Phytophthora virginiana sp. nov., a high-temperature tolerant species from irrigation water in Virginia

Isolates belonging to a previously unknown species of Phytophthora were recovered from irrigation reservoirs at several ornamental plant nurseries in Virginia. Morphological features of this species include abundant lateral chlamydospores in clarified V8 juice agar and carrot agar and terminal, ovoid to obpyriform, nonpapillate and noncaducous sporangia in soil water extract. All tested isolates are silent A¹ mating type. They did not produce any sexual structures but induced A² mating type testers of P. cinnamomi and P. cryptogea to produce gametangia. Sequence analysis of the internal transcribed spacer (ITS) region confirmed that this species belongs to the high-temperature tolerant cluster within Phytophthora clade 9. Its ITS sequence differs from those of its two closest relatives, P. hydropathica and P. parsiana, by >26 bp. Based on these morphological, physiological, and molecular characteristics, we recognise it as a new species, described here as Phytophthora virginiana.