Ophiostoma species from hardwood sources in South Africa

[摘要] English: The ophiostomatoid fungi are an economically important group of fungi, known for their ability to stain sapwood and cause tree diseases. In recent years, certain species in the group have also been considered as potential biological control agents in the pulp and paper industry. White mutants of species like Ophiostoma piliferum utilize pitch, which can cause problems in the pulping process, in freshly cut pulpwood chips. At the same time, other degrading fungi are out-competed. The first chapter of the thesis reviews the development, application, benefits and possible problems, of these biological control products. The possible application of such products in the South African pulp industry is also considered. One of the major concerns for the application of a biological control product such O. piliferum in South Africa, is the fact that it consists of a living fungus originating in the USA. A survey was, therefore, conducted to determine whether the fungus occurs in South Africa. The typical niche for O. piliferum is stained logs, lumber, and pulpwood chips. Isolates resembling O. piliferum were obtained from both exotic and indigenous wood sources. Based on morphology, these isolates could be separated into three groups, which resembled the descriptions of O. stenoceras, O. pluriannulatum, and O. piceae, respectively. For correct identification, the South African isolates had to be compared with herbarium material and authentic isolates from other parts of the world. The comparative taxonomic studies for the three groups of fungi form the basis of Chapters 4, 5 and 6 of this thesis. The taxonomic history of the genera Ophiostoma and Ceratocystis is complicated and confused. Published literature on the two genera, with the emphasis on Ophiostoma and its associated anamorph genera, is reviewed in Chapter 3. This serves as a background for the four following chapters of the thesis. Ribosomal DNA sequencing confirmed that one group of South African isolates is the same as O. stenoceras isolates from the Northern Hemisphere. Similar isolates from Colombia, Uruguay, and Kenya, were also included in the study and represent the first reports of O. stenoceras from these countries. Ophiostoma albidum, O. abietinum and O. nigrocarpum, all closely resemble O. stenoceras morphologically. Our sequence data show that O. albidum should be considered a synonym of O. stenoceras, and that O. abietinum is a synonym of O. nigrocarpum, which is a species distinct from O. stenoceras. For the past three decades, O. stenoceras has been considered the teleomorph of Sporothrix schenckii, the human pathogen. Our results, however, showed that rDNA sequences of the two species are significantly different, confirming that S. schenckii is a distinct species. The group of South African isolates resembling O. pluriannulatum, differed from this Northern Hemisphere species in that isolates have light brown perithecial bases and clubshaped ornamental hyphae on the perithecial bases. Similar isolates were obtained from Equador and Indonesia. Ribosomal DNA sequence data made it possible to distinguish between the two groups, and the Southern Hemisphere fungus is, therefore, described as a new species, Ophiostoma tropieale. Ophiostoma piceae and O. querei are virtually indistinguishable based on morphology, but hosts, rDNA sequences, and mating compatibility, can be used to separate the two species. By applying these criteria, the South African isolates resembling O. piceae obtained in the survey (Chapter 2), grouped with O. querei. Also included in the O. querei group were isolates from Brazil and Japan. One South African isolate, however, were identified as O. floccosum, representing the first report of this fungus from South Africa. The presence and distribution of species of the O. piceae complex in the Southern Hemisphere, are also discussed in Chapter 6. In recent literature, some confusion has emerged regarding the use of the name O. querei as opposed to 0. quercus. The last chapter of the thesis presents a brief review of the Latin and nomenclatural guidelines applicable in this particular case. The conclusion is that both names are grammatically acceptable. However, following the Code of Botanical Nomenclature, O. querei should be given preference. The work presented in this thesis contributes significantly to our understanding of the ophiostomatoid fungi, and in the greater context, biodiversity, in South Africa. Ribosomal DNA sequencing was successfully applied in conjunction with traditional taxonomic criteria to distinguish between species. However, many new questions arose from these results, especially regarding the phylogeny of Ophiostoma spp. with Sporothrix anamorphs. The results obtained from this study, will serve as the foundation for future research addressing these questions.

[发布机构] University of the Free State