Members of the Phellinus weirii complex cause laminated root rot of living conifers. The cedar type (P. weirii (Murrill) Gilb. sensu stricto) of the complex is usually found on species of the Cupressaceae family, especially Thuja plicata in western North America, and the Douglas-fir type (P. sulphurascens Pilát) is found on species of the Pinaceae family (1,2,3). Outside North America, P. weirii occurs on species of Juniperus in the Ural Mountains, and P. sulphurascens occurs on other conifers in eastern Asia, including China (1). During a field inventory of wood-decay fungi in western China in 2003, laminated root rot of Sabina przewalskii (synonym Juniperus przewalskii) was found in natural forests of the Qilian Mountains in Qinghai Province (37°36′N and 102°15′E). Trees were approximately 80 to 150 years old and occurred in pure stands. Distinct disease patches that were as much as one hectare consisted of dead-standing and symptomatic trees, suggesting that the fungus spread by root contact. Symptomatic trees showed slow growth, thin crowns, and chlorotic foliage. After cutting several of the symptomatic trees, cambial necrosis and wood decay were found, and the trees apparently died when the cambial necrosis girdled the base of the trees. The wood of infected trees was reddish brown at the early stages of decay and later had numerous small cavities and separated into sheets at the junction of annual rings. Perennial, poroid, resupinate, dark brown basidiocarps formed on the root surface of dead trees. The basidiocarps had a monomitic hyphal system, hyphae without clamp connections, trama tissue with hyphoid setae, and thin-walled, hyaline, smooth, ellipsoid basidiospores. The fungus was identified as P. weirii and distinguished from P. sulphurascens by its perennial basidiocarps, smaller pores (5 to 8 versus 4 to 5 per mm), and narrower hyphoid setae (4 to 6 versus 5 to 10 μm in diameter). P. weirii also resembles P. ferrugineofuscus (P. Karst.) Bourdot in macro-morphology, but the latter species is a saprophyte and has allantoid to almost lunate basidiospores. The studied specimens of P. weirii and P. sulphurascens are preserved at the herbaria of the Botanical Museum of the University of Helsinki, the Institute of Applied Ecology, and the Chinese Academy of Sciences as DAOM 8734, Lowe 6960, TAA 52744, 55644, and 103812, and Dai 988, 2053, 2061, 2527, and 5067. To my knowledge, this is the first report of P. weirii sensu stricto from China and the first report of laminated root rot on S. przewalskii.
References: (1) Y. C. Dai and G. F. Qin. Fungal Sci. 13:101, 1998. (2) E. M. Hansen et al. Species limits for Phellinus weirii. Pages 119--127 in: Root and butt rots of forest tress. Int. Conf. Root and Butt Rots, INRA, France, 1998. (3) M. J. Larsen et al. Mycologia 86:121, 1994.