The Two Mycological Sides of Ultraviolet-B Radiation: Harmless for Mushroom Mycelia, Harmful for Mycopathogenic Mould Spores

Mycopathogenic moulds are responsible for the greatest crop losses of cultivated mushrooms, thus having a significant negative economic impact on industry. Pesticides are the most common treatment against mycopathogenic moulds, but ultraviolet-B (UV-B, 280-315 nm) radiation could be a more ecological alternative. Thus, we studied the effect of UV-B (at doses from 8 to 192 kJ m-2) on four common mycopathogenic moulds (Cladobotryum mycophilum, Lecanicillium fungicola, Trichoderma aggressivum, and Mycogone perniciosa) under in vitro conditions, using four different culture media. UV-B was tremendously effective in inactivating mould spores even at the lowest dose, with the exception of those of T. aggresivum. Contrarily, UV-B did not present any effect on the development of the host mycelium (Agaricus bisporus), even at the highest dose, when cultivated on Compost Tea medium (CT). This is the most similar medium to the substrate used for commercial mushroom cultivation. UV-B reduced the mould mycelia development in a dose-response manner, but this reduction depended on the species, with the strongly pigmented T. aggressivum as the most tolerant species. Regarding the culture media, all of them (especially CT) absorbed UV-B intensely, contributing to the protection of the mycelia. Overall, UV-B radiation could constitute an ecologically friendly alternative to chemical treatments against mycopathogenic moulds, due to its capacity to inactivate their spores and (in some cases) their mycelia without affecting their hosts.