Seed-borne fungi of the afromontane tree species Podocarpus falcatus and Prunus africana in Ethiopia

This thesis is comprised of four studies regarding seed-borne fungi of the afromontane forest trees, Podocarpus falcatus (Thunb. Mirb.) and Prunus africana (Hook. F.) Kalkman, in Ethiopia. Based on morphology and molecular data from the rDNA (ITS) region, a diverse group of mainly Ascomycota, some Basidiomycota and a few Zygomycota were identified. Phylogenetic analysis of the ITS sequences revealed several clades differentiated according to the host. Some of these fungi were previously reported as seed-borne pathogens from other parts of the world. More fungi were isolated from P. falcatus than from P. africana. Four Botryosphaeria spp., three of them from P. falcatus and one from P. africana were identified. The Botryosphaeria sp. from P. africana was a previously undescribed species and named Diplodia rosulata sp. nov. One of the three Botryosphaeria spp. from P. falcatus was identified as B. parva while the other two were previously undescribed Botryosphaeria spp. with Diplodia and Dothiorella anamorphs. Botryosphaeria parva was previously identified as a major cause of Botryosphaeria stem canker on Eucalyptus plantations in Ethiopia and elsewhere. The implications of the occurrence of B. parva both on native and exotic tree species were discussed. Based on seed and seedling inoculation tests on P. falcatus, five categories of fungi ranging from strong pathogens to germination promoters were identified. Among the tested fungi, Fusarium oxysporum and Polyporus sp. were strongly pathogenic and caused both seed rotting and seedling damping-off, while Diaporthe sp. Po21 and Diaporthe sp. Po84 promoted seed germination. Dual culture tests among seed-borne fungi of P. falcatus on 2 % malt extract agar resulted in deadlock or replacement interactions. Co-inoculation of seeds with two germination promoters and six pathogenic isolates resulted in improved germination in some of the combinations. Bioassay tests with HPLC fractions of culture filtrates of the two germination promoting Diaporthe spp. indicated antifungal activity against F. oxysporum and Ulocladium chartarum. From these studies it was concluded that different groups of fungi could be associated with seeds of forest trees. There are still many undescribed fungal species that may impact forest establishment and development. Therefore, more investigations are necessary in these areas.