Variance components of fruit quality - a 'Golden Delicious' case study in South Africa

Fruit maturity and fruit quality are important horticultural parameters that are of commercial value and demanded by the consumer. The identification and magnitude of the factors contributing to fruit-to-fruit variability in maturity and quality are not always known to the producer and this missing information may complicate decision making and optimisation of pre-and postharvest practises. To analyse the variability in fruit maturity and quality, 14 'Golden Delicious' orchards were selected in each of two climatic contrasting areas and five variables (starch conversion, firmness at harvest, firmness after storage, lightness at harvest and lightness after storage) were measured on all the fruits from two scaffold branches (top and bottom of the tree). The variance in the data was assigned to seven different components (region, orchard, tree, vertical position in the tree, light exposure and bearing wood). Variance that could not be assigned was pooled as “not explained”. Effects, interactions and correlations were calculated amongst the variables and components. Orchard difference was the biggest contributor of variability in all the variables, especially starch conversion, where it was found that the actual starch levels of the fruit at harvest were very different from the mean level calculated to predict harvest release date. Firmness variability was not well described by the components and correlated poorly with starch levels at harvest. Results from both peel lightness (lightness value) and starch conversion at harvest suggested that producers in the Koue Bokkeveld region would benefit from segregating the top and bottom fruit at harvest while Elgin producers can sort starch conversion by segregating sun exposed and shaded fruit. It was also found that lightness at harvest correlates well with lightness after storage but poorly with firmness suggesting that postharvest lightness sorting should result in homogenous lightness batches after storage but the firmness will be variable. Understanding the magnitude of different preharvest aspects towards the variability in fruit maturity and quality gives direction to the development of pre- and postharvest horticultural practices that can lead to increased Class 1 pack outs and uniformity in fruit quality post storage.