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item Ehlenfeldt, Mark

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Paclobutrazol, a plant growth regulator, was investigated as a means of retarding growth and encouraging greater flower bud development in highbush blueberry. Soil drench application was very effective in increasing floral budset, but it had severe side effects, such as suppression of vegetative buds, that it was judged not suitable. Foliar applications at rates of 0, 5, 10, 50, 100, and 200 ppm showed that applications between 50 and 100 ppm significantly increased budset, without serious side effects. At high concentrations, paclobutrazol, was observed to shorten the number of days to 50% flowering in one case, and to lengthen the time to 50% ripe fruit in another. The effectiveness of paclobutrazol as a growth regulator appears to be affected by plant size, and plant vigor. This information will be useful to blueberry breeders interested in utilizing wild germplasm because such germplasm sometimes flowers poorly.

Technical Abstract: Blueberry cultivars were treated with either soil drenches or foliar applications of paclobutrazol. Soil drenches of 25 mg/L inhibited vegetative shoot elongation and stimulated earlier and greater flower bud production of 'Bluetta', 'Bluecrop', and 'Jersey'. Bud numbers on treated cultivars showed an increase of 359% to 797% over control plants. Significantly higher pecentages of compound buds were also seen on treated plants. The soil drench resulted in reduction of vegetative buds and resulted in overcropping and reduced fruit size. Foliar applications at concentrations of 5, 10, 50, 100, or 200 ppm resulted in increased bud set up to 100 ppm. Treatments did not significantly alter 50% flowering time, in 'Bluecrop' or 'Duke', but induced flowering up to five days ealier in 'Blueray' at 200 ppm. Days to 50% ripe fruit were significantly lengthened at 100 and 200 ppm in 'Bluecrop', due to overcropping, but no delays were observed in 'Blueray' or 'Duke'. Plant size and vigor appeared to be a determining factor in plant response.