Response of highbush blueberry (Vaccinium corymbosum) 'Spartan' to gibberellic acid and CPPU applied at various rates and timings
Experiments were conducted in 2010, 2013, 2014, and 2016 at an experimental field of Tokyo University of Agriculture, Japan, with highbush blueberry (Vaccinium corymbosum) 'Spartan' to determine the effects of varying the concentration and timing of treatment with gibberellic acid (GA) or CPPU, and to clarify the effects of the combined application of both growth regulators on fruit size and quality. During the initial three experimental seasons, GA was applied at 50, 100, and 200 mg L-1 and CPPU at 5, 10, and 20 mg L-1 on bearing shoots at 0, 5, 10, and 20 days after blooming (DAB). Both GA and CPPU applications led to increases in fruit size, fruit weight, and the number of seeds per fruit compared to untreated controls. Fruit produced on shoots treated with 100 mg L-1 GA was larger than on shoots treated with 50 or 200 mg L-1 GA. GA application was most effective when applied at 5 DAB and was less effective when applied at 0, 10, or 20 DAB. Higher rates of CPPU application resulted in larger fruit. However, malformed (wavy) leaves were observed following CPPU application at 10 and 20 mg L-1. CPPU application was most effective when applied at 10 DAB and was less effective when applied at 0, 5, or 20 DAB. On the basis of these findings, the combined application of 100 mg L-1 GA at 5 DAB and 10 or 20 mg L-1 CPPU at 10 DAB was tested in 2014 and 2016. The treatment resulted in a 1.4- to 1.5-fold increase in mean fruit weight compared to the control, while the soluble solid content and acidity of the fruit were not significantly affected by the treatment. The combined application was considerably more effective than application of GA or CPPU alone in increasing fruit size.
Fujisawa, H., Kawai, Y. and Ishikawa, K. (2018). Response of highbush blueberry (Vaccinium corymbosum) 'Spartan' to gibberellic acid and CPPU applied at various rates and timings. Acta Hortic. 1206, 183-188
acidity, GA, forchlorfenuron, fruit size, fruit weight, number of seeds, soluble solid content