Production of phytoalexin, scoparone in citrus cultivars following treatment with UV radiation

Ultraviolet (UV) radiation induced production of phytoalexin scoparone (6, 7-dimethoxycoumarin) in the leaves and flavedo of various citrus cultivars. Using high performance liquid chromatography (HPLC) measured scoparone in the citrus leaves and fruits after radiated with UV. The amounts of scoparone in young leaves and fruits (harvested in August) were less than those in mature specimens (harvested in December). Among the cuitivars, abundant scoparone was induced in young leaves of lemon (Citrus limon (L.) Burm. f.), Meiwa kumquat (Fortunella crassifolia Swingle) and Ponkan (C. reticulata Blanco). Matured leaves of lemon, Hyuganatsu (C tamurana hort. ex Tanaka) and 'Seminole' tangelo also produced abundant scoparone. In August, Meiwa kumquat and lemon, and in December, Meiwa kumquat, 'Tsunokaori' and 'Robinson' fruits were induced to produce abundant scoparone by UV radiation. Duration of changes in scoparone synthesis differed among citrus cuitivars, organs and growth phases.