Sampling Apple Trees to Accurately Estimate Mean Fruit Weight and Fruit Size Distribution

in HortScience

Canopies of ‘Gala’ and ‘Fuji’ trees, trained to the vertical axis, were divided into eight vertical sections, each representing 12.5% of the tree canopy. The diameter of all ‘Gala’ fruit and fruit weight for all ‘Fuji’ fruit were recorded for each canopy section. Fruit size from most canopy sections was normally distributed and distributions were similar for most sections. Therefore, fruit size distribution for a tree can be estimated by harvesting fruit from two sections of a tree, representing 25% of the canopy. For small trees in intensive plantings, with canopy diameters less than 2.0 m, average fruit diameter or fruit weight estimated from all fruit collected from 25% of the canopy may provide estimates within 7% of the true value.

Contributor Notes

This research was supported by the U.S. Department of Agriculture National Institute of Food and Agriculture and Regional Research Appropriations under Project 4625 and the Pennsylvania Department of Agriculture Research Program. We acknowledge the valuable contributions of Edwin Winzeler (Penn State Fruit Research and Extension Center) and Dan and Mark Boyer (grower cooperators).

Corresponding author. E-mail: rpm12@psu.edu.

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Article Figures

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    Distributions of fruit diameters, plus normal curves, for fruit diameter harvested from eight sections of ‘Gala’ trees in an orchard in Fishertown, PA, in 2016.

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    Estimated cumulative distribution functions for diameter of fruits harvested from the northeast and northwest sections of ‘Gala’ trees in an orchard in Fishertown, PA, in 2016. The Kolmogorov−Smirnov test statistic (Ksa) of 1.603 is significant at the 0.012 level.

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    Distributions of fruit weights, plus normal curves, for fruit harvested from eight sections of ‘Fuji’ trees in an orchard in Biglerville, PA, in 2016.

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    Estimated cumulative distribution functions (EDF) for fruit weights of fruits harvested from different sections of ‘Fuji’ trees in an orchard in Biglerville, PA, in 2016. The EDFs for various combinations of canopy sections were compared with Kolmogorov−Smirnov two-sample test and the test statistic (Ksa) and P value associated with the test are presented in each figure.

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    Scatter plots of mean fruit diameter and mean fruit weight (FW) estimated from the fruit harvested from a section of the canopy vs. the true mean fruit diameter calculated from all the fruit on a tree. The 45° line is the line of equality on which all points would lie if the estimated value was equal to the true value.

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    The difference between mean fruit diameter (FD) and mean fruit weight (FW) estimated from fruit harvested from three canopy sections vs. the true mean FD or FW for individual whole trees. If the differences are normally distributed, 95% of the differences will lie between the limits of agreement (upper and lower lines).

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    Average difference in ‘Gala’ fruit diameter (mm) or ‘Fuji’ fruit weight (g) between whole trees and various section of the canopy. Dots represent the average difference and asterisks represent the upper and lower 95% confidence intervals. Top figure shows differences for single canopy sections; middle figure shows differences for combinations of two sections; and the lower figure shows differences for combinations of four sections or seven sections. Negative signs before the compass direction indicates a combination of all canopy sections except for the designated section.

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