Combined effects of ethephon and mepiquat chloride on late blooming, fruit set, and phytochemical characteristics of Black Diamond plum

This study was carried out in 2015 and 2016 to investigate the use of ethephon and mepiquat chloride for reduction of damage to flowering and fruit set caused by late spring frosts in Black Diamond plum. The single treatment of mepiquat chloride delayed full blooming by 5 days, while the ethephon treatment delayed blooming by 7 days. The interactive effect of the chemicals yielded more positive results in the delay of blooming, causing a delay of up to 11 days. An increase in fruit set was observed along with blooming. The fruit set percentage of the control was 4.18%, while it reached 21.28% with the combination of the chemicals. Combined or single applications of the chemicals resulted in a decrease in all phytochemical properties, except for vitamin C. In the control, total anthocyanin, total phenol, soluble solids content, and antioxidant capacity were 67.95 mg 100 mL(-1), 1056.00 mg L-1, 19.68%, and 27.05 mmol L-1, respectively. In the treatment groups these values were reduced to 39.02 mg 100 mL(-1), 854.90 mg L-1,16.98%, and 21.32 mmol L-1, respectively. An ethephon treatment of 4000 ppm led to blighted branches and gummosis. The combined effect of higher mepiquat chloride (150 ppm) and lower ethephon (2000 ppm) doses are believed to contribute to reduction of damage caused by late spring frosts.