Etiology and epidemiology of Trichoderma harzianum rifai in association with the cultivated mushroom Agaricus bisporus (Lange) imbach

The objective of these studies was to examine etiological and epidemiological factors that contribute to the development of Trichoderma green mold in A. bisporus mushroom production. With the loss of Benlate (benomyl, E. I. DuPont, Wilmington, DE), this information may be used to enhance disease management of green mold on mushroom farms.; Commercially available A. bisporus mushroom strains with varying levels of pigmentation exhibited differential susceptibility to green mold. A hybrid white strain sustained mean yield losses of 96%, hybrid off-white strains exhibited intermediate resistance with yield losses ranging from 56–73%, and brown strains displayed yield losses of 8–14%.; SEM analysis showed that where Th4 spores were visible in association with A. bisporus, there was a reduced incidence of calcium oxalate crystals along the A. bisporus hyphae. On healthy brown mushroom mycelia, short crystals appeared to coat the surface of A. bisporus with greater density than other strains. Crystal length was measured, and the brown strain had significantly (p < 0.05) shorter crystals (3.6 μm) than crystals on both hybrid white (4.8 μm) and hybrid off-white (8.0 μm) mushroom strains. SEM analysis showed no evidence that Th4 directly parasitized A. bisporus through hyphal interactions.; When calcium oxalate was added to media, Th4 sporulation was reduced at levels of 600, 800, and 100 μg ml−1, suggesting that calcium oxalate crystals on A. bisporus may be limiting the growth of Th4. Cropping studies showed a significant reduction in yield loss when 100 g calcium oxalate was added to 500 g spawn. Although spawn amended with calcium oxalate was not completely protected from green mold, yield was improved at the 100 g level by approximately 50% (1327 g/0.1 m2) compared with the untreated control (655 g/0.1 m2). No significant yield gain was provided by other calcium or oxalate salts.; Several statements can be made with regard to the pathogenesis of Th4 in association with A. bisporus. First, mushroom strains are not equally susceptible to Th4. Second, Th4 does not appear to parasitize A. bisporus using direct hyphal interactions. Finally, calcium oxalate may have a role in the relationship between Th4 and A. bisporus.