Early Fruit Size Prediction Model Using Cubic Smoothing Splines for ‘Washington Navel’ (Citrus Sinensis L. Osbeck) Oranges in Australia

Citrus growers need to be able to determine the expected fruit size and the proportion of export-quality fruit at harvest relatively early in the growing season. Early fruit size prediction would also help in planning harvest operations and administering marketing strategies well in advance. This will also enable growers to remove small fruits that would not attain the desired export size. Fruit diameter growth of ‘Washington Navel’ oranges was measured over three consecutive growing seasons during the Stage II (cell enlargement) period between January and July. Fruit were randomly selected from around the tree canopy and tagged to measure the fruit diameter at fortnightly intervals until harvest. The data were used to develop a fruit size prediction model using cubic smoothing splines. The model was able to predict the final fruit size and the final percent size distribution at early stages of fruit development in January/February in Australia. Results indicated that under the growth patterns shown by na...