FRUIT COLOR, LEAF NITROGEN LEVEL, AND TREE VIGOR IN FUJI APPLES

A survey of red colour in 'Fuji' apple (Malus domestica Borkh.)fruit f rom trees in orchards situated in three regions of New Zealand has con firmed that tree vigour, tree nitrogen (N) status, and region are impo rtant factors determining the extent and intensity of red colour devel opment. The survey was conducted in Hawkes Bay and Nelson in 1990 and Hawkes Bay and Canterbury in 1991. In both years, a multiple regressio n model using leaf N concentration in February, tree vigour, and regio n as predictors for the intensity of red colour (chroma) gave the best fit to the data (r(2) = 0.65, 1990; r(2) = 0.46, 1991). Interaction t erms for leaf N status and region, and growth rate and region were als o significant. A multiple regression model over both years for Hawkes Bay found leaf N concentration in February and growth rate to be usefu l predictors for chroma (r(2) = 0.66). Leaf N status and tree vigour a ppear to act separately, and direct effects on fruit colour developmen t seem to be implicated rather than secondary factors such as shading. Additional measurements in Hawkes Bay showed that anthocyanin concent rations were not related to changes in chroma, leaf N concentration, o r fruit N concentration. Chlorophyll concentration in with increasing fruit N concentration in individual fruit (r(2) = 0.35), and this corr esponded to decreased red colour intensity (chroma). The relationships explored here explained c. 50-60% of variation in the intensity of re d colour. Considered against the survey method and the potential of ot her factors to affect red colour development, the regressions presente d gave insight into ways of managing young, 'Fuji' trees for increased red colour.