Mechanical pruning attenuates alternate bearing in ‘Nadorcott’ mandarin

Abstract

In Citrus, certain species