Fungal melanin could adapt tolerance to UV-C light

UV-C light (200-280nm) can combat a variety of microorganisms, including necrotrophic fungi like Botrytis cinerea (grey
mould), offering a viable alternative to agrochemical control. Yet a balance must be struck between controlling infection
and causing damage to plants. We exposed B. cinerea conidia and early vegetative mycelia to increasing UV-C doses (up
to 8 minutes), logging survival data, and colony-forming units. We then applied a non-toxic UV-C treatment (4 minutes)
with incubation at 4°C (postharvest conditions) and 21°C (production conditions). We then analysed changes in gene
expression in the melanin biosynthetic pathway. Initial survival trials confirm significant lethality in conidia with increasing UV-C
dose, but that mycelial-stage B. cinerea not only demonstrated lower lethality rates but also a darker phenotype
compared to untreated. Adaptive melanisation to non-lethal UV-C treatment highlights the need for a more comprehensive understanding of grey mould pathogenic biology under current commercial UV-C treatment.