Use of (pulsed) UV-C light to control spore germination and mycelial growth of storage diseases causing fungi, and effect on control of storage rot in apples and pears

A heavy reliance on synthetic fungicides has been necessary to control postharvest decay of fruits. Recently, there is an ongoing concern about pesticide residues on fruits. Consumers increasingly prefer fruits without pesticides, and this is used by supermarkets as a selling strategy (residue free fruit). The use of ultraviolet-C (UV-C, 190-280 nm wavelengths) offers interesting possibilities for controlling storage decay. UV-C acts directly by damaging the microorganisms on the exposed surfaces, and indirectly by stimulating defense mechanisms in the treated product. In our study the effect of UV-C on spore germination (inactivation) and mycelial growth was examined. All conidia of the tested fungal species were completely or partially killed with UV-C. However, conidia with dark pigments, such as Alternaria alternata and Venturia inequalis, were shown to be more resistant as compared with weakly pigmented conidia, such as Penicillium expansum and Botrytis cinerea. UV-C irradiation was not able to inhibit in vitro mycelial growth. However, a reduction in growth and sporulation was noticed for most tested fungal species. Intense light pulses (ILP) is a technique to decontaminate surfaces by killing micro-organisms using short time pulses of an intense broad light spectrum, including UV-C light. In a series of trials, the effects of ILP in controlling fruit rot caused by P. expansum and B. cinerea on apples (‘Elstar’) and pears (‘Conference’) was tested. It appeared that controlling fruit rot of these (inoculated) apples and pears was very difficult. Most likely due to UV-C shielding effects, which prevent the light beams from reaching the target