MycoBank no.: MB816874

Etymology. olgensis refers to the host tree, Larix olgensis.

Perithecium base globose, smooth, black, (64–)65–110(–152) μm in diameter (mean = 88.5 μm), ending in a dark brown to black, smooth perithecial neck, (40–) 43–70(–99) μm long (mean = 56.7 μm), (14–)19–36(–38) μm wide at the base (mean = 24.99 μm), (5–)5–11(–22.5) μm wide at the apex (mean = 7.5 μm), with apical ostiolar hyphae (6–)7.5–39(–42) μm long (mean = 24.1 μm); asci evanescent; ascospores reniform in side view, hyaline, aseptate, without mucilaginous sheath, (2–)3.5–4.5(–6) μm × (0.5–)1–1.5(–2) μm.

Asexual form Hyalorhinocladiella -like and abundant, between perithecia, forming white fluffy masses; conidiophores of variable length, (3–)6.5–55.5(–100) μm long (mean = 20.7 μm) × (1–)1.5–4(–5.5) μm wide; conidia hyaline, aseptate, obovoid with pointed bases and rounded apices (1–)1.5–6(–8.5) μm × (1–)1.5–4(–6.3) μm.

The optimal temperature for growth of the strains was 30 °C, with little growth observed at 5 °C and 35 °C. Strains grown at 30 °C 14 mm /day, much faster than growth at 25 °C, which was 11 mm /day.

Holotype:— CHINA, Heilongjiang: from Ips subelongatus infecting Larix olgensis, August 2011, collected by Q. Lu, ex-holotype culture CXY 1410.

Additional specimens examined:— CHINA, Heilongjiang: from I. subelongatus infecting L. olgensis, August 2011, collected by Q. Lu (CXY 1411); Inner Mongolia autonomous region: from I. subelongatus infecting L. gmelini, July 2012, collected by Q. Lu & X. J. Meng (CXY 1404, CXY 1405, CXY 1406, and CXY 1408).

Known hosts and substrate: — Larix gmelini and L. olgensis, galleries of I. subelongatus.

Known insect vector:— Ips subelongatus.

Known distribution:— China.

Pathogenicity tests

Ten weeks after inoculation, none of the trees had visible disease symptoms from the viewpoint of the crown. After removal of the outer bark, no lesions were produced in the control treatments. Both O. olgensis (strains CXY 1406, CXY 1410) and O. kryptum (strains DAOM 229701) produced obvious lesions (Table 3). O. olgensis and O. kryptum were easily re-isolated from selected lesions; no Ophiostoma fungus was isolated from the controls.