Ophiostomatoid fungi and their insect associates on Eucalyptus trees in Australia and South Africa

Abstract

The eucalypt plantation industry in South Africa is an important source of revenue for the country. Eucalypt trees have been planted in the country for more than 200 years, as ornamentals, sources of fuel and construction wood, and more recently also for the production of paper and rayon, amongst other uses. The planting of eucalypts in South Africa has contributed to the development of many forestry industries. It has also reduced the logging of indigenous forests. Eucalypts in South Africa are, however, affected by numerous pests and pathogens. These include native South African pests and pathogens, as well as those introduced from other countries. Of the pathogens, those commonly reffered to as pathogenic Ophiostomatoid fungi, particularly species of Ceratocystis and Ophiostoma are probably the best known. In recent years, some fungal species in the genera Ceratocystis and Ophiostoma have emerged as important threats to plantation forestry globally and it is critical to understand these fungi in order to reduce their future impact on eucalypts. In this dissertation, Ophiostomatoid fungi that infested eucalypt trees in Australia and South Africa, that were also identified from nitidulid beetles that visit these hosts, were identified using morphology and DNA sequence data. As a foundation for the studies in the dissertation chapter one provided a review of the literature pertaining to insects in the Nitidulidae and their association with fungi including Ceratocystis spp. In chapters two and three, four new taxa, C. tyalla, C. corymbiicola, O. tasmaniense, O. undulatum as well as four previously known species, C. pirilliformis, Ophiostoma quercus, O. tsotsi, Pesotum australiae were identified from eucalypts in Australia. The four new taxa were not pathogenic to E. grandis seedlings in greenhouse inoculation studies. In the last two chapters, seven Ceratocystis and five Ophiostoma spp. were identified from various Eucalyptus spp. and including some isolated from nitidulid beetles in South Africa. The Ceratocystis spp. included two new taxa (C. salinaria, C. decipiens) and five known species, C. eucalypticola, C. pirilliformis, C. moniliformis, C. oblonga, C. savannae. The Ophiostoma spp. included two new taxa of the Ophiostoma stenoceras-Sporothrix schenkii species complex (O. candidum, O. fumeum) and three known species (O. quercus, O. tsotsi, O. tasmaniense). The new taxa of Ceratocystis and Ophiostoma identified in South Africa were not pathogenic to E. grandis seedlings in a greenhouse inoculation studies. Most of the fungi identified were encountered on some nitidulid insects, and four of these fungi where found in both Australia and South Africa. This suggests an intercontinental movement of Ceratocystis and Ophiostoma, probably mediated by insects, in particular nitidulid beetles.