Cell number and cell size in parthenocarpic vs. pollinated blueberry (Vaccinium ashei) fruits

Gibberellic acid (GA(3)) 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 GA(3)-induced parthenocarpic blueberry (Vaccinium ashei Reade) fruits. Fresh weights at ripening averaged 1.6 and 2.5g for GA(3)-treated vs. pollinated fruits, respectively. In both pollinated and GA(3)-treated fruits, mesocarp cell number comprised about 75 % of the total pericarp cell number, and increased from similar to 7000 cells per cross-sectional area at bloom to similar to 9000 at harvest. The duration of the cell division period in pollinated and GA(3)-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 GA(3)-treated fruits (31000 vs. 22000 mu m(2)). Differences in final fruit size between pollinated and GA(3)-induced parthenocarpic blueberry fruit are due to differences in cell enlargement rather than cell number. (C) 1997 Annals of Botany Company.