A time-course model for BA action in apple fruitlet thinning

Benzyladenine (BA) is a well known synthetic cytokinin broadly used as a thinning agent in apple orchards. BA has numerous physiological effects, strictly dependent upon the tree developmental stage, the concentration of the chemical and the environmental conditions at the time of spraying. The enhanced ethylene evolution observed in BA-treated apple leaves and fruits may be one of the key factors that trigger the physiological processes leading to fruitlet abscission. In order to shed light on the ethylene-related events occurring during abscission, a timecourse model for BA action was developed based upon physiological data obtained by combining the use of BA either with AVG (aminoethoxyvinylglycine), or 1-MCP (1-methylcyclopropene), blocking ethylene biosynthesis and perception, respectively. The results confirm the bimodal action of BA through ethylene, acting first on shoot growth and then, most likely indirectly, promoting fruitlet abscission. Based on a 24 hours-resolution time-course, a very fast action of BA was observed within 24 h from the treatment. A parallel antagonist effect was exerted by AVG within 24-48 h. This model, currently under validation, was confirmed to be a very reliable system for studying fruitlet abscission in apple.