Endogenous Auxin and Gibberelliu-like Activity in Highbush Blueberry Flowers and Fruit1

Abstract

Abstract ‘Coville’ and ‘Jersey’ blueberry (Vaccinium) flowers and fruit from screened bushes treated with 500 ppm of gibberellic acid (GA) at bloom and from bushes subject to insect pollination were sampled and measured at weekly intervals. Extracts of these organs were partially purified by chromatographic separation on paper, then bioassayed for auxin and gibberellin-like (GA-like) activity. Endogenous levels of both auxin and GA-like substances were higher in ‘Jersey’ than in ‘Coville’ flowers. Auxin concentration in unpollinated flowers was 4 times greater in ‘Jersey’ than in ‘Coville’. A large increase in extractable auxin followed GA treatment in both cultivars. The increase in extractable auxin coincided with the more rapid initial growth rate characteristic of GA-treated fruits. Auxin level coincided with fruit growth rate much better than did level of GA-like substances. By 6 weeks after GA treatment, GA-like substances in the fruits decreased to a level no higher than that in pollinated fruits.