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

Figs 6 , 9e

Etymology.

Greek, oxys, meaning sharp, keen, sporum, referring to the conidia.

Description.

Asexual morph hyphomycetous. Colonies on CMA pale mouse grey to dark mouse grey, reverse olivaceous-grey, attaining about 2 cm diam. after 20 days at 25 °C. Mycelium mostly immersed, composed of branched, septate, subhyaline to hyaline hyphae. Conidiophores macronematous, mononematous, cylindrical, erect, smooth, 0-1-septate, subhyaline to hyaline, mostly reduced to conidiogenous cells, up to 30 µm long, 2.5-3 µm wide, arising from the creeping hyphae. Conidiogenous cells polyblastic, cylindrical, denticulate, integrated, terminal, sympodial extended, hyaline. Conidia isthmospore, fusiform, hyaline, smooth, 20.5-25.5 µm long, strongly constricted at the narrow, tiny central isthmus, composed of two cellular isthmic-segments: i) basal isthmic-segment broadly clavate to clavate, unicellular, hyaline 9.7-13 × 2.0-4.0 µm; ii) apical isthmic-segment narrow obclavate to obclavate, obpyriform or rarely lecythiform, unicellular, hyaline, 9.0-13.0 × 2.0-3.0 µm. Sexual state: unknown.

Type.

China, Hainan Province, Diaoluo Mountain Natural Reserve, on submerged leaves, August 2015, J. Peng. Holotype YMF 1.04513, preserved in a metabolically-inactive state (deep freezing) in the Conservation and Utilization of Bio-Resources in Yunnan. Ex-type culture CGMCC 3.18821.

Notes.

Morphologically, Isthmomyces oxysporus resembles Isthmolongispora asymmetrica Aramb. & Cabello in having both tapering isthmic-segment ends, but Is. asymmetrica has asymmetrical conidia, in which the basal isthmic-segment is longer (17-20 µm long) ( Arambarri et al. 1987). Besides, I. oxysporusis is somewhat similar to Is. rotundata Matsush. in conidial sizes, but the apical isthmic-segments in Is. rotundatus are rounded at the tip ( Matsushima 1987).

Figures

Figure 6. Isthmomyces oxysporus (Holotype YMF 1.04513) a conidia b conidiophores and conidiogenous cells. Scale bars: 10 µm (a, b).

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