Colletotrichum diseases of Proteaceae

[摘要] ENGLISH ABSTRACT: This thesis consists of four chapters that present research findings on Colletotrichumdiseases associated with Proteaceae worldwide. The first chapter is a review of literatureregarding the taxonomy and histology of Colletotrichum species associated with Proteaceae. Theliterature is not restricted to Proteaceae hosts, as information regarding Colletotrichum onProteaceae is very limited.In chapter two, Colletotrichum spp. associated with proteaceous hosts growing in variousparts of the world were identified based on morphology, sequence data of the internal transcribedspacer region (ITS-I, ITS-2), the 5.8S gene, and partial sequences of the B-tubulin gene. Fourspecies of Colletotrichum were associated with Proteaceae. Colletotrichum gloeosporioides wasisolated from Protea cynaroides cultivated in South Africa and Zimbabwe and from aLeucospermum sp. in Portugal, but is known to occur worldwide on numerous hosts. A recentlydescribed species, C. boninense, was associated with Zimbabwean and Australian Proteaceae, butalso occurred on a Eucalyptus sp. in South Africa. This represents a major geographical and hostextension for the species, and a description of the African strains is provided. Colletotrichumcrassipes was represented by a single isolate obtained from a Dryandra plant in Madeira.Colletotrichum acutatum was isolated from Protea and Leucadendron in South Africa as well asfrom other proteaceous hosts occurring elsewhere. Colletotrichum acutatum f. sp. hakea wasisolated from Hakea in South Africa. In chapter three, pathogenicity of these Colletotrichum species to certain proteas wasestablished, relative aggressiveness of the different species tested and host response to them werecompared as well as the effect that wounding had on host response. From the results obtained itis concluded that C. acutatum and C. gloeosporioides are the primary pathogens associated withColletotrichum leaf necrosis, and C. acutatum is the main cause of anthracnose and stem necrosisof Proteaceae in South Africa.A histological study was performed in chapter four in response to the findings from theprevious chapter. The behaviour of two C. acutatum isolates (one originating from Protea andthe other from Hakea, C. acuataum f.sp. hakea) was studied on inoculated Protea leaf surfacesusing light and scanning electron microscopy. Colletotrichum acutatum from Protea formedmelanised appressoria on the leaf surface, whereas C. acutatum from Hakea formed very lownumbers of both melanised and unmelanised appressoria. Most of the appressoria formed by C.acutatum from Protea were formed on the cell junctions and on the periclinal walls of theepidermal cells. From this study it is clear that C. acutatum f. sp. hakea is not a pathogen ofProtea. Consequently the current use of this isolate as a biological control agent of Hakea inSouth Africa poses no threat to indigenous Protea species. Colletotrichum acutatum from Protea(although closely related to C. acutatum f. sp. hakea), is a pathogen of Protea, which wasconfirmed by histological observations.In conclusion, the present study has shown that several species of Colletotrichum areassociated with diseased Proteaceae. These species differed in their pathogenicity andaggressiveness when inoculated onto certain protea cultivars. These differences could bepartially explained by examining the behaviour of C. acutatum on the leaf surface. It is clear, however, that the distribution of the different species, their aggressrveness on differentProteaceae and their modes of infection needs to be investigated further. This work provides abasis for future research on the long-term effective management of these pathogens in fynbosproduction.

[发布机构] Stellenbosch University