Additional specimens: Ireland, County Waterford. Isolated from Owenashad River in a temperate mixed coniferous and deciduous forest. Collected: R. O’Hanlon, July 2017; CBS 147243 = P17-76A, P17-76, P17-76B. July 2018; P18-110B.

Sporangia, hyphal swellings and chlamydospores (Fig 4)—Sporangia of N. irlandica were infrequently observed on solid V8A and were produced abundantly after 24 hr in non-sterile soil extract. Sporangia were usually borne terminally (Fig 4A–4H and 4J) or very rarely laterally on unbranched undulating sporangiophores or less frequently in dense sympodia of 2–4 sporangia (Fig 4J). Mature sporangia were non-papillate (Fig 4A–4F and 4I) and had a conspicuous opaque plug formed inside the sporangiophore close to the sporangial base which averaged 2.7 ± 0.9 μm (Fig 4A–4G and 4I). They were partially caducous breaking off just below the basal plug (Fig 4I). Sporangial shapes ranged from ovoid or elongated ovoid (28.5%; Fig 4A–4C and 4G), ellipsoid (29.3%; Fig 4E and 4I) and limoniform (41.5%; Fig 4F and 4I) to obpyriform (<1%; Fig 4D). Sporangia with special features like lateral attachment of the sporangiophore (27.1%; Fig 4B, 4C and 4I), a vacuole (<1%; Fig 4C) or undulating sporangiophores (32.1%) occurred in all isolates. Sporangia proliferated exclusively externally, usually immediately below the sporangial base (Fig 4C and 4J). Sporangial dimensions of five isolates averaged 47.1 ± 6.1 × 28.5 ± 3.4 μm (overall range 28–74.2 × 15.9–46.6 μm and range of isolate means 44.4–51.1 × 23.3–30.7 μm). The length/breadth ratio averaged 1.7 ± 0.2 with a range of isolate means of 1.5–1.9 (Table 2). Zoospores were discharged through an exit pore 5.8–14.9 μm wide (av. 10.6 ± 1.8 μm; Fig 4H and 4J). Zoospores were limoniform to reniform whilst motile, becoming spherical (av. diam = 9.6 ± 1.3 μm) on encystment. Cysts germinated directly. Intercalary, globose to subglobose or limoniform, sometimes catenulate hyphal swellings, measuring 12.8 ± 3.8 μm, were infrequently formed on sporangiophores by all isolates. Globose (99.9%; Fig 4K–4P) or less frequently pyriform, limoniform or irregular (<1%) chlamydospores were produced terminally (Fig 4K, 4N and 4O) or intercalary (Fig 4L, 4M and 4P) and measured 42.0 ± 4.0 μm (Table 2). They often had radiating hyphae which usually showed intense and dense branching close to the chlamydospore (Fig 4N and 4O). Hyphal swellings were also observed (Fig 4Q and 4R). Oogonia, oospores and antheridia—All five isolates of N. irlandica examined were self-sterile and did not form gametangia in single culture or in pairings with A1 and A2 tester strains of P. ramorum and P. cinnamomi. Colony morphology, growth rates and cardinal temperatures (Figs 5 and 6)—Colonies of the five tested isolates of N. irlandica on V8A and CA were appressed to submerged and had either rosaceous or faintly striate to uniform patterns. On PDA colonies of all isolates were appressed and dense felty with a more or less clear rosaceous pattern and irregular margins (Fig 5). All five isolates of N. irlandica included in the temperature-growth test had similar growth rates and cardinal temperatures. The maximum and lethal growth temperatures were 25 and 30°C, respectively (Table 2, Fig 6). The average radial growth rate at the optimum temperature of 20°C was 2.1 ± 0.3 mm/d (Table 2, Fig 6).

Ireland, County Wicklow, isolated from a tributary of the Ow River in a temperate, planted coniferous forest, R. O’Hanlon, 05 December 2014 (CBS H-24576 holotype, dried culture on CA, herbarium Westerdijk Fungal Biodiversity Institute, CBS 147242 = Pr13-109, ex-type culture). ITS and cox1 sequences GenBank MW364574 and MW367172, respectively.