On the other hand, the selected UV-C and UV-B radiations could reduce the oxygenated monoterpenes under 17% and enhance the hydrocarbon monoterpene production up to 42% (6 h UV-C and UV-B WG 305 exposures) in the irradiated DO callus (Fig. 4). The RR control callus showed a completely different trend in the monoterpene production as its aroma was originally characterised by higher levels of hydrocarbon monoterpenes (38%) than oxygenated ones (22%). Therefore, the effect of some UV irradiations seemed to balance these two terpene classes in the DO callus aroma to the levels found for the RR basil callus (Fig. 4).