Effect of ascorbic acid and citric acid on ex vitro rooting and acclimatization of Prunus avium L. microshoots

Ex vitro rooting is usually a cost- and labor-reducing technique in micropropagation cycle. The role of externally applied vitamins in ex vitro rooting and establishment of sweet cherry microshoots was studied. Microcuttings; of the Estonian sweet cherry cultivar 'Kristiina' were sprayed daily with ascorbic acid or citric acid solutions in concentrations of 0, 0.1, 0.5 or 1.0 mM. The highest survival (56%) was recorded on plantlets sprayed daily with 0.5 mM ascorbic acid. Other concentrations did not affect the establishment of explants. Among explants treated with citric acid the highest survival (46%) occurred at 1.0 mM. The effect of lower concentration (0.5 mM) was insignificant. The highest dry weight of shoots (0.0458 g) and roots (0.02487 g) was measured for the 0.5 mM ascorbic acid treatment. On treatment with 1.0 mM citric acid the shoots developed well and formed roots but overall root dry weight remained lower than on untreated explants. The results indicate that the selected concentrations of citric acid were probably too low. The ex vitro rooting and survival of sweet cherry microshoots can be promoted by applying low doses of ascorbic or citric acid during the whole establishment phase in greenhouse.