Thesis (Ph.D.(Botany))--University of Pretoria, 2003. / Includes bibliographical references.

published_or_final_version / Botany / Master / Master of Science

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Thesis (Master of Conservation Science)--Cape Peninsula University of Technology, 2018. / Introduction pathways of fungal pathogens in South Africa are far less quantified in the literature than those for plants, animals and human infectious diseases. Phytopathogens continue to be introduced to South Africa via several pathways at an unprecedented rate. A number of these species pose a significant threat to South African ecosystems and biodiversity. Despite this, fungal pathogens could also be beneficial when they are used as bio-control agents to control alien invasive plant species. Nevertheless, recent studies revealed pathogens are most likely to be studied after they have caused a detrimental impact on the environment. Invasive fungal pathogens, such as Phytophthora cinnamomi (Oomycota) do not only pose a threat to native species of the family Proteaceae but could also potentially be bio-control agents for emerging alien plant invaders. In this thesis, firstly, I review current knowledge of phytopathogenic fungi introduction pathways in South Africa; secondly, I aim to understand the importance of fungi in limiting plant invasions using Banksia as a case study in the Cape Floristic Region. In chapter two I investigate introduction pathways and dispersal vectors that facilitate the spread of fungal pathogens. I compiled comprehensive list of fungal pathogens in South Africa, and evaluated the dispersal vectors and introduction pathways for each species. I found fifty five casual species, three naturalised species, six invasive species and thirty six pathogens for which invasion status was not classified due to insufficient data. Agriculture is responsible for the introduction of most fungal pathogens in South Africa. Wind was identified to be the prominent dispersal vector facilitating the spread of pathogens. I conclude that knowing introduction pathways of pathogens and their dispersal vectors will assist in developing quarantine protocols that could improve bio-security. Lastly, I provide recommendations for the national invasive microbe species list. In chapter three the study investigates the variability in mortality rate of Banksia species in the Cape Floristic. Species abundance was calculated across known Banksia populations in the Cape Floristic Region to determine survival and mortality rates. Soil and leave samples were taken from Banksia plants to evaluate potential microbial pests that were present. Also, acetone leaf extracts of twelve Banksia species were screened for antimicrobial activity against P. cinnamomi (Oomycota). Lastly, a post-border risk assessment was conducted for 14 Banksia species− present in South Africa − using the Australian Weed Risk Assessment protocol, to evaluate potentially invasive species. The results indicated that survival and mortality rate varied across species; I found the two invasive species, B. integrifolia and B. ericifolia to have the highest survival rate. Phytophthora cinnamomi was the most prominent isolated fungal pathogen sampled from Banksia species roots. The detection of antifungal activities in the minimum inhibitory concentration (MIC) bioassay provided evidence that some Banksia species (B. ericifolia, B. integrifolia, B. hookeriana and B. formosa) have antimicrobial chemical constituents that could possibly inhibit infection and colonisation by P. cinnamomi. The weed risk assessments conducted on Banksia species showed five species pose a high risk of invasion while seven species required further evaluation. I conclude that P. cinnamomi could potentially regulate invasive Banksia species such as B. speciosa with minimal antimicrobial activity against the pathogen. I recommend an in-situ and ex-situ inoculation trials of Banksia species against P. cinnamomi to be conducted to evaluate pathogenicity, under different watering regimes since the pathogens proliferation is favoured by soils that are high in moisture. I present the main conclusions from this thesis in chapter four and provide recommendations for management and invasive species legislation.

