Isolation of Trichoderma harzianum Th2 from Commercial Mushroom Compost in Spain

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Abstract
Trichoderma spp. are associated with green mold of mushrooms. This fungal disease has caused severe losses in mushroom production in countries such as Ireland, the United Kingdom, Canada, and the United States. This disease is caused by two biotypes of T. harzianum (Th2, Europe; Th4, North America) (1,2). Both biotypes have not been detected in mushrooms or other material in Spain previously. However, during 1998, green mold was detected at facilities dedicated to produce compost, as well as in facilities used to produce Agaricus bisporus (Lange) Imbach. Three compost samples were isolated from commercial bags with mushroom substrate and three more samples were taken from mushroom yards. Several spores were isolated by the dilution plate method. Initial identification of the pathogenic fungi was made by examining cultures grown on potato dextrose agar. Morphological characteristics of all isolates coincided with the description of T. harzianum (3). The following amounts of CFU per g were found in commercial compost samples: 1.2 × 108, 5.5 × 107, and 1.4 × 107 per g; whereas 3 × 108, 12.4 × 107, and 2.2 × 106 were obtained from mushroom yards. The fragment containing the internal transcribed spacer (ITS1) was amplified and sequenced for each of the six samples obtained. The ITS1 sequence (201 bp) was identical in all samples, and the sequence was aligned, with Clustal W, with Th2 and Th4 biotype sequences of the EMBL data base. The ITS1 sequence showed 0.55% divergence from Th2 isolates and more distance, 3.3%, with Th4 isolates. The ITS1 sequence obtained with all Spanish samples studied, EMBL accession number AJ1321550, was identical to that described for the Irish isolate Th2I (#63), with accession number U78880 in the EMBL data base (1). This is the first description of the Th2 biotype in Spain. References: (1) M. D. Ospina-Giraldo et al. Mycologia 90:76, 1998. (2) D. L. Rinker et al. Mushroom World 8:71, 1997. (3) D. A. Seaby. Plant Pathol. 45:905, 1996.

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