Occurrence of Phytophthora cinnamomi in the Rhizosphere of Declining Leucadendron elimense subsp. salteri in

ABSTRACT

Phytophthora cinnamomi is a destructive invasive plant pathogen reported from more than 5000 hosts and across all continents except Antarctica. In South Africa, P. cinnamomi poses a substantial threat to native flora, particularly members of the Proteaceae. This pathogen has been detected in diverse settings on hosts within this family, and, of especial concern, in natural populations of species under a high threat of extinction. In this study, P. cinnamomi was detected in a population of Leucadendron elimense subsp. salteri located in a nature reserve. This plant population has experienced a severe decline in recent years. Two plants collected for laboratory analysis exhibited severe collar lesions and had lost most their root system due to root rot, fitting with symptoms typically associated with P. cinnamomi infection in susceptible hosts. Samples were processed, and the presence of P. cinnamomi was confirmed morphologically and molecularly from the rhizosphere soil of both plants. There is an urgent need to mitigate the impacts of P. cinnamomi in South Africa, in particular by expediting the regulatory evaluation of potential treatments.