Browsing by Author "Schoch, Conrad Lamoraal"
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- ItemPhylogenetic relationships and population dynamics of Calonectria(Stellenbosch : Stellenbosch University, 1999-12) Schoch, Conrad Lamoraal; Crous, P. W.; Wingfield, M. J.; Wingfield, B. D.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant pathology.ENGLISH SUMMARY: This dissertation is presented as a collection of separate publications and an amount of redundancy has thus been unavoidable. Although several species are newly described they are not effectively published and will thus be formally published in scientific journals. There were two main objectives: I. To investigate the variability and mating compatibility of species and populations, in order to contribute to the systematics of Calonectria. II To identify loci that would be useful for DNA sequence comparisons in this genus and to present a reliable phylogeny of Calonectria and other closely related hypocrealean taxa. In the introductory review a synopsis of the current knowledge regarding the taxonomy and life cycle of Calonectria and Cylindrocladium spp. is presented. The importance of these pathogens are noted, as well as the problems related to identifying them. Aspects regarding specific species complexes and topics are discussed 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 the ribosomal 5.8S gene and flanking ITS1 and ITS2 spacers were employed in order to determine whether mating incompatibility and general morphology was supported by molecular evidence. Although only small differences were found these proved to be consistent and resulted in the recognition of Galonectria scoparia (anamorph Cylindrocladium candelabrum), and the description of three new species, namely Calonectria pallciramosa (anamorph Cyfindrocladium pauciramosum), Calonectria insularis (anamorph Cylindrocladium insulare) and Calonectria mexicana (anamorph Cylindrocladium mexicanum). The Cyfindrocladium scoparium cultures studied in Part 3 were isolated from several hosts in the U.S.A. Isolates were mated in all combinations, and one successful mating was selected to establish whether recombination occurred. RAPD and mating type data of parental isolates and progeny confirmed Cy. scoparium to have a heterothallic 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 parsimony yielded concordant trees for all three data sets. These data supported the morphological and biological species concepts proposed for Cy. scoparium and other, similar, small-spored Cylindrocladium spp. Part 4 represented an investigation into the mating compatibility and mating type distribution of populations of Cy. pauciramosum. This enabled the determination of the effective population for the different areas studied. A sample collected over a period of six years, reflecting a number of locations in South Africa were found have 1: 1 mating type ratio, as expected in a random mating population. However, the mating 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-2 was 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 of hermaphrodites also suggested that recent introductions had occurred in nurseries in Italy and the U.S.A. In addition to this, DNA sequence comparisons of the β-tubulin gene was used to investigate variation below species level in Cy. pauciramosum. All isolates from South Africa, Australia, U.S.A. and a group from Italy had identical sequences. A second group with identical sequences were found in the Italian sample. In addition to this, variation was found between all isolates from Brazil, Colombia and Mexico. Some of these base pairs were shared between the South and Central American isolates as well as isolates of Cy. candelabrum. This points towards a speciation event in South or Central America. After investigating variation below species level, this study was also expanded to generic level. In Part 5 information obtained in the preceding chapters culminated in a phylogeny of all known species in Calonectria and Cylindrocladium based on DNA sequence comparisons of the β-tubulin gene. Many clades, containing small numbers of isolates were strongly supported by bootstrap. However, relationships between these clades were often ambiguous. A number of phylogenetic placements based on DNA data did not always agree with preconceived morphological relationships. Two large groupings were evident and both contained small-spored, one-septate species. The only morphological character that correlated with DNA based phylogenies was vesicle shape of the anamorph. Finally, in Part 6, the generic phylogeny was investigated. In order to obtain a generic phylogeny a subset of Calonectria species was selected, as well as isolates from other genera, closely related to Calonectria. All of these genera were originally described under the broad concept of Nectria sensu lato. A gene tree phylogeny, based on β-tubulin was presented for selected nectriaceous genera with anamorphs bearing cylindrical macroconidia. Based on molecular data and the distinct anamorph genera, new teleomorph genera were proposed for Gylindrocladiella (Nectricladiella), Gliocladiopsis (Glionectria) and Xenocylindrocladium (Xenocalonectria). Ca/onectria was also found to form a monophyletic lineage. Eight species of Cylindrocladiella were recognised, with two having teleomorphs in Nectricladiella, namely N. camelliae (Ce. microcylindrica) and N. infestans (Ce. infestans). This study concluded that the current morphological species concepts in Cylindrocladium and its Calonectria teleomorphs can comprise several biological as well as phylogenetic species. The use of mating testers in this study was shown to provide a powerful tool to separate morphologically similar, but genetically isolated species. The biological and morphological species also agreed with the phylogenetic concepts used, but only vesicle shape were found to define phylogenetic clades. However, phylogenetic species concepts based on DNA sequences data obtained from genomic regions such as the β-tubulin and MA T-2 genes and additional areas will become increasingly important for further taxonomic studies in Calonectria and related genera.