UV irradiation alters the levels of flavonoids involved in the defence mechanism of Citrus aurantium fruits against Penicillium digitatum

The effect of UV irradiation on the levels of the flavanone, naringin, and the polymethoxyflavone, tangeretin, in the peel of Citrus aurantium fruits is described, as changes in the synthesis and/or accumulation of these comp ounds after infection with Penicillium digitatum. The growth of P. digitatu m on previously irradiated fruit was reduced by up to 45%. Changes in flavo noid levels were detected, associated with inhibition of fungus growth, the naringin content falling by 69% and tangeretin levels increasing by 70%. T he possible participation of naringin and tangeretin in the defence mechani sm of this Citrus species is discussed.