Influence of plant growth regulators on growth and formation of sylleptic shoots in one-year-old apple cv. Gala Mast

Aim: To examine the effectiveness of 6-benzyladenine (BA) alone or in combination with gibberellic acid (GA3) on sylleptic shoots formation on one-year-old apple cv. Gala Mast grafted on MM-106 rootstock. Methodology: During the second vegetative period, the actively growing apical portion of the nursery tree was sprayed with varying doses of BA and BA+GA3 (200, 300, 400, 500, 600, and 700 ppm) using a hand sprayer until run-off. Three spray treatments were performed at one week apart. The first spray was applied when the growth of the central leader reached 70-80 cm. Results: All plant growth regulators treatments significantly increased the number and length of sylleptic shoots, branching zone and per cent branched trees compared to control. The unsprayed trees had an average of 1.95 useful sylleptic per tree, 1.1 m total sylleptic shoot length, 10.24 cm branching zone and 35 per cent branched trees. Application of BA (700 ppm) resulted in four-fold increase in the number of sylleptic shoots (7.8), more than two-fold increase in total length of sylleptic shoots (2.44 m), and around four-fold increase in branching zone (38.96 cm). The 100 per cent branched trees were obtained with the application of BA (500, 600, 700 ppm) and BA+GA3 (600, 700 ppm) in both experimental years. Moreover, these treatments obtained 2.78 to 2.90 values of the trunk and mean sylleptic shoot diameter ratio. Interpretation: Application of BA alone or in combination with GA3 played an important role in overcoming apical dominance and therefore in the production of well-branched apple nursery tree. However, application of BA alone has a stronger positive effect on sylleptic shoot formation. More than 400 ppm BA appears to give a significant stimulation for the production of sylleptic shoots, with the highest beneficial effect reported with the application of 700 ppm BA. However, it is cost-effective to apply 3 sprays of 500 ppm BA for adequate growth and sylleptic shoot production. Key words: 6-benzyladenine, Gibberellic acid, Nursery tree, Plant growth regulators, Sylleptic shoot