Fruit colour responses of 'Granny Smith' apple to variable light environments

Fifteen sequences of sunlight exposure and exclusion were imposed on fruit of 'Granny Smith' apple (Malus domestica Borkh.) by covering individual fruit with opaque paper bags. Fruit were harvested at commercial maturity and fruit background colour, blush, soluble solids concentration, flesh firmness, and starch pattern index were measured. The following year, seven of the same sequences were repeated and fruit colour was measured at 10-day intervals beginning from fruit drop until commercial harvest. A strong linear relationship between fruit colour lightness and hue (visually perceived colour) was evident in both years. Fruit became lighter as greenness decreased while an increasing yellowness only slightly increased lightness. Longer durations of light exclusion resulted in lighter coloured fruit, but for a given duration of shading, fruit exposed 1 month before harvest were lighter than fruit which remained shaded until harvest. All fruit became lighter in colour with time, although the rate at which fruit became paler was increased by profound shading. The incidence and severity of blush was highest on fruit from which light had been excluded for more than 2 months and then re-exposed 1 to 2 months before harvest. Exclusion of light depressed the soluble solids concentration slightly, although flesh firmness and starch index were unaffected.