Cell Number and Cell Size in Parthenocarpicvs. Pollinated Blueberry (Vaccinium ashei) Fruits

Gibberellic acid (GA3) promotes parthenocarpic fruit development and is used commercially to increase fruit set in many crops. However, fruit size is usually smaller than that of pollinated fruit. The purpose of this work was to determine the anatomical basis for differences in fruit size between pollinated and GA3-induced parthenocarpic blueberry (Vaccinium asheiReade) fruits. Fresh weights at ripening averaged 1.6 and 2.5 g for GA3-treatedvs. pollinated fruits, respectively. In both pollinated and GA3-treated fruits, mesocarp cell number comprised about 75% of the total pericarp cell number, and increased from ∼7000 cells per cross-sectional area at bloom to ∼9000 at harvest. The duration of the cell division period in pollinated and GA3-treated fruits was similar, with the majority of cell division ceasing by 24 d after bloom (DAB). Cell size in both middle and inner mesocarp of ripe pollinated fruits was significantly larger than in ripe GA3-treated fruits (31000vs. 22000 μm2). Differences in final fruit size between pollinated and GA3-induced parthenocarpic blueberry fruit are due to differences in cell enlargement rather than cell number.