Phytophthora diversity in the Cape Floristic Region

Thesis (PhD)--University of Pretoria, 2020.

The biodiversity in the Cape Floristic Region of South Africa faces many threats from anthropogenic sources such as the trade associated with our globalized economy. Aggressive plant pathogens in the genus Phytophthora are of particular concern because of their capacity to invade and change plant communities and their frequent dissemination via global trade. The fact that South Africa has a developing economy with many socioeconomic challenges, the capacity to monitor the abundance of plants imported for pests and pathogens is largely inadequate. Consequently, low cost methods to enhance post-border surveillance for the emergence of Phytophthora species are critically needed in South Africa. Therefore, the major aims of the research conducted in this thesis were to: 1) reveal the diversity and potential threats of Phytophthora species already present within the Cape Floristic Region, and 2) provide information and an example of an approach to enhance the biosecurity with public engagement in South Africa. Through independent sampling and a newly developed citizen science program, this body of work revealed the presence of seventeen described Phytophthora species, one informally described Phytophthora species, and three putative hybrids. Seven of these Phytophthora species were not previously known to occur in South Africa. The work also revealed a relationship between the invasion of P. cinnamomi and the health of trees and evidence is provided for dissimilarity between invaded and non-invaded plant communities. In addition, through a synthesis of modern Phytophthora species descriptions and a diversity study in botanical gardens, it was possible to provide evidence for the importance of surveying urban environments. Then as a means to demonstrate the potential of public engagement to enhance biosecurity, the findings from activities in Cape Citizen Science have been summarized. In this case it was possible to show that nine of the Phytophthora species were recovered only because of citizen participation. Cumulatively, this thesis has advanced the base of knowledge regarding the presence and consequences of Phytophthora species in the Cape Floristic Region. In this sense, they also provide valuable information and a model system to enhance biosecurity in South Africa as well as in countries with similar economies.

Microbiology and Plant Pathology

PhD

Unrestricted