Pythium cedri Jia J. Chen & X.B. Zheng, 2017

Chen, Jia-Jia, Lü, Li, Ye, Wen-Wu, Wang, Yuan-Chao & Zheng, Xiao-Bo, 2017, Pythium cedri sp. nov. (Pythiaceae, Pythiales) from southern China based on morphological and molecular characters, Phytotaxa 309 (2), pp. 135-142 : 137-140

Pythium cedri Jia J. Chen & X.B. Zheng , sp. nov. ( Figs. 2–3 )

MycoBank no.: MB 818071

Differs from other Pythium species by presence of hyphal swellings, toruloid sporangia, ornamented oogonia with blunt spines, monoclinous antheridia, plerotic or nearly plerotic oospores, and relatively slow growth (11–15 mm d –1).

Type.— CHINA. Jiangsu Prov.: Nanjing, Qianhu Park, alt. 158 m, on roots of Cedrus deodara , 14 September 2015, Chen 4 (holotype, NJAU).

Etymology.— Cedri (Lat.) referring to the host from which it was isolated.

Colonies submerged, with stellate pattern on CMA, rosette pattern on PCA, and stellate pattern on 10% V8 juice agar (V8A). Average growth rates 3 mm day−1 at 10°C, 4.5 mm day−1 at 15°C, 7 mm day−1 at 20°C, 11 mm day−1 at 25°C, 14.8 mm day−1 at 30°C, 4.5 mm day−1 at 35°C, but when returned to room temperature both of them started to grow again. Cardinal temperatures: minimum 5°C, optimum 30°C, maximum 37°C. Main hyphae hyaline, aseptate, up to 4.0 μm wide ( Fig. 3A ).

Hyphal swellings terminal or intercalary, globose or subglobose, 8.0–15.0 μm (mean 12.4 μm) in diameter ( Fig. 3B ). Zoospores not formed. Sporangia spherical, toruloid or rarely irregular ( Fig. 3C–I ), terminal or intercalary, 10–25 (mean 15) μm in diameter in spherical sporangia, 50–150 × 17.5–25 (mean 88.5 × 21.5) μm in other shaped sporangia. Oogonia globose, terminal, ornamented with blunt spines, 17.5–32.5 μm (mean 24.1 μm) in diameter. Spines 2.5–4 μm long and 1–2.4 μm in diameter at the base. Antheridia monoclinous, one to three per oogonium ( Fig. 3J–O ); antheridial stalks unbranched; antheridial cells subclavate to subcircular or slightly elongated along the oogonial stalk, 5.7–12.0 × 3.5–12.5 μm (mean 7.5–8.6 mm). Oospores plerotic or nearly plerotic, globose, 14.3–26.5 μm (mean 21.3 μm) in diameter, hyaline ( Fig. 3J–O ). Oospore wall 0.4–1.3 μm (mean 0.6 μm) thick.

Additional specimens examined. — CHINA. Jiangsu Prov.: Nanjing, Qianhu Park, alt. 158 m, on roots of Cedrus deodara , 13 April 2016, Chen 28–30 (paratypes, NJAU).

Figures

FIGURE 2. Cedrus deodara infected with Pythium cedri. A. Dieback of crowns. B–C. Rotten roots.

FIGURE 3. Asexual and sexual reproductive bodies of Pythium cedri (Chen 4). A. Mycelium. B. Hyphal swellings. C. Various sporangia. D. Globose and toruloid sporangia. E. Intercalary sporangium. F–H. Toruloid sporangia. I. Terminal sporangium. J. A terminal oogonium with a nearly plerotic oospore and a monoclinous antheridium. K. Plerotic oospore and round antheridial cell. L. Elongated antheridial cell wavy in contour. M. Plerotic oospore and two antheridia. N. Clustering of several antheridial cells around the oogonium. O. A terminal oogonium with a nearly plerotic oospore and a monoclinous antheridium. Scale bars A–I=10 μm, J–O=20μm.