Molecular characterisation of selected ophiostomatoid fungi

Abstract

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.

Afrikaans: Die ophiostomatoid fungi kom wêreldwyd voor en word op 'n wye verskeidenheid van substrate aangetref. Die groep het 'n groot invloed op die ekonomie weens die patogenesiteit van sekere spesies vir belangrike gewasse en bome. Die sukses van hierdie fungi as plantpatogene is gedeeltelik toe te skryf aan hul assosiasie met insekte. veral baskewers. Die teenwoordigheid van 'u Chalara anamorf, sensitiwiteit vir sikloheksimied en die afwesigheid van ramnose in die selwand, het ons laat besluit dat Ophiostoma polonicum 'n tipiese spesie van Ceratocystis s.str. is. Die plasing van 0. polonicum in die genus Ceratocystis s.str, word verder bevestig deur 'n basisopeenvolging studie van 'n gedeelte van die ribosomale DNA operon. Ek het dus voorgestel dat die naam Ceratocystis polonica vir hierdie fungus in die toekoms gebruik word. Die Leptographium anamorf was moontlik 'n kontaminant. In hoofstuk drie het ek onderneem om die kwessie omtrent die voorkoms van beide 'n Sporothrix en 'n Chalara anamorf in Ceratocystis autographa, op te los. Geen herbarium materiaal van die tipe vir C. autographa is beskikbaar. Kulture wat as C. autographa geidentifiseer is, is vanaf die naalde van Juniperus geïsoleer en het weens die verskil m habitat groot verwarring in die taksonomie veroorsaak. Basisopeenvolging bepaling van die ITS 1, ITS2 gebiede asook die 5.8S geen van die rDNA operon van hierdie kulture en die vergelyking daarvan met ander sleutel spesies het gewys dat hierdie kulture moontlik geen verwantskap met C. autographa het nie. Ek het ook die gevolgtrekking gemaak dat hierdie spesies nie tipies van Chalara is nie en dus in 'n nuwe genus, Xenochalara, geplaas moet word. Die laaste hoofstuk van die tesis handeloor Leptographium spesies wat hoofsaaklik vanaf die baskewer, Hylurgops palliatus versamel is. Die fungus het redelik groot konidia en 'n moontlike verwantskap met Leptographium penicillatum as L. penicillatum f.sp. palliati is vermoed. Met die vergelyking van basisopeenvolgings van hierdie fungus met L. penicillatum en ander sleutel spesies, is hierdie fungus as afsonderlik bewys. Ons het dus 'n volledige beskrywing van hierdie fungus gedoen en ook die nuwe naam, L. guttulatus. voorgestel. Hierdie tesis bevat drie navorsing studies handelend oor 'n verskeidenheid vrae met betrekking tot die taksonomie van Ceratocystis sensu lato. Probleme is hoofsaaklik opgelos deur basisopeenvolging bepaling van die ITS gebiede van die rDNA operon. Baie addisionele probleme wat nog in die taksonomie van Ceratocystis s.l. voorkom kan deur die benaderings in hierdie studie gebruik, opgelos word.