Effect of different benzyladenine time pulses on the endogenous levels of cytokinins, indole-3-acetic acid and abscisic acid in micropropagated explants of Actinidia deliciosa

Actinidia deliciosa apical shoots were cultured in MS liquid medium with different benzyladenine (BA) pulses and using cellulose plugs as support for the explants. Abscisic acid (ABA), indole-3-acetic acid (IAA) and some cytokinins (Cks) [zeatin (Z), dihydrozeatin (DHZ), zeatin riboside (ZR), dihydrozeatin riboside (DHZR), N6-isopentenyladenine (iP) and N6-isopentenyladenosine (iPR)] levels were measured in leaves from explants cultured both in the absence and in the presence of BA (4.4 μM) for 30 min, 1, 2 and 35 d. Analyses were carried out after three subcultures at the end of the multiplication phase and after 31 d in ex vitro conditions. A clear relationship between the endogenous content of phytohormones and the growth characteristic of kiwifruit microplants could be confirmed. Microplants with the best growth characteristic were those cultured in presence of BA during 1 d. They were characterised by higher contents of IAA than the others studied, as well as by higher values in the IAA/Cks and IAA/ABA ratios, both at the end of the multiplication phase and after the acclimatisation period. Taken all together, these ratios at the end of the multiplication phase could be used as growth indicators of A. deliciosa explants behaviour under ex vitro conditions.