Colour differentiation of high-lycopene tomato fruit through the addition of the colourless-epidermis (y) mutation

Abstract

High-lycopene tomatoes (Solanum lycopersicum) are characterised by an intense red flesh-colour, due to an elevated concentration of the carotenoid, lycopene. However, this characteristic is only visible once fruit are cut open, making it impossible to differentiate intact high-lycopene fruit from standard tomato fruit, a clear market disadvantage. The reason that fruit colour of both high-lycopene and standard fruit looks almost identical from the outside is because tomato fruit normally contain the yellow flavonoid 'naringenin chalcone' in a thin layer of epidermal cells. It is this combination of naringenin chalcone and the underlying lycopene in the flesh that gives tomatoes their characteristic orange-red colour. By incorporation of the recessive colourless epidermis mutant allele 'y' (which prevents naringenin chalcone accumulation) into high-lycopene fruit, we have been able to create high-lycopene tomatoes (hp1.ogc.y) exhibiting a deep-pink colour visible from the outside. Hue angle of the skin of the high-lycopene 'y' mutant and a regular highlycopene tomato (hp1.ogc.Y) was 30 and 38°, respectively, while flesh values were similar at 31 and 32°, respectively. Removal of naringenin chalcone from the epidermis appeared to improve the visibility of underlying lycopene, such that fruit outer colour became a subsequent indicator of underlying flesh colour. The removal of epidermal pigmentation means that high-lycopene fruit can now be differentiated from standard tomato fruit in the market place without the need to cut fruit open.