Blackleg, caused by L. maculans, is of major economic importance in the canola growing areas of Australia. The aim of this research was to gain information about factors affecting the epidemiology of blackleg in south - eastern Australia. The effect of temperature on a number of aspects of the life cycle of L. maculans was studied in a controlled environment. Germination of ascospores was greater on agar and cotyledons than on leaves, on susceptible cultivars than resistant cultivars, and at 15 and 20 °C than at 5 and 10 °C. Elongation of germ tubes was greater at higher than lower temperatures and generally greater on cotyledons than on leaves of the cultivars after incubation for 24 h at 10 - 20 ° C. Temperature had a greater influence than plant organ or cultivar on ascospore germination and the elongation of germ tubes. Temperature, wetness duration, cultivar and leaf position ( leaves 1 - 3 ) influenced the incubation period of L. maculans on canola. Ascospores infected six canola cultivars over 10 - 20 ° C following leaf wetness duration of 16 - 72 h. Incubation period ( from inoculation to the appearance of first lesions ) was generally shorter at higher temperatures and following longer wetness periods. Incubation period decreased with increasing leaf age, regardless of the blackleg - resistance rating of the cultivars. Pseudothecia developed on naturally infested canola stubble incubated at 5 - 20 ° C under continuous wetness and a 12 h photoperiod. The time taken for pseudothecia to mature after harvest, ranged from 58.3 days at 5 ° C to 22.2 days at 15 ° C. Fewer pseudothecia developed on stubble incubated in darkness at 15 ° C than in light. Pseudothecia took longer to mature when wetness was interrupted than continuous. More ascospores were released at 20 ° C than 5 - 15 ° C, although peak sporulation occurred earlier at 5 - 10 ° C. Discharge of ascospores continued for 8 h at 5 - 10 ° C, for 10 h at 15 ° C, and for 12 h at 20 ° C. The effect of burial of infested canola stubble in sand and field soil ( in pots ) on pathogen survival, pathogenicity and stubble - associated fungi was studied over 13 months in ambient conditions. The isolation frequency of L. maculans from stubble decreased by 63.3 % after 13 months of burial, regardless of soil type. Although the frequency of isolation of L. maculans and Alternaria spp. from stubble decreased over time, that of Stachybotrys chartarum, Fusarium spp. and Coprinus sp. increased substantially over the sampling period. Stubble buried in field soil underwent more decay than in sand over the 13 months. Pseudothecium formation on buried stubble decreased with increasing duration of burial and ceased after 11 months in the field soil and 13 months in sand. The time required for pseudothecia to mature was 25 days for stubble retrieved after one month and 30 days when retrieved 10 months after burial, regardless of soil type. Ascospores from the stubble recovered from burial caused typical Phoma leaf spots on canola over the first 9 months of burial. Over the year, 16 genera of fungi and 12 colony types of bacteria were isolated from the field soil on peptone - rose bengal agar ( PRA ) and on crystal violet agar ( CVA ), respectively. Populations of fungi and bacteria isolated on soil - extract agar were markedly greater than those on PRA and on CVA, respectively. Growth and sporulation of L. maculans on agar media and on infested canola stubble was affected by a variety of fungi obtained from stubble buried in soil or from field soil. Antagonistic activities observed included lysis, deformation, overgrowth and inhibition of L. maculans hyphae, and reduction of pseudothecium density on stubble to one - third or less than that on controls following inoculation with F. equiseti, Gliocladium roseum, Trichoderma aureoviride, Sordaria sp. and an unknown Coelomycete. S. chartarum and Coprinus sp. reduced the mass of canola stubble in vitro. Findings will contribute to a better understanding of blackleg and to the development of more effective control measures. / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2006.

The objectives of this study were: (1) to determine the etiology of bull's eye rot on pears grown in Oregon and Washington; (2) to determine periods of greatest susceptibility of pear wood to canker formation by the fungal pathogens Neofabraea alba and N.perennans; (3) to monitor conidial production in cankers; (4) to determine the timing of fruit infection; and (5) to determine the effect of environmental factors, cultural practices and chemical treatments on the development of bull's eye rot of pears. N. alba, N. perennans and N. sp. nova were identified in isolates obtained from bull's eye rot on pear fruit, using species-specific primers in a PCR reaction. N. alba was also found to be associated with naturally occurring small cankers and pruning stubs on pear trees. Pear trees were inoculated at monthly intervals with mycelia of N. alba and N. perennans to determine susceptibility to canker formation. Susceptibility was highest during autumn and winter months, with larger cankers bearing conspicuous acervuli produced after inoculations from October to February. Small cankers resulted from conidial inoculations with N. perennans on superficially wounded pear branches. Cankers induced after mycelial inoculations sporulated throughout the year with highest amounts of conidia produced from September to December. Pear fruit became naturally infected throughout the growing season, with increasing infection levels close to harvest. Contradictory effects of temperature on bull's eye rot development by N. perennans were observed between 2001 and 2002, where the highest levels of disease were found at 10°C and at 30°C, respectively. Wetness duration did not affect bull's eye rot development, while the concentration of conidia correlated positively with disease development. Over-tree irrigation and late harvest resulted in higher disease levels than under-tree irrigation and early to mid season harvest. The fungicides trifloxystrobin and ziram protected inoculated fruit for about one month, while copper sulfate reduced the sporulation rate of cankers induced by N alba. Thiabendazole applied as a postharvest dip reduced bull's eye rot on inoculated pears. / Graduation date: 2004

Thesis (Ph. D.)--Oregon State University, 2003. / Typescript (photocopy). Includes bibliographical references (leaves 160-173). Also available via the World Wide Web.

