Influence of seed set on apple symmetry assessed by image analysis: an overlooked effect of pollination on fruit shape.

Abstract

The role of pollination ecosystem service on crop yield and some quality parameters have been largely studied. Nevertheless, the effect of pollination on fruit appearance is still a poorly explored field and it has been assessed by means of oversimplified measurements. Here, we developed an image analysis tool to test the hypothesis that pollination greatly affects the symmetry of one of the most consumed fruit worldwide: the apple. The hypothesis was tested for three commercial classes separately, to understand whether the pollination effect was consistent among classes. We also compared the performance of the image analysis tool with a simplified symmetry measurement that has been previously used. Finally, the effect of pollination on apple symmetry was compared with the effect on weight. We quantified the amount of non-symmetrical area of harvested Gala cultivar apples using two-dimension images of fruits sectioned along the longitudinal plane. We showed that increasing pollination led to significant increase of apple symmetry. The image analysis tool resulted more precise to assess the pollination effect on fruit symmetry than the previously used symmetry measurement, leading to the conclusion that pollination effect on apple shape has been probably overlooked because of the use of oversimplified symmetry measures. The effect of pollination on apple symmetry was not consistent among commercial classes since it resulted significant for little and medium size apples but unimportant for large size apples. Differently from the symmetry, apple weight appeared as not influenced by the pollination. Our findings suggest that the effect of pollination on fruit production should be assessed taking into account different variables and different commercial classes of apple.