Applications of ReTain Reduce Ovule Senescence and Improve Fruit Set in Sweet Cherry

Our previous research revealed that low productivity of several sweet cherry (Prunus avium L.) cultivars is due to the premature senescence of ovules. ReTain^®, is a plant growth regulator with the active ingredient aminoethoxyvinylglycine (AVG) that inhibits ethylene biosynthesis. In this project, we assessed the potential to improve fruit set with applications of ReTain^® to sweet cherry cultivars exhibiting chronically low commercial productivity.  Using ‘Tieton’ and ‘Regina’ trees in both experimental and commercial orchards we conducted rate and timing trials with ReTain®. Three ReTain^® rates were compared (166 g/acre, 333 g/acre and 499 g/acre) with water-treated control trees with applications made at ca. 10% bloom.  The role of application timing was assessed with 333 g/acre of ReTain® applied at ‘popcorn’, 10% bloom, 50% bloom, and full bloom.  Fruit set was determined on two limbs per tree by counting flowers, and fruit just prior to harvest. In addition, ovule viability of flowers was assessed 48 hours after flowers had opened from samples collected 24 hours after ReTain^® treatments were applied at both the first white and fully open stages in the field.  We recorded significant improvements of fruit set from treatment with ReTain^®. At 10% bloom, the highest rate increased fruit set by 124% in ‘Tieton’ and 63% in ‘Regina’. Among all application timings, fruit set at ‘popcorn’ was higher than 10% bloom and 50% bloom timings by 40% and 20%, respectively with a rate of 333g/acre ReTain^®. We documented significant reductions in ovule senescence of ‘Regina’ flowers treated at ‘popcorn’ with 333 and 499 g/acre, and, at ‘full open’ stage with all three rates of ReTain^®. Overall, we recommend single applications of ReTain® at early stages of flowering, with moderate to high rates (i.e. 333 – 499g/acre) to improve fruit set.