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II. Species with Hyaline or Lightly Pigmented Perithecial Walls; Subhymenial Layer Often Thickened and Pigmented
Only five New Zealand species have been studied. As no characteristic conidial form has been found to be common to all species in this section, each species is discussed separately.
Nectria peziza (Tode) Fr.
No conidial form was found among perithecia in field collections. Single spore cultures produced only intercalary chlamydospores which, formed in chains of four to six, were globular, thick walled, 5–8μ diameter Perithecia develop in cultures six weeks old.
Nectria cyathea Dingley.
No conidial form was found among perithecia in field collections. Cultures are slow growing, isabelline, floccose, sometimes zoned. Arthrospores are formed among ropelike.
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Text-fig. 2.—Fig. 1.—Conidial forms of N. ralfsii. Fig. 2.—Conidial forms of N. otagensis Fig. 3.—Conidial forms of N. macrostoma.
mycelium. Intercalary chlamydospores were also present, more or less globose, 8–15μ. in diameter. Perithecia form in cultures 6–8 weeks old.
Nectria ralfsii Berk. & Br.
Erumpent sporodochia covered with dark translucent masses of conidia occur among clusters of immature perithecia. From single ascospore isolations developed a white floccose culture White pulvinate sporodochia were formed which, when mature, became translucent, greenish-black with catenulated conidia. Conidiophores form a superficial layer up to 200μ long; they are penicillately branched, terminating in phialides 15–20 × 2–3μ. Conidia are broadly elliptical, 10–18 × 7–9μ, often with a distinct papilla and pigmented, thickened walls Intercalary chlamydospores were present among mycelium of the sporodochia (Text-fig. 2, 1). Rilestone (1941) noted “that Mr. E. W. Mason regarded this conidial form as identical with Sphaeropsis henriquesii Thumen, but that as the conidia are not borne in pycnidia the fungus cannot be classified as a Sphaeropsis; for the present it should be known as the conidial form of N. ralfsii” Sections of young sporodochia show a structure similar to the superficial layer of Dendrodochium. Conidiophores are branched penicillately, and often swollen below septa, while branches terminate in phialides from which pigmented, not hyaline, conidia are catenulated.
Nectria macrostoma Berk & Curt.
In field collections clusters of perithecia are aggregated around bases of the synnemata, stalks of the synnemata are dark coloured, whereas conidial heads are pale salmon and translucent; sporodochia are present. In cultures synnemata 0.5 mm long are formed in small clusters of 2—5 arising from small byssoid stromata. When immature the dark stalks terminate in penicillately branched hyaline conidiophores, each branch ending in a typical subulate phialide. In mature fructifications, terminal branches become compacted together and slimy conidia, catenulated from phialides, adhere together to form globose, pale salmon translucent heads.
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Conidia are hyaline, globose or broadly elliptical, 2–6 × 1.5–3 5μ. Intercalary chlamydospores are present in the mycelium (Text-fig. 2, 3). This conidial stage conforms with the imperfect form-genus Graphium Corda, as defined in its limited sense by Mason (1937).
Nectria otagensis Currey ex Lindsay.
On some young stromata immature perithecia surround large cavities filled with orange translucent conidial masses. Superficially these cavities appear as labrynthiform pycnidia, but neither a true ostiole nor a distinct wall is present; hyphae from the stroma converge around them, and from this layer of tissue arise regularly arranged phialides to form a compact layer lining each cavity. Conidia are catenulated, adherent, fill the central cavity, and exude as an orange, waxy mass. Conidia are unicellular, elliptical, sometimes more or less bacilliform, hyaline, 2–5 × 1.5–2μ (Text-fig. 2, 2). This conidial stage is typical of the form genus Aschersonia Mont., usually associated with Hypocrella Sacc., a genus in the Clavicipitaceae. In cultures conidia are catenulated from phialides which form lateral branches on aerial hyphae; sometimes hyphae are compacted into a slimy stroma. Conidia are unicellular, allantoid, 3–4 × 0.75–1.5μ.