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FORECASTING HARVEST FRUIT SIZE DURING THE GROWING SEASON
As this requires measuring a direct accessible factor, the largest diameter of the fruit was measured.
To calculate fruit weight we used a transformation function between diameter and weight which takes into account that fruit form index changes during the fruit development.
The model FRUZU (Winter, 1969) which is used in Bavendorf for fruit size prognosis does not need transformation during the growing season, because it predicts fruit size at harvest time based on growing functions for fruit diameter which are adjusted by fruit set density parameter.
Transformation is only needed for receiving yield data.
Regression calculations on JONAGOLD fruit growth measurements showed that an early bloom is followed by low temperatures during the cell division period and does not affect the fruit size at harvest time, but changes the growing function during the season.
This indicates that, aside from fruit set density, temperature and day length may change fruit growth and therefore should be used in a growth prognosis model.