Yield comparison of hybrid Agaricus mushroom strains as a measure of resistance to Trichoderma green mold

Commercially available strains of hybrid white, hybrid off-white, and brown Agaricus bisporus mushrooms were compared for resistance to green mold cau sed by Trichoderma harzianum biotype 4 (Th4). Seven mushroom spawn strains were assessed for total weight of mushrooms (grams per 0.1 m(2)) with or wi thout the addition of an aqueous Th4 spore suspension added at spawning tim e. Cropping studies were conducted at the Mushroom Research Center (Pennsyl vania State University) to emulate commercial growing operations. Excessive spawn handling had no significant effect on development of green mold. Sev erity of green mold was related to time between infestation and green mold appearance, with more significant yield losses occurring when green sporula tion was detected early in production. Significant differences in yield wer e measured among mushroom strains in response to Th4 infestation. Hybrid wh ite strains were extremely susceptible, with a mean yield loss of 96%. Hybr id off-white strains exhibited intermediate susceptibility, with mean yield losses of 56 to 73%. Brown strains were highly resistant, with mean yield losses of 9 to 16%. From these findings, we report the existence of green m old resistance, with a continuum of resistance among spawn strains. The fin dings suggest use of brown strains to manage green mold outbreaks, particul arly where benomyl resistance in Trichoderma spp. is a threat.