Fruit abscission as related to fruit quality

Many fruit species bear an abundance of flowers which produce a surplus of fruits that the tree is unable to support. In anticipation of this, the major fruit species developed an immature fruit (fruitlet) physiological drop as a self regulatory mechanism. From a horticultural point of view, this self regulating mechanism may be too strong or entirely insufficient. In order to overcome these shortcomings bioregulators are currently used. A more precise understanding of the molecular mechanism underlying natural fruitlet abscission would help in setting up more efficient control strategies. In this context apple fruitlets were assumed as study model. Fruitlet abscission is a highly coordinated event. It involves multiple changes leading to cell separation occurring in specific tissues designated as abscission zones (AZ). Ethylene and IAA regulate abscission. The general interaction between the two hormones is manifested in their antagonistic relationship, where the IAA status of the tissues controls their sensitivity to ethylene. On the other hand, ethylene is a potent inhibitor of IAA action, interfering with its polar transport. In this work the use of a chemical thinner such as benzyl amino purine (BA) was exploited to magnify the normal abscission tendency of lateral fruitlets and to study differences in terms of ethylene biosynthesis between abscissing and persisting fruitlets. Apple trees treated with BA bore lateral fruitlets producing higher amount of ethylene than central ones and displayed an increase in abscission reaching a level 13% higher than untreated trees. The use of 1-MCP nullified BA effect when applied 7 days after cytokinin application, indicating a lag phase between ethylene evolution and fruitlet shedding. Transcript accumulation of MdACS5B and above all of MdACO2 increased along abscission in shedding fruitlets while remained at a basal level in non abscissing ones.