EFFECT OF THE GELLING AGENT AND ALTERNATIVE SUBSTRATES ON MICROPROPAGATION OF PEACH ROOTSTOCK GF677 (P. AMYGDALUS × P. PERSICA)

Micro-shoots, originated from axillary buds, were maintained for 1, 3 or 6 sub-cultures (15 days each) in a medium (MS microsalts and organics and QL macrosalts) solidified with washed purified agar (Sigma, A 8678), 5.2 or 4.2 g/L, or agar, 3.2 g/L plus pectines (M-GEL, Switzerland), 8.2 g/L. Significant differences were not detected among the treatments after one sub-culture, but after 3 sub-cultures 4.2 g/L agar induced greater shoot proliferation either than the highest concentration of agar or the combination of agar with pectins. The gelling agent also affected shoot quality: some of the new-formed shoots grown on agar+pectin solidified medium showed a hyperhydric aspect and some chlorotical leaves. Higher water and lower chlorophyll (both a and b) contents were found in those shoots respect to those grown on only agar as gelling agent.
Micro-shoots were induced to root in a medium supplied with 2.5 µM IBA and solidified with 4.2 g/L agar with or without vermiculite and subsequently acclimatised. The rooting percentage was not significantly affected by the presence of vermiculite in the in vitro rooting medium, but root formation was delayed. Micro-shoots induced to root on agar without vermiculite had only a slight lower acclimatisation response.