First record of the white root rot fungus Dematophora necatrix on indigenous South African trees

Abstract

The soilborne fungus Dematophora (=Rosellinia) necatrix and causal agent of white root rot, has a wide host range that includes many tree species of economic importance. The pathogen has a worldwide distribution, including reports from commercial orchards in South Africa since the 1970s. During tree health surveys conducted as part of a sentinel plant project, we detected the pathogen on two symptomatic individuals from the indigenous South African tree species Diospyros whyteana and Noronhia foveolata subsp. major. Observed symptoms included wilting and root rot, with characteristic white mycelium present under the bark. Dematophora necatrix was isolated from both hosts and its identity confirmed by sequencing two gene regions (ITS and actin). Pathogenicity was confirmed through inoculation tests under semi-controlled conditions by inoculating the soil with bamboo sticks colonized with the fungus. Plants of both species developed similar symptoms to those observed naturally, and the fungus was successfully recovered from all symptomatic plants. This is the first record in South Africa of D. necatrix on indigenous species and outside of commercial orchards. Given the environmental threat posed we recommend the fungus is considered for regulation in South Africa.