Thinning efficacy of 1-aminocyclopropane-1-carboxylic acid (ACC) in ‘French’ plums

1-aminocyclopropane-1-carboxylic acid (ACC), a precursor of ethylene, has been recently tested as flower or fruitlet thinner in different fruit crops; however, no studies have been reported on Prunus domestica ‘French’ plums.
The aim of this study was to evaluate the efficacy of ACC as chemical thinner when sprayed at different concentrations and phenological stages, during two seasons.
In the first season, 224, 448 and 672 mg L^‑1 were applied at full bloom, shuck split, 8-10 mm fruit diameter or pit hardening.
The thinning response was dependent on the concentration (as higher the concentration, higher thinning), and stage (higher thinning degree at full bloom, independently of the concentration). With respect to this, the phenological stage explained the 49% of the data variation, the concentration the 12.5% and the interaction the 8.52%, being the spray moment more important than the concentration.
During the second season, 112 to 448 mg L^‑1 at full bloom and 448 and 672 mg L^‑1 at 8-10 mm fruit diameter were tested, because these stages were previously detected as the most sensitive.
No differences were detected between ACC concentrations or between stages.
Therefore, the use of ACC in full bloom or in 8-10 mm fruits shows a safety range of use at the concentrations used, which would allow certainty of the expected thinning degree after knowing the fruit set.
Sprays at higher dosage at 8-10 mm fruits diameter showed slight leaf drop but not compromising total leaf area.
When we deduct the effect of crop load on yield efficiency and fruit size, no differences in yield or fruit size were established in both seasons.
Therefore, ACC seems to be a very promising tool as chemical thinner in ‘French’ plums.

V Balkan Symposium on Fruit Growing

V. Beyá-Marshall, A. Verdugo, G. Reginato

Prunus domestica, ethylene precursor, fruit set, European plum

https://doi.org/10.17660/ActaHortic.2026.1449.20