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Blackleg, caused by L. maculans, is of major economic importance in the canola growing areas of Australia. The aim of this research was to gain information about factors affecting the epidemiology of blackleg in south - eastern Australia. The effect of temperature on a number of aspects of the life cycle of L. maculans was studied in a controlled environment. Germination of ascospores was greater on agar and cotyledons than on leaves, on susceptible cultivars than resistant cultivars, and at 15 and 20 °C than at 5 and 10 °C. Elongation of germ tubes was greater at higher than lower temperatures and generally greater on cotyledons than on leaves of the cultivars after incubation for 24 h at 10 - 20 ° C. Temperature had a greater influence than plant organ or cultivar on ascospore germination and the elongation of germ tubes. Temperature, wetness duration, cultivar and leaf position ( leaves 1 - 3 ) influenced the incubation period of L. maculans on canola. Ascospores infected six canola cultivars over 10 - 20 ° C following leaf wetness duration of 16 - 72 h. Incubation period ( from inoculation to the appearance of first lesions ) was generally shorter at higher temperatures and following longer wetness periods. Incubation period decreased with increasing leaf age, regardless of the blackleg - resistance rating of the cultivars. Pseudothecia developed on naturally infested canola stubble incubated at 5 - 20 ° C under continuous wetness and a 12 h photoperiod. The time taken for pseudothecia to mature after harvest, ranged from 58.3 days at 5 ° C to 22.2 days at 15 ° C. Fewer pseudothecia developed on stubble incubated in darkness at 15 ° C than in light. Pseudothecia took longer to mature when wetness was interrupted than continuous. More ascospores were released at 20 ° C than 5 - 15 ° C, although peak sporulation occurred earlier at 5 - 10 ° C. Discharge of ascospores continued for 8 h at 5 - 10 ° C, for 10 h at 15 ° C, and for 12 h at 20 ° C. The effect of burial of infested canola stubble in sand and field soil ( in pots ) on pathogen survival, pathogenicity and stubble - associated fungi was studied over 13 months in ambient conditions. The isolation frequency of L. maculans from stubble decreased by 63.3 % after 13 months of burial, regardless of soil type. Although the frequency of isolation of L. maculans and Alternaria spp. from stubble decreased over time, that of Stachybotrys chartarum, Fusarium spp. and Coprinus sp. increased substantially over the sampling period. Stubble buried in field soil underwent more decay than in sand over the 13 months. Pseudothecium formation on buried stubble decreased with increasing duration of burial and ceased after 11 months in the field soil and 13 months in sand. The time required for pseudothecia to mature was 25 days for stubble retrieved after one month and 30 days when retrieved 10 months after burial, regardless of soil type. Ascospores from the stubble recovered from burial caused typical Phoma leaf spots on canola over the first 9 months of burial. Over the year, 16 genera of fungi and 12 colony types of bacteria were isolated from the field soil on peptone - rose bengal agar ( PRA ) and on crystal violet agar ( CVA ), respectively. Populations of fungi and bacteria isolated on soil - extract agar were markedly greater than those on PRA and on CVA, respectively. Growth and sporulation of L. maculans on agar media and on infested canola stubble was affected by a variety of fungi obtained from stubble buried in soil or from field soil. Antagonistic activities observed included lysis, deformation, overgrowth and inhibition of L. maculans hyphae, and reduction of pseudothecium density on stubble to one - third or less than that on controls following inoculation with F. equiseti, Gliocladium roseum, Trichoderma aureoviride, Sordaria sp. and an unknown Coelomycete. S. chartarum and Coprinus sp. reduced the mass of canola stubble in vitro. Findings will contribute to a better understanding of blackleg and to the development of more effective control measures. / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2006.