Modeling of ‘Gala’ apple fruits diameter for improving the accuracy of early yield prediction

• The effect of fruit load and position on fruit growth was studied in 2009–2011.
• Gompertz function – models was developed for high-, middle- and low-loaded trees.
• Investigated models estimated the actual fruit growth successfully in most cases.
• Best models enable accurate forecasting of the ‘Gala’ apples yield.

A long-term growth curves usually describes the development of fruits insufficiently for a particular season hence it might cause severe discrepancies between the forecasted and harvested characteristics. For improving the early yield forecasts of ‘Gala Schniga’/MM9 apples (Malus × domestica Borkh) the diameter of fruits on different abounded trees; low (L) 4 fruits/cm2, medium (M) 7 fruits/cm2 and high (H) 9 fruits/cm2 was measured in three successive growing seasons (2009, 2010 and 2011) every two weeks from the T-stage till picking fruits. The fruits’ development was observed on the terminal (TL), 2-years (2L) and 3-years old shoots (3L). The input data were transformed over natural logarithm and regression analyzes into modified Gompertz function (models) describing the fruit growth on different abounded trees and different position of shoots on the trees. The use of specific models improves annual yield forecasts of 28 commercial ‘Gala’ orchards over the long-term model significantly. On that way the minimal difference of 200 kg/ha was calculated with middle-loaded 2L model in 2009, 510 kg/ha with low-loaded TL model in 2010 and 156 kg/ha with middle-loaded 3L model in 2011, respectively.