Pathogen Growth Inhibition in Ocimum Basilicum (L.), Malus Domestica (Borkh.), and Citrus Limon (L.) by Low-Dose UV-C LED Exposure

Abstract

In order to stimulate hormesis in basil, apple and lemon we used Ultraviolet C-band (UV-C) radiation emitted by an array of Light-Emitting Diodes (LEDs) at low irradiation doses followed by inoculation of the pathogens Botrytis cinerea and Penicillium digitatum. The LEDs are preferable to conventional mercury lamps when robustness and portability are required. Hormetic doses lower than those reported in the literature were used, in order to achieve short irradiation times and thus rapid treatment of crops. The results show that a dose of just 0.3 kJ m-2 released in a time interval of 3 to 14 seconds generates metabolites that inhibit, or dramatically slow, pathogen growth. After 75 days from irradiation immediately followed by inoculation, the fungal development on basil plants affected less than 30% of the epigeal part, compared to 90% in the unirradiated control. In addition, we obtained preliminary results of low-dose hormetic irradiation of lemons and apples. No fungal growth was observed in 75% of irradiated apples 15 days after irradiation and inoculation. Irradiated lemons showed complete inhibition of P. Digitatum growth. One can then infer that preventive irradiation by LED is beneficial to limit crop diseases in both pre-harvest and post-harvest without harming the plant or the environment, as a sustainable alternative to pesticides.