Isthmomyces macrosporus Z. F. Yu, M. Qiao & R. F. Castaneda, 2021

Qiao, Min, Zheng, Hua, Guo, Ji-Shu, Castaneda-Ruiz, Rafael F., Xu, Jian-Ping, Peng, Jie, Zhang, Ke-Qin & Yu, Ze-Fen, 2021, Two new asexual genera and six new asexual species in the family Microthyriaceae (Dothideomycetes, Ascomycota) from China, MycoKeys 85, pp. 1-30 : 1

Isthmomyces macrosporus Z. F. Yu, M. Qiao & R. F. Castaneda sp. nov.

Figs 5 , 9d

Etymology.

Greek, macrosporus, referring to the large, great conidia.

Description.

Asexual morph hyphomycetous. Colonies on PDA amber to fawn, reverse fawn, attaining 2 cm diam. after 20 days at 25 °C. Mycelium mostly immersed, composed of branched, septate, slender, colourless hyphae. Conidiophores macronematous, mononematous, cylindrical, erect, straight, unbranched, 0-1-septate, smooth, pale brown, 25-35 × 3.0-3.5 µm. Conidiogenous cells polyblastic, cylindrical, denticulate, sympodial extended, integrated, terminal, pale brown or subhyaline. Conidia acrogenous, isthmospore, long fusiform, hyaline, smooth, 36.5-73.0 µm long, strongly constricted at the conspicuous, narrow, tiny central isthmus, sometime not differentiated, composed of two cellular isthmic-segments: i) basal isthmic-segment clavate, truncated at the base, 1-septate, hyaline or subhyaline, smooth, 19.2-31.1 × 4.5-6.7 µm; ii) apical isthmic-segment 0-1-septate, narrow obclavate, sometimes sub-obspathulate, rounded at the tip, unicellular, guttulate, hyaline or subhyaline, smooth, 21.1-42.0 × 3.3-5.4 µm. Sexual state: unknown.

Type.

China, Hainan Province, Limu Mountain National Conservation Area, on submerged leaves, April 2015, J. Peng. Holotype YMF 1.04518, preserved in a metabolically-inactive state (deep freezing) in the Conservation and Utilization of Bio-Resources in Yunnan. Ex-type culture CGMCC 3.18824.

Notes.

Phylogenetically, Isthmomyces macrosporus is close to I. dissimilis and I. lanceatus . However, I. macrosporus is different from all species within this genus by having larger conidia, obviously brown conidiophores and few denticulate conidiogenous cells (Hoog and Hennebert 1983).

Figures

Figure 5. Isthmomyces macroporus (Holotype YMF 1.04518) a conidia b conidiophore with conidia under low objective c conidiophore and conidiogenous cell d conidiophore and developing conidia. Scale bars: 10 µm (a, c, d); 50 µm (b).

Figure 9. Cultural characters of all species in this study after 20 days on PDA at 25 ° C.