Fruit colour, leaf nitrogen level, and tree vigour in ‘Fuji’ apples

Abstract

A survey of red colour in ‘Fuji’ apple (Mains domestica Borkh. ) fruit from trees in orchards situated in three regions of New Zealand has confirmed that tree vigour, tree nitrogen (N) status, and region are important factors determining the extent and intensity of red colour development. The survey was conducted in Hawkes Bay and Nelson in 1990 and Hawkes Bay and Canterbury in 1991. In both years, a multiple regression model using leaf N concentration in February, tree vigour, and region as predictors for the intensity of red colour (chroma) gave the best fit to the data (r² = 0.65, 1990; r² = 0.46, 1991). Interaction terms for leaf N status and region, and growth rate and region were also significant. A multiple regression model over both years for Hawkes Bay found leaf N concentration in February and growth rate to be useful predictors for chroma (r² = 0.66). Leaf N status and tree vigour appear to act separately, and direct effects on fruit colour development seem to be implicated rather than secondary factors such as shading. Additional measurements in Hawkes Bay showed that anthocyanin concentrations were not related to changes in chroma, leaf N concentration, or fruit N concentration. Chlorophyll concentration increased with increasing fruit N concentration in individual fruit (r² = 0.35), and this corresponded to decreased red colour intensity (chroma). The relationships explored here explained c. 50–60% of variation in the intensity of red colour. Considered against the survey method and the potential of other factors to affect red colour development, the regressions presented gave insight into ways of managing young ‘Fuji’ trees for increased red colour.

Keywords:

• apple
• Mains domestica
• red colour
• anthocyanin
• chlorophyll
• fruit nitrogen
• leaf nitrogen
• tree vigour
• chroma