Pythium subinflatum Jia J. Chen & X.B. Zheng, 2020

Chen, Jia-Jia, Feng, Hui, Song, Wei & Zheng, Xiao-Bo, 2020, Two new Pythium species from southern China based on morphological and molecular characters, Phytotaxa 432 (3), pp. 263-273 : 266-268

Pythium subinflatum Jia J. Chen & X.B. Zheng , sp. nov. ( Fig. 2 )

MycoBank no.: MB 822956

Differs from other Pythium species by globose to sub-globose or ovoid hyphal swellings, filamentous inflated sporangia, smooth oogonia, mostly diclinous antheridia, elongated along the oogonial stalk, subcircular, subglobose or fist-shaped antheridial cells, and aplerotic and slightly thick-walled oospores (2–3.5 µm).

Type.— CHINA. Jiangsu Prov.: Xuzhou, 117.05°E, 33.38°N, on roots of Glycine max , April 2016, Chen 262 (holotype, NJAU).

Etymology.— Subinflatum (Lat.): referring to the species is somewhat similar to Pythium inflatum .

Colonies submerged, with radiate pattern on CMA, radiate pattern on PCA, and radiate pattern on 10% V8 juice agar (V8A). Average growth rates 6 mm day−1 at 10°C, 8 mm day−1 at 15°C, 15 mm day−1 at 20°C, 20 mm day−1 at 25°C, 27 mm day−1 at 30°C, 15 mm day−1 at 35°C. Cardinal temperatures: minimum 5°C, optimum 30°C, maximum 38°C. Main hyphae hyaline, aseptate, up to 5.0 µm wide. Hyphal swellings globose to sub-globose or ovoid, terminal, intercalary or catenulate, 8.5–25 (mean 18.5) μm in diameter ( Fig. 2A–C ). Sporangia filamentous inflated, consisting of lobate elements ( Fig. 2D–E ). Homothallic; oogonia globose, smooth, terminal, 23–30 µm (mean 26 µm) in diameter. Antheridia mostly diclinous, sometimes monoclinous, one to two per oogonium ( Fig. 2F–L ); antheridial stalks unbranched; antheridial cells elongated along the oogonial stalk, subcircular, subglobose or fist-shaped. Oospores aplerotic, globose, 20–25 μm (mean 23 µm) in diameter, hyaline. Oospore wall 2–3.5 µm (mean 2.5 µm) thick.

Additional specimens examined. — CHINA. Shandong Prov.: Jining, 116.35°E, 35.27°N, on roots of Glycine max , April 2016, Chen 263 (paratypes, NJAU).

Remarks.— Pythium subinflatum is characterized by globose to sub-globose or ovoid hyphal swellings, filamentous inflated sporangia, smooth oogonia, mostly diclinous antheridia, elongated along the oogonial stalk, subcircular, subglobose or fist-shaped antheridial cells, and aplerotic and slightly thick-walled oospores (2–3.5 µm). Phylogenetically P. subinflatum belongs to Pythium subclade B1d in the phylogenetic tree and is closely related to P. inflatum V.D. Matthews according to the ITS and COI-based phylogeny with low support (73% MP and 0.59 BPPs; Fig. 1 ). The species in subclade B1d are characterized by filamentous inflated sporangia and relatively high cardinal temperatures for growth (optimum 30°C, maximum 40° C, Lévesque & de Cock 2004). P. subinflatum shares the above characteristics with other Pythium subclade B1d species, however, P. subinflatum can be readily distinguished in having fast growth rate (20 mm d –1). P. inflatum resembles P. subinflatum in having filamentous inflated sporangia, but it is distinguished in its smaller oogonia (20–24µm), plerotic or nearly plerotic oospores, and slower growth (10 mm d –1, Table 3, van der Plaats-Niterink 1981).

Figures

FIGURE 1. Phylogeny of species in Pythium clade B species generated by maximum parsimony based on ITS+COI sequences. Branches are labeled with parsimony bootstrap proportions (before slanting line) high than 50% and Bayesian posterior probabilities (after slanting line) more than 0.95.

FIGURE 2. Asexual and sexual reproductive bodies of Pythium subinflatum (Chen 262).A. Catenulate hyphal swellings. B–C. Globose, terminal hyphal swellings. D–E. Filamentous, inflated sporangia. F–H. Globose, smooth and terminal oogonia. I. Oogonium with a projection. J. Aplerotic oospore. K. Diclinous antheridium. L. Aplerotic oospore and two antheridia. Scale bars A =2 μm, B–J=10 μm.