Fungus/Mushroom Resource and Research Center, Tottori University, Tottori 680-8553, Japan(Received on February 7, 2011; Revised on February 1, 2012; Accepted on February 15, 2012)During investigating of shiitake mushroom competitors,289 isolates of Trichoderma spp. were collected fromshiitake mushroom farms in different districts and theForest Mushroom Research Center of Korea, amongwhich 29 representative strains were selected. Based onthe DNA sequences of the rpb2 and tef1 genes and theITS rDNA, and their morphological characteristics,they were identified as T. atroviride, T. citrinoviride, T.harzianum, T. longibrachiatum, and two undescribedspecies, Trichoderma spp. 1 and 2, which are consideredto be the candidate of new species. Competition testsbetween Lentinula edodes (Sanjo302) and the Tricho-derma species indicated that the six species of Tricho-derma were significantly different from each other interms of their ability to invade the mycelial blocks ofshiitake. In both of dual cultures on potato dextroseagar and sawdust media, Trichoderma spp. 1 and 2strongly invaded the mycelial blocks of shiitake. Ourresults suggest that the two Trichoderma species maycause potentially serious economic losses in shiitakecultivation of Korea.Keywords : competition test, ITS, phylogenetic analysis,rpb2, tef1Shiitake mushrooms (Lentinula edodes) are widely culti-vated as a food source in East Asia and are dried andexported to many countries because of its special flavor andaroma (Chen, 2005; Luo, 2004). Recent research has indi-cated that the shiitake mushroom also has useful clinicaleffects, including an immunostimulant (Yamamoto et al.,1997). In Korea, the consumption of shiitake mushrooms isincreasing annually since 1999, and there are now about 20cultivars of shiitake, which were promoted and disseminat-ed by the Forest Mushroom Research Center.The genus Trichoderma is one of the most importantpathogens in the cultivation of the shiitake mushroom, andoften causes severe damage during its production (Miyazakiet al., 2009). Trichoderma species mainly attack the myceliaof L. edodes in bed logs and sawdust cultures. The identi-fication of Trichoderma at the species level has proveddifficult because of their interspecific morphological simi-larities (Chaverri and Samuels, 2003). It led to the establi-shment of “aggregate” species concept by Rifai (1969) thatall Trichoderma species could be distinguished to nineaggregates. Later, Bissett (1984, 1991a, b, c) established anew system of Trichoderma classification based on thebranching pattern of conidiophores and the characteristicsof phialides and conidia. After the introduction of mole-cular methods in Trichoderma taxonomy, the species con-cept of Trichoderma has changed dramatically (Chaverriand Samuels, 2003; Jaklitsch, 2009). In addition, the phylo-genetic data helped to establish the relationship betweenanamorph Trichoderma and their related teleomorph Hypocrea(Chaverri and Samuels, 2003; Samuels et al., 1998, 2002).In recent years, Park et al. (2005, 2006) identified sevendistinct species of Trichoderma from that Trichodermaisolates from green mold of oyster mushroom were identi-fied as seven distinct species (T. pleuroticola, T. pleurotum,T. atroviride, T. citrinoviride, T. harzianum, T. longibrachi-atum and T. virens). However, little is known about thespecies of Trichoderma associated with the green moldobserved on the shiitake mushrooms in Korea, and onlyfive species of Trichoderma (T. citrinoviride, T. harzianum,T. polysporum, T. longibrachiatum and T. viride) were