons of theribosomal 5.8S gene and flanking ITS1 and ITS2 spacers were employed in order todetermine whether mating incompatibility and general morphology was supported bymolecular evidence. Although only small differences were found these proved to beconsistent and resulted in the recognition of Galonectria scoparia (anamorphCylindrocladium candelabrum), and the description of three new species, namelyCalonectria pallciramosa (anamorph Cyfindrocladium pauciramosum), Calonectriainsularis (anamorph Cylindrocladium insulare) and Calonectria mexicana (anamorphCylindrocladium mexicanum).The Cyfindrocladium scoparium cultures studied in Part 3 were isolated from severalhosts in the U.S.A. Isolates were mated in all combinations, and one successfulmating was selected to establish whether recombination occurred. RAPD andmating type data of parental isolates and progeny confirmed Cy. scoparium to have aheterothallic mating system. Furthermore, to determine the phylogeny of Cy.scoparium with several morphologically similar Cylindrocladium spp., DNA sequences of the ribosomal 5.8S gene and the flanking internal transcribed spacers(ITS), as well as part of the high mobility group (HMG) box (forming part of the MA T-2 mating type gene) and the β-tubulin gene, were analysed. Maximum parsimonyyielded concordant trees for all three data sets. These data supported themorphological and biological species concepts proposed for Cy. scoparium andother, similar, small-spored Cylindrocladium spp.Part 4 represented an investigation into the mating compatibility and mating typedistribution of populations of Cy. pauciramosum. This enabled the determination ofthe effective population for the different areas studied. A sample collected over aperiod of six years, reflecting a number of locations in South Africa were found have1: 1 mating type ratio, as expected in a random mating population. However, themating type ratio was found to be significantly different in single nursery populations.In the South African nursery, the MAT-1 mating type was dominant, while the MAT-2was more common in other samples obtained from nurseries in Italy and the U.S.A..This was consistent with one or more founder effects. The high percentage ofhermaphrodites also suggested that recent introductions had occurred in nurseries inItaly and the U.S.A. In addition to this, DNA sequence comparisons of the β-tubulingene was used to investigate variation below species level in Cy. pauciramosum. Allisolates from South Africa, Australia, U.S.A. and a group from Italy had identicalsequences. A second group with identical sequences were found in the Italiansample. In addition to this, variation was found between all isolates from Brazil,Colombia and Mexico. Some of these base pairs were shared between the Southand Central American isolates as well as isolates of Cy. candelabrum. This pointstowards a speciation event in South or Central America.After investigating variation below species level, this study was also expanded togeneric level. In Part 5 information obtained in the preceding chapters culminated ina phylogeny of all known species in Calonectria and Cylindrocladium based on DNAsequence comparisons of the β-tubulin gene. Many clades, containing small numbersof isolates were strongly supported by bootstrap. However, relationships betweenthese clades were often ambiguous. A number of phylogenetic placements based onDNA data did not always agree with preconceived morphological relationships. Twolarge groupings were evident and both contained small-spored, one-septate species.The only morphological character that correlated with DNA based phylogenies wasvesicle shape of the anamorph. Finally, in Part 6, the generic phylogeny was investigated. In order to obtain ageneric phylogeny a subset of Calonectria species was selected, as well as isolatesfrom other genera, closely related to Calonectria. All of these genera were originallydescribed under the broad concept of Nectria sensu lato. A gene tree phylogeny,based on β-tubulin was presented for selected nectriaceous genera with anamorphsbearing cylindrical macroconidia. Based on molecular data and the distinctanamorph genera, new teleomorph genera were proposed for Gylindrocladiella(Nectricladiella), Gliocladiopsis (Glionectria) and Xenocylindrocladium(Xenocalonectria). Ca/onectria was also found to form a monophyletic lineage. Eightspecies of Cylindrocladiella were recognised, with two having teleomorphs inNectricladiella, namely N. camelliae (Ce. microcylindrica) and N. infestans (Ce.infestans).This study concluded that the current morphological species concepts inCylindrocladium and its Calonectria teleomorphs can comprise several biological aswell as phylogenetic species. The use of mating testers in this study was shown toprovide a powerful tool to separate morphologically similar, but genetically isolatedspecies. The biological and morphological species also agreed with the phylogeneticconcepts used, but only vesicle shape were found to define phylogenetic clades.However, phylogenetic species concepts based on DNA sequences data obtainedfrom genomic regions such as the β-tubulin and MA T-2 genes and additional areaswill become increasingly important for further taxonomic studies in Calonectria andrelated genera.

[发布机构] Stellenbosch University