Fruit growth and sink strength in olive (Olea europaea) are related to cell number, not to tissue size.

The relationship between tissue (mesocarp and endocarp) growth and either tissue initial (i.e. in the ovary at bloom) size or cell number was studied using the olive cultivar Leccino (L) and its mutated clone (LC), which produces tetraploid fruits. LC ovaries were 2.7 times the volume of L ovaries, but contained an overall similar number of much larger cells. This allowed decoupling cell number and ovary size, which are normally closely correlated. With this decoupling, cell number in the ovary correlated with tissue growth in the fruit while tissue size in the ovary did not. Cell size in the ovary was inversely correlated with the tissue relative growth from bloom to harvest (i.e. the ratio between final and initial tissue size). These results support the hypothesis that cell number and not tissue size are related to fruit growth and sink strength, and that cell size in the ovary tissues is a good predictor of tissue growth, across cultivars and tissues, even when cell size is strongly affected by ploidy.