Morphological and molecular identification of Trichoderma isolates on North American mushroom farms

Abstract

Green mold disease (causal agent, Trichoderma) has resulted in severe crop losses on mushroom farms worldwide in recent years. We analyzed 160 isolates of Trichoderma from mushroom farms for morphological, cultural, and molecular characteristics and classified these isolates into phenotypic groups. The most common group comprised approximately 40% of the isolates and was identified as a strain of Trichoderma harzianum. This group was consistently recovered from farms with severe green mold disease but not from farms with little or no problem. In addition, the strain identified as the major cause of green mold disease in Ireland and the United Kingdom grouped with these North American isolates in having very similar randomly amplified polymorphic DNA patterns.

FIG. 1

Amplification of the ITS region of Trichoderma isolates. DNA sequences flanked by ITS1 and ITS4 primers were amplified by PCR. The products were digested with BamHI, and the fragments were separated by agarose gel electrophoresis. Lane M contains a 100-bp size standard (Pharmacia). Results characteristic of phenotype 1 are observed in lanes 1 (BamHI-digested amplification product) and 2 (undigested). Lanes 3 (digested) and 4 (undigested) show phenotype 2, due to the presence of a single restriction site which resulted in 560- and 140-bp digestion products. Phenotype 3 is seen in lanes 5 (digested) and 6 (undigested). Two fragments, 480 and 220 bp in length, were produced by BamHI digestion. Lane C contains products from a water control reaction in which a DNA template was omitted.