Carpel Polymorphism in Citrus Fruit

Each citrus species and cultivar in the Aurantioideae exhibits a distinct range of carpel (segment) numbers within their fruits. The observed range of segments for fruit within any species or cultivar can be influenced by branch location on a tree. The carpel number for all fruits produced on a single tree may have a symmetrical, unimodal distribution, as well as a positively or negatively skewed unimodal distribution. Most citrus species produce fruits that contain eight to ten segments. However, the average segment number per fruit may be as high as 17 in some pummelos (Citrus grandis [L.] Osb.) or as low as four in some kumquats (Fortunella japonica [Thumb.] Swing.). Correspondingly, pummelos are the largest citrus fruit in terms of fresh weight and diameter, while kumquats are the smallest. Fruit geographical orientation on the tree does not affect the segment number. Abscission of fruit does not select for any particular segment number. Crossing parents with dissimilar fruit segment numbers produces progeny with a range of segment numbers.