Flower Age Affects Fruit Set and Stigmatic Receptivity in Rabbiteye Blueberry

Abstract

Rabbiteye blueberry (Vaccinium ashei Reade) often exhibits problems with low fruit set. Little is known about the duration of flower receptivity in this species. The objective of this study was to investigate the effects of flower age at pollination on fruit set, seed number per fruit, and stigmatic receptivity. `Brightwell' and `Tifblue' rabbiteye blueberry plants were kept under controlled conditions in a growth chamber. Day/night temperatures during pollination were 23 °C/10 °C. Flowers were hand pollinated with self- or cross-pollen at 2-day intervals ranging from 0 to 8 days after anthesis (DAA). Flower age at pollination had a significant effect on both fruit set and seed number per fruit. Rabbiteye blueberry flowers were able to produce optimum fruit set during a period of at least five days. Fruit set was markedly reduced 6 to 8 DAA, depending on the cultivar. Flower age at pollination also had a significant effect on stigmatic receptivity, which was assessed as the number of germinated tetrads on the stigma 24 hours after pollination. Stigmas pollinated 0 DAA had a significantly lower number of germinated tetrads than those pollinated 8 DAA. Flower age at pollination and stigmatic receptivity were positively associated. To our knowledge, this is the first quantitative evidence of delayed stigma maturation in blueberry. Stigmatic receptivity and fruit set were not correlated. Overall, the data strongly suggest that stigmatic receptivity was not a limiting factor for fruit set of `Brightwell' and `Tifblue'. It is hypothesized that ovule longevity determines the duration of flower receptivity in these two rabbiteye blueberry cultivars.