Predicting fruit skin background colour retention using fruit nitrogen content in ‘Conference’ pear

Green fruit skin background colour is a key quality attribute of ‘Conference’ pear. Fruit which develop a yellow background colour during long-term storage incur a price penalty. Fruit nitrogen (N) content at harvest is positively correlated with colour retention during storage. However, substantial spatial and seasonal differences in fruit N content can occur in a single orchard. This 4-year study in irrigated, non-irrigated and fertigated orchards on a total of over 250 plots further explores the relation between fruit mineral composition, green colour retention during storage and tree vegetative and generative development. While fruit N content has a highly significant effect on colour retention, actual predictive modelling of colour retention based on fruit mineral composition and standard quality assessments available at harvest (fruit firmness, Brix value and starch index) is currently too inaccurate for practical purposes. As such, a ‘N threshold’ approach is the most sound approach to assess the risk of poor fruit skin background colour retention. The saturation-curve type logistic relation between fruit N content and fruit skin background colour allows for improved use of this approach in planning long-term storage, with treshold N levels >50 and >55 mg 100 g^‑1 fw for 4 and 6 months of ULO storage, respectively. Low fruit N content often coincides with low vegetative growth and high numbers of flower clusters per tree. Breaking this repeating cycle is necessary in affected orchard zones.