Molecular characterisation of selected ophiostomatoid fungi

English: The ophiostomatoid fungi are found worldwide on a wide variety of substrates. The group is economically important due to the pathogenicity of some species on important crops and trees. The success of these fungi as plant pathogens is undoubtly related, at least in part, to their association with insects, especially bark beetles. The presence of a Cho/ara anamorph, sensitivity to cycloheximide and the absence of rhamnose in the cell wall, led us to believe that Ophiostoma polonicum is a typical species of Ceratocystis s.str. Partial sequence data from the rDNA operon presented in chapter two of this thesis, confirmed the placement of O. polonicum in Ceratocystis s.str. I have, therefore, suggested that the name Ceratocystis polonica should be used for this fungus in future and that the reported Leptographium anamorph was most probably a contaminant. In chapter three, I have attempted to resolve the question concerning the occurrence of both Sporothrix and Chalara anamorphs in Ceratocystis autographa. No cultures exist for the type of C. autographa, although a type specimen shows the presence of two distinct and taxonomically unrelated anamorphs. Cultures identified as C. autographa, isolated from Juniperus needles are very different to the original niche of the fungus and have caused great confusion. Through sequencing the LTS1, ITS2 and 5.8S regions of the rDNA operon of these cultures and comparing them with key species, I have shown that these cultures probably have no connection to C. autographa. I have also concluded that they are atypical of Chalara and should reside in a new genus to be named Xenochalara. The last chapter of this thesis relates to an unusual Leptographium species, isolated primarily from the bark beetle Hylurgops palliatus. The fungus has reasonably large conidia and has been thought to be related to Leptographium penicillatum as L. penicillatum f.sp. palliati. Through sequence data comparisons of this fungus with L. penicillatum and other key species, we have shown that it is distinct. We have, therefore, provided a full description and have also proposed the name L. guttulatus for it. This thesis includes three research studies pertaining to diverse questions that have plaqued the taxonomy of Ceratocystis sensu lato. Problems have been resolved primarily using sequencing of the Internal Transcribed Spacer regions of the rDNA operon. Many additional problems remain in this group of fungi and I feel optomistic that approaches similar to those presented here will lead to resolving them in coming years.