Molecular characterisation of selected ophiostomatoid fungi

[摘要] English: The ophiostomatoid fungi are found worldwide on a wide variety of substrates. Thegroup is economically important due to the pathogenicity of some species onimportant crops and trees. The success of these fungi as plant pathogens is undoubtlyrelated, 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 ofrhamnose in the cell wall, led us to believe that Ophiostoma polonicum is a typicalspecies of Ceratocystis s.str. Partial sequence data from the rDNA operon presentedin chapter two of this thesis, confirmed the placement of O. polonicum in Ceratocystiss.str. I have, therefore, suggested that the name Ceratocystis polonica should be usedfor this fungus in future and that the reported Leptographium anamorph was mostprobably a contaminant.In chapter three, I have attempted to resolve the question concerning the occurrence ofboth Sporothrix and Chalara anamorphs in Ceratocystis autographa. No culturesexist for the type of C. autographa, although a type specimen shows the presence oftwo distinct and taxonomically unrelated anamorphs. Cultures identified as C.autographa, isolated from Juniperus needles are very different to the original niche ofthe fungus and have caused great confusion. Through sequencing the LTS1, ITS2 and5.8S regions of the rDNA operon of these cultures and comparing them with keyspecies, I have shown that these cultures probably have no connection to C.autographa. I have also concluded that they are atypical of Chalara and shouldreside in a new genus to be named Xenochalara.The last chapter of this thesis relates to an unusual Leptographium species, isolatedprimarily from the bark beetle Hylurgops palliatus. The fungus has reasonably largeconidia 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. guttulatusfor it. This thesis includes three research studies pertaining to diverse questions that haveplaqued the taxonomy of Ceratocystis sensu lato. Problems have been resolvedprimarily using sequencing of the Internal Transcribed Spacer regions of the rDNAoperon. Many additional problems remain in this group of fungi and I feel optomisticthat approaches similar to those presented here will lead to resolving them in comingyears.

[发布机构] University of the Free State