Phytophthora kernoviae Brasier, Beales & S.A. Kirk (2005) was first observed in Cornwall, southwest England in 2003. The new species was described in 2005. It causes leaf lesions on rhododendron and stem lesions on European beech in gardens and woodlands in the UK and Ireland. Other trees and shrubs are also affected. The pathogen appears to match isolates recovered in New Zealand from a diseased cherimoya orchard in 2006 and soil isolates recovered previously from a native kauri forest and a radiata pine plantation. P. kernoviae has also been isolated from fallen leaves of Drimys winteri and streams in a native South American forest. Etymology: ‘Kernow’, the old name for Cornwall.
Sporangia (34-52 x 19-31 µm, mean range ca 38.5-45.5 x 22.3 x 27 µm) papillate and caducous, formed occasionally on carrot agar (CA) in the light, produced abundantly on CA plugs in nonsterile pond water or soil leachate, ovoid, limoniform to asymmetric or ‘mouse-shaped’, most with a conspicuous vacuole, pedicel length 5-19 µm, borne on sympodially branched sporangiophores. Hyphae sometimes denticulate or tuberculate. Chlamydospores not observed. Colonies in dark on CA largely submerged with small central area of aerial mycelium, with alternating rings of mycelium in diurnal light. Homothallic, gametangia abundant on CA after 10 d. Oogonia diameter 21-28 µm (mean 23.5-25.5 µm), often with tapered stalks. Oospores 19-25 µm (mean 21.1-22.5 µm), plerotic, wall thickness 3.5-5 µm (mean ca. 3.5 µm). Antheridia amphigynous, commonly 10-14 x 9-12 µm. Compared to UK isolates described above (Brasier et al., 2005), New Zealand isolates are reported to grow somewhat slower at 20° C and have a few small differences in the size of oogonia, sporangia, and pedicel length (Ramsfield et al. 2009).