Melanconis pacifica Jaklitsch & Voglmayr, 2020

Jaklitsch, Walter M. & Voglmayr, Hermann, 2020, The genus Melanconis (Diaporthales), MycoKeys 63, pp. 69-117 : 69

Melanconis pacifica Jaklitsch & Voglmayr sp. nov. Fig. 12

Diagnosis.

This species is characterised by its occurrence on Alnus rubra and α-conidia, which are wider and darker than those of M. marginalis and differ by a different shape and absence of a light band from those of M. alni .

Type material.

Holotype. Canada, British Columbia, Sidney, off Jura, on Alnus rubra , 26 May 2000, M.E. Barr 1021A (DAOM 230637; ex-type culture CBS 109744; isotype BPI 748446).

Etymology.

For its occurrence in the Pacific region of western North America.

Description.

Asexual morph: Conidiomata 0.7-2.1 mm diam., visible as dark brown to blackish spots, acervular, subperidermal, scattered, discrete, rarely two confluent, pulvinate to conical, consisting of an erumpent central or eccentric, circular or elliptic to fusoid, flat or convex disc 0.2-1.3 mm diam., whitish, yellowish to reddish-orange when young, becoming concealed by ejected conidia and internally a narrow central or eccentric, whitish to yellowish stromatic column sometimes fraying out laterally and a dark ring-like periphery containing conidia. Conidia becoming discharged through a mostly slit-like rupture of the disc, forming dark brown to black, up to 0.7 mm high masses or tendrils. Conidiophores densely aggregated forming palisades, up to ca. 50 µm long, arising from a yellowish, nearly pseudoparenchymatous tissue of compacted hyphae, either consisting solely of conidiogenous cells or of a stout main axis with few side branches and a terminal whorl of 2-4 more or less vertical conidiogenous cells, hyaline to yellowish. Conidiogenous cells mostly 11-32 × (2-)2.5-3.3(-3.5) μm, annellidic, more or less cylindrical, hyaline, turning brown with age, forming simultaneously two types of conidia on top. Conidia dimorphic, α- conidia (8.8-)10.5-12.5(-15.5) × (5-)6.5-7.7(-8.8) µm, l/w (1.2-)1.4-1.8(-2.7) (n = 615), oval to ellipsoid, dark brown, with a distinct basal abscission scar; β- conidia (6.2-)8.2-12.5(-18.5) × (2-)2.3-3(-3.6) µm, l/w (1.7-)3-4.9(-7.6) (n = 103), oblong to cylindrical, straight or curved, sometimes sigmoid or kidney-shaped to subellipsoid, hyaline, turning dilute brownish with age, typically containing two subterminal groups of minute guttules, with a distinct basal abscission scar.

Culture: Colony on MEA circular, first hyaline, turning white and later brownish in spots or patches, with stellate margin and radial stripes; black conidiomata forming along the stripes. Odour indistinct.

Additional materials examined

(all on/from Alnus rubra ). Canada, British Columbia, Sidney, Bazan Bay, 28 May 1995, M.E. Barr (DAOM 220988); Victoria, 26 km N of Campbell River, 50.1262N, 125.3084W, 2 Jan 1989, T.N. Sieber (DAVFP 24981, dried culture PFC-071 only); Caycuse, W shore of Cowichan Lake, 48.8810N, 124.4321W, 24 Oct 1988, T.N. Sieber (DAVFP 24980, dried culture PFC-068 only); Gordon Head, C. Dorworth’s property, 48.4396N, 123.3380W, 4 Jun 1988, C. Dorworth (DAVFP 24973, dried culture PFC-043 only); East Sooke, 48.4377N, 123.7436W, 29 Jun 1948, W.G. Ziller (DAVFP 3092); Nanaimo, DeCourcy Island, 49.0641N, 123.7732W, 1 Jun 1988, C. Dorworth (DAVFP 24974, dried culture PFC-047 only); Parksville, NW Bay, 3.1 km W of M&B office, 49.3238N, 124.1479W, 13 Jul 1988, C. Dorworth (DAVFP 24975, dried culture PFC-050 only); Port Renfrew, Sombrio Beach, 48.5229N, 124.2866W, 4 Nov 1988, C. Dorworth (DAVFP 24977, dried culture PFC-053 only); Revelstoke, Jordan River, gravel pit S of the river, 48.4356N, 124.0140W, 24 Oct 1988, C. Dorworth (DAVFP 24978, dried culture PFC-055 only); ibid., 24 Oct 1988, T.N. Sieber (DAVFP 24979, dried culture PFC-067 only); Sooke, East Sooke Park, Babbington Trail, 48.3485N, 123.6073W, 9 Sep 1988, C. Dorworth (DAVFP 25029, dried culture PFC-054).

Notes.

The description is largely based on DAOM 220988 due to good development of conidiomata. However, we select DAOM 230637 as the holotype, because DNA data are only available for this specimen. Microscopic data of the two specimens are identical. This species is currently only known as an asexual morph. One specimen from Victoria (DAVFP 3092) contains also an immature sexual morph, which corresponds to Melanconis alni superficially. Barr apparently identified her collections as M. marginalis because the latter was, at that time, considered to be the only alnicolous species occurring in North America ( Jensen 1984), which also occurs on A. rubra ( Sieber et al. 1991). However, the conidia of the latter species are longer, more fusoid, have a larger l/w ratio and are lighter in colour than those of M. pacifica . α-conidia of M. pacifica and M. alni are virtually identical in size. Those of the latter, however, have a different shape, a median light band and a more greyish-brown colour. Remarkably, Wehmeyer (1941) mentioned a collection from the American Pacific region (Oregon) which had conidia resembling Melanconium sphaeroideum , a synonym of M. alni . Sieber et al. (1991) included 10 isolates from Alnus rubra , sampled in British Columbia, that they identified as Melanconium apiocarpum , another synonym of M. alni (see above), based on conidial size and shape. Their measurements and, in particular, their illustration (fig. 2a) of α-conidia fully agree with M. pacifica . The isozyme patterns of Sieber et al. (1991) revealed high similarities, but also diagnostic differences between the isolates from European A. glutinosa and Canadian A. rubra , which is in agreement with the close phylogenetic relationship between M. alni and M. pacifica . Our morphological re-investigations of the isolates of Sieber et al. (1991), which are kept as dried cultures at DAVFP (see specimens cited above), confirmed that they represent M. pacifica .

In DAOM, two additional specimens, labelled Melanconis marginalis collected by Barr in the same area, are extant, DAOM 227727 and DAOM 227345. These specimens, however, do not contain M. pacifica , but the sexual morph of a Diaporthe sp.

Figures

Figure 12. Melanconis pacifica. Asexual morph a-d conidiomata in face view e conidioma in cross section f conidioma in vertical section g-k conidiophores (g with both conidial types, note annellations in right conidiophore in k) l-r α-conidia s-z β-conidia a-k, n-p, z DAOM 220988 l, m, r-y holotype DAOM 230637 q isotype BPI 748446 g-o, r-z in 3 % KOH. Scale bars: 300 µm (a-f), 30 µm (g), 10 µm (h-k), 5 µm (l-z).