Trichoderma species associated with the green mold epidemic of commercially grown Agaricus bisporus

Abstract

Trichoderma aggressivum sp. nov. and T. aggressivum f. europaeum f. nov. are described. These forms cause the green mold epidemic in commercially grown Agaricus bisporus in North America and Europe, respectively. In the literature they have been reported as T. harzianum biotypes Th 4 and Th 2, respectively. They are strongly separated from their closest relative, T. harzianum, in sequences of the ITS-1 region of nuclear rDNA and an approximately 689 bp fragment of the protein coding translation elongation factor gene (EF-1α). They are distinguished from the morphologically similar T. harzianum and T. atroviride (the latter also known as biotype Th 3) most readily by rate of growth. Of these, only T. harzianum grows well and sporulates at 35 C, while T. atroviride is the slowest growing. Trichoderma aggressivum f. aggressivum and f. europaeum are effectively indistinguishable morphologically although they have subtly different growth rates at 25 C on SNA and statistically significant micromorphological differences. Based on findings of this study, descriptions of T. harzianum and T. atroviride are expanded. A key to Trichoderma species commonly found associated with commercially grown A. bisporus is provided.

• green mold disease
• Hypocrea
• Hypocreales
• ITS
• systematics
• translation elongation factor 1 alpha gene (EF-1α)
• Trichoderma aggressivum
• Trichoderma atroviride
• Trichoderma harzianum

Several people provided us with strains used in this study, including Drs. J. Bissett, L. Gullino, G. Harman, P. Hebbar, R. L. Lumsden, Weili Mao, S. Muthumeenakshi, T. Okuda, C. P. Romaine, D. Royse and P. Tondjé. We are especially grateful to Drs. C. P. Romaine and Xi Chen for confirming the identity of many strains and for giving us access to unpublished data. Dr. C. P. Kubicek kindly provided us with elongation factor primers. Drs. P. Crous, D. Geiser and A. Rossman made suggestions that substantially improved the text. Technical assistance was provided by Mr. N. Parique and Ms. P. Mathur. Mr. J. Plaskowitz prepared the illustrations. The research was supported in part by the U.S. National Science Foundation ‘PEET’ grant to the Dept. of Plant Pathology, The Pennsylvania State University (Monographic Studies of Hypocrealean Fungi: Hypocrea and Hypomyces DEB-9712308).