Effects of tetraploidy on olive floral and fruit biology

• Tetraploidy in olive (Leccino cultivar) resulted in larger inflorescences, flowers and ovaries.
• The larger ovaries were made up of larger cells, but in similar number.
• Fruit size was not affected by ploidy, though fruits had much bigger and fewer cells.
• These results shed some light on the effect of ploidy on olive fruit development.
• Results improve understanding of floral and fruit biology and are useful for crop management.

Floral biology and fruit development were studied in Leccino Compact (LC), a polyploid olive mutant of cultivar Leccino (L). This mutant, considered a mixoploid with both diploid and tetraploid cells, has thicker leaves and fruit size similar to the diploid cultivar. So far, no information is available on its floral biology. In this study, the ploidy level of the LC fruit epicarp, analyzed by flow cytometry, was determined to be tetraploid. Pollen size distribution confirmed that most flowers were tetraploid. Morphological and histological measurements of various floral structures and fruits were carried out on the two genotypes, and LC showed larger floral structures (i.e. rachis, flower and ovary) and slightly higher pistil abortion rates. The total number of flowers per inflorescence was not significantly different between L and LC. The large difference (about 2 fold) in ovary cross sectional area between LC and L ovaries was mainly due to increased cell size. LC had slightly larger fruit cross-sectional area (but not greater fruit volume, since LC fruits were less elongated), with much larger cells. Therefore tetraploidy resulted in larger floral structures, as normally occurs in tetraploid plants, but had little effect on fruit size, despite much larger cell size.