Helicoon subglobosum, 2018

Goh, Teik-Khiang & Kuo, Chang-Hsin, 2018, A new species of Helicoön from Taiwan, Phytotaxa 346 (2), pp. 141-156 : 145-148

Helicoön subglobosum Goh & C.H. Kuo , sp. nov. FIGURE 1−4

MycoBank: MB 822429

Etymology: subglobosum , referring to the subglobose shape of the conidia.

Diagnosis: Differs from other Helicoön species in having large subglobose conidia which are borne singly on very short conidiophores.

Colonies on natural substratum dark-brown, somewhat glistening, effuse. Mycelium partly immersed but mostly superficial, consisting of branched hyphae and short conidiophores bearing conidia; superficial hyphae ca 3.5−5.5 μm wide, pale yellowish-brown, smooth, branched, closely septate, slightly constricted at the septa which are 11.7−18 μm apart. Conidiophores macronematous, mononematous, cylindrical, erect, straight, arising as short branches more or less at right angles to the subtending hyphae, mid yellowish-brown or somewhat darker than the subtending hyphae, unbranched, non-septate, smooth, 11−19 μm long, (4.5−)5−6.5 μm wide. Conidiogenous cells monoblastic, integrated, terminal, determinate. Conidia solitary, dry, acrogenous, medium brown, helicoid, filament (6.5−)7.5−9.5 μm wide, smooth, distinct multiseptate, slightly constricted at the septa, tightly coiled (7−)8(−9) times in a clockwise direction to form a subglobose or broadly elliptical body, (57−)66−78(−87.5) μm long, (44−)58−72.5(−77) μm wide, with a length to width ration of (0.9−)1.1(−1.3), usually incorporated with mucilaginous substances such that no gaps are visible between adjacent coils, non-hygroscopic; conidial secession schizolytic at the deliminating septum of the conidiogenous cell, giving rise to a short pedicel of (7−)8−12.5 long and 5−6.5 μm wide at the base.

Material examined: ─ TAIWAN, Chiayi County, Juchi Township, on decaying wood submerged in a freshwater stream, 5 Feb 2017, Chang-Hsin Kuo, NCYU-K 3-2 (holotype: TNM F31003, deposited at National Museum of Natural Science, Taichung, Taiwan). Ex-type culture BCRC FU 30843, Bioresearch Collection and Research Centre ( BCRC), Food Industry Research and Development Institute, Hsinchu, Taiwan. The rest of the single-spore isolates were kept at the Department of Plant Medicine, National Chiayi University ( NCYU), Taiwan. GenBank accession numbers for rDNA derived from the type: LC316606 ( ITS), LC316607 ( ITS), LC316608 ( ITS), LC316609 ( ITS), LC316610 ( LSU), LC316611 ( LSU), LC316612 ( LSU).

Cultural characteristics: ─ Conidia of H. subglobosum germinated in culture. Germination rate from single-spore isolation was 60%, but growth was extremely slow, with a growth rate of 0.2 mm per d. Colonies on PDA slants produced from single-spores reached 6 mm diam. in 5 wk at 20 °C. On PDA plates, colonies attained 1 cm diam. in 80 d at 20 °C. Mycelium from culture comprised ramifying hyphae which were hyaline to brown, septate, (2.6−)2.9(−3.2) μm wide. Chlamydospores were formed in culture, which were uscous, guttulate, globose, (7.1−)9.1(−10.7) diam. ( FIG. 3 ).

Note: ─ Helicoön subglobosum is most similar to H. gigantisporum ( Goh & Hyde 1996b) based on phylogenetic analysis ( FIG. 5 , 6 ) and morphological comparison. Both species have large fuscous conidia producing from short conidiophores which arise as lateral branches from repent hyphae. They both occur on submerged wood from freshwater environments. The conidial filaments in both species are of comparable width, and coiled in a clockwise direction (in the sense of Glen-Bott, 1955). However, they differ in several ways and are distinct species. The conidia in H. subglobosum are subglobose (i.e. having a mean length to width ratio 1.1), whereas in H. gigantisporum they are doliiform (i.e. having a mean length to width ratio 1.5). Conidia are much larger in H. gigantisporum (78−123 μm long and up to 100 μm wide), whereas conidia are 57−78 × 58−72.5 μm in H. subglobosum . The similarities and differences between these two species are summarised in Table 3.

H. subglobosum H. gigantisporum

Conidiophores

Length 11−19 μm 6.5−14 μm

Width (4.5−)5−6.5 μm 3−4.5 μm

Conidia

Colour Medium brown Yellowish brown

Shape of body Subglobose Broadly ellipsoidal

Length of body (57−)66−78 μm 78−123 μm

Width of body 58−72.5 μm (48−)56.7−90(−100) μm

Length/width ratio (0.9−)1.1(−1.3) (1.4-)1.5(-1.7)

Length of pedicel (7−)8−12.5 μm 4−9 μm

Width of filament (6.5−)7.5−9.5 μm 6.5−10 μm

Number of coils (7−)8(−9) (12−)13

Direction of coiling Clockwise Clockwise

Constriction at septa Slighted constricted Slighted constricted

Wall texture Smooth Smooth

Habitat On wood submerged in freshwater On wood submerged in freshwater Known districbution Taiwan Australia, Thailand

Teleomorph Unknown Unknown

Phylogenetic placement Tubeufiaceae Tubeufiaceae

Including H. subglosum , there are now 18 species accepted in the genus Helicoön . A morphological comparison of these species was given in Table 4. A key to the genus is as follows.

Figures

FIGURE 1. Helicoön subglobosum (TNM F31003, holotype). a Colonies on natural substratum. b Group of conidia at low magnification; note the shapeof conidia is generally subglobose.c−e Highermagnification of conidia.f.A conidiumstill attaching to the short conidiophore arising from superficial hypha. Scale bars: a = 200 μm, b = 100 μm, c−d = 50 μm, e−f = 20 μm.

FIGURE 2. Helicoön subglobosum (TNM F31003, holotype). a−p Conidia showing a range of shapes, but mostly subglobose. Scale bars = 20 μm.

FIGURE 3. Helicoön subglobosum (BCRC FU30843, ex-type culture). a Single-spore colonies on PDA slants 5 weeks after incubation at 20C. b Colony on PDA plate 5 weeks after incubation at 20 °C. c Higher magnification of colony on PDA. d−e Chlamydospores in culture. Scale bars: a−b = 1 cm, c = 200 μm, d−e = 10 μm.

FIGURE 4. Helicoön subglobosum (TNM F31003, holotype). Scanning electron micrographs. a Colony on natural substratum. b−d Conidia and conidiophores on natural substratum. e Higher magnification showing the base of a conidium attaching to conidiophore arising from superficial hypha. f Higher magnification showing the base of a conidium which has detached from the conidiophore. Note that conidial secession is schizolytic. Scale bars: a = 50 μm, b−d = 20 μm, e = 10 μm, f = 5 μm.

FIGURE 5. Phylogenetic tree (TreeBase TB2:S21492) inferred from aligned ITS sequences of 45 taxa showing relationships of Helicoon species and representative taxa from various ordinal lineages using neighbor-joining method. The optimal tree with the sum of branch length = 2.14463852 is shown. Branch support values bootstrap tests (1000 replicates) above 50 are shown near the nodes (MEGA7/ RAxML/PhyML). The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The tree was rooted with Xylaria mellissii.

FIGURE 6. Phylogenetic tree (TreeBase TB2:S21492) inferred from aligned partial LSU sequences of 58 taxa showing relationships of Helicoon species and representative taxa from various ordinal lineages using neighbor-joining method. The optimal tree with the sum of branch length = 1.89900892 is shown. Branch support values bootstrap tests (1000 replicates) above 50 are shown near the nodes (MEGA7/RAxML/PhyML). The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The tree was rooted with Xylaria mellissii.