Two new Phytophthora species from South African Eucalyptus plantations

Abstract

A recent study to determine the cause of collar and root rot disease outbreaks of cold tolerant Eucalyptus species in South Africa resulted in the isolation of two putative new Phytophthora species. Based on phylogenetic comparisons using the ITS and β-tubulin gene regions, these species were shown to be distinct from known species. These differences were also supported by robust morphological characteristics. The names, Phytophthora frigida sp. nov. and Phytophthora alticola sp. nov. are thus provided for these taxa, which are phylogenetically closely related to species within the ITS clade 2 (P. citricola, P. tropicali and P.multivesiculata) and 4 (P. arecae and P. megakarya), respectively. Phytophthora frigida is heterothallic, and produces stellate to rosaceous growth patterns on growth medium, corraloid hyphae, sporangia with a variety of distorted shapes and has the ability to grow at low temperatures. Phytophthora alticola is homothallic and has a slower growth rate in culture. Both P. frigida and P. alticola are pathogenic to Eucalyptus dunnii. In pathogenicity tests, they were, however, less pathogenic than P. cinnamomi, which is a well-known pathogen of Eucalyptus in South Africa.