Apple fruitlet ethylene evolution and MdACO1, MdACS5A, and MdACS5B expression after application of naphthaleneacetic acid, 6-benzyladenine, ethephon, or shading

Abstract

Abscission of apple (Malus xdomestica Borkh.) fruitlets is associated with increased ethylene evolution, although the role of ethylene is not clear. Fruit let ethylene evolution and expression of ethylene-related MdACO1, MdACS5A, and MdACS5B genes were followed in the abscission zone (AZ) and fruit cortex (FC) of king and lateral fruitlets of 'Golden Delicious'/M.9 after spraying with 15 mg-L-1 naphthalene acetic acid (NAA), 150 mg-L-1 6-benzyladenine (BA), 500 mg-L-1 ethephon, and after 3 days 96% shading, all applied at a mean 10 mm fruit let diameter. Lateral fruitlets (LF) were more susceptible to abscission after treatment with chemical thinners or shading compared with king fruitlets (KF) in which only ethephon-treated KF abscised later. On KF, only ethephon increased fruit let ethylene evolution, MdACO1 expression in FC and AZ 8 days after treatment (DAT), and abscission of KF 10 DAT, but the other treatments did not. Although ethephon increased MdACO1 expression in FC of KF 8 DAT, the expression of MdACS5A and MdACS5B remained unchanged. On LF, all treatments at 8 DAT increased ethylene evolution and MdACO1 expression in FC and enhanced abscission 10 to 22 DAT. Expression of MdACS5A and MdACS5B in FC of LF 8 DAT was expressed at a lower level compared with MdACO1. In the AZ of both KF and LF, only ethephon increased expression of MdACO1, MdACS5A, and MdACS5B.