Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2014
Publication Date: 5/1/2014
Citation: Sampson, B.J., Marshall-Shaw, D.A., Stringer, S.J., Sakhanokho, H.F., Werle, C.T., Spiers, J.M. 2014. Improving yield and berry quality for zygomorphic blooms of blueberry: the role of the plant growth regulators, gibberellic acid and coconut oil. Scientia Horticulturae. 173:1-14.
Interpretive Summary: A genetic deformity in the blooms of rabbiteye blueberries has been implicated in severe crop losses for susceptible varieties. These floral deformities were thought to reduce fruit set by deterring bee visitation or reducing a bee’s effectiveness for delivering pollen. This was not the case. Deformed flowers were just as productive, and chemicals, such as gibberellins, which we tested to improve fruit set, were very effective a setting sweet, less-seedy berries. A hand-soap made of 100% coconut oil use, which we chose to help uniformly apply the gibberellin solution onto flowers, had some beneficial hormonal effects; it stimulated ovaries to set large, presumably asexually derived seeds and it also accelerated crop ripening. Coconut oil will be tested next season to see if it can set earlier harvests and hasten harvest time, all of which are expected to increase crop revenue.
Technical Abstract: A putative mutant gene(s) induces a high degree of zygomorphy that eliminates or deforms the tubular corollas of rabbiteye blueberries. Once thought to have a benign affect on V. ashei pollination and fruit set, zygomorphy is linked to greater seedlessness, lower fruit set, and is suspected to be a cause of partial crop failures along the US Gulf Coast. Although this trait affects as many as 9 in 10 blooms, it seemingly does not impede pollination or reduce plant fertility. Both zygomorphic and actinomorphic blooms of ‘Premier’, for instance, set comparable fruit loads when cross-pollinated by bees or by humans. However, mean optimal fruit set for cross-pollinated blooms rarely exceeds 60%, except when exogenous gibberellin is applied. This compound boosts fruit set by one-third to ~80% – 90%. Interestingly, GA3 enables V. ashei flowers to set seeds and berries by apomixis and not just by parthenocarpy. In contrast to the large dark-brown pollen-sired seeds of V. ashei, intact seeds of GA3 fruits were pale white or orange in color and 3 – 4 times smaller. The presence of seeds of any size and color is crucial if V. ashei berries are to produce an acceptably high content of sugar. Applying GA3 to pollinated flowers does however delay berry harvest for 3 to 4 days and reduces berry size by 20%. Fortunately, GA3 compensates for smaller berry weight by inducing higher fruit set. Interestingly, coconut oil accelerated berry ripening.