FIG. 4.

PCR analysis of 17 isolates of Trichoderma collected from mushroom cultures prior to the epidemic between the 1950s and 1990. Shown are the amplification products resolved by gel electrophoresis after RAPD-PCR with primer OPA13 (A) and PCR with the Th-F and Th-R primer set targeting a unique genomic sequence in biotypes 2 and 4 (B). Numbers above the lanes refer to the isolates by their PSU accession numbers. M, 100-bp DNA ladder. Isolates 14, 15, and 125 to 139 are preepidemic isolates. Isolate 72 is a positive control for the DNA template of biotype 4. N, negative control in which sterile water was substituted for the DNA template.