A diverse range of Phytophthora species from botanical gardens in South Africa, including the novel Clade 5 species, Phytophthora mammiformis sp. nov.

Abstract

The genus Phytophthora contains many destructive and globally important plant pathogens. In the last decade, targeted sampling efforts have resulted in a dramatic increase in the number of known species, as well as a better understanding of their global distribution. Routine activities undertaken in botanical gardens, combined with great numbers of local and international visitors, place botanical gardens at risk to the accidental introduction and establishment of pathogens such as Phytophthora spp. In this study, the occurrence of Phytophthora was investigated in two botanical gardens in the KwaZulu- Natal Province of South Africa. Symptomatic collar and stem tissues were collected, and root and rhizosphere soil samples were taken from trees exhibiting symptoms of decline. Standard baiting techniques and direct plating of symptomatic tissues revealed the presence of seven species of Phytophthora residing in four phylogenetic clades. Five of these species, P. cinnamomi, P. citrophthora, P. multivora, P. parvispora and the informally designated taxon Phytophthora sp. stellaris were known to be present in South Africa and P. aquimorbida was recorded for the first time. Of these, P. citrophthora represented a novel host-pathogen association causing bleeding cankers on indigenous Celtis africana. A multilocus phylogenetic analysis based on ITS, βtub, cox1 and hsp90 sequences showed the presence of an undescribed species belonging to the Phytophthora ITS Clade 5. This species is described here as Phytophthora mammiformis sp. nov. This study highlights the importance of monitoring botanical gardens for the detection and discovery of pathogens and emphasises their value as sites for the discovery of novel host-pathogen associations.