Influence of first season application of paclobutrazol, root-pruning and regulated deficit irrigation on second season flowering and fruiting of mature 'Sundrop' apricot trees

In the orchard in the humid climate of Palmerston North, New Zealand, five-year-old vigorous 'Sundrop' apricot trees on 'Golden Queen' peach seedlings trained on Tatura trellis at 2000 tree ha(-1) were used. The objectives were to evaluate the trees' responses to soil applied Paclobutrazol (PBZ), dormant root pruning and regulated deficit irrigation (RDI). The flowering period for all treatments was monitored at the beginning of the second year of study to evaluate the effect of first year treatments on the time and duration of flowering. The effect of treatments on flower and fruit density and on fruit set was also examined on the experimental trees. In the second year PBZ advanced flowering by 2-4 days, and increased fruit set, final fruit number, crop density and yield efficiency. Root pruning did not affect other flowering and yield parameters, but reduced fruit size in the first season. RDI applied in the first season generally enhanced flowering, flower and fruit density, and especially fruit set and fruit number in the subsequent year. In general, RDI had no negative effect on flowering and fruiting, yield and final fruit size. Both RDI and PBZ had bigger effects on fruit set and fruit number in the second year of treatment. Generally, reproductive growth performed better with PBZ treatment than with root pruning or RDI.