Differences in ovary size among olive (Olea europaea L.) cultivars are mainly related to cell number, not to cell size

Differences in mature fruit size among olive cultivars are related to differences in ovary size at bloom, but it is not known whether cell number or size determines the variation in ovary size. In this study we measured cell size and number in equatorial cross-sectional areas of the principal ovary tissues (mesocarp and endocarp) in eight cultivars with very different fruit and ovary size. The results showed that cell number explained most of the differences in ovary size, while cell size was not related to ovary size, except for a weak (R2 = 0.33) correlation in the endocarp. Since sink strength is thought to be related to cell number, this finding supports the hypothesis that larger ovaries represent stronger sinks. The implications of greater sink strength with bigger ovaries are discussed. Within cultivars, while the cross-sectional areas of mesocarp and endocarp were similar, cell number was higher in the mesocarp but cell size was smaller compared to the endocarp.

• Ovary size was mostly related to cell number both across and within cultivars.
• Mesocarp size was strongly related to cell number, and not at all to cell size.
• Endocarp size was strongly related to cell number, and weakly to cell size.
• Cross-sectional areas of mesocarp and endocarp were similar.
• Mesocarps had more cells of smaller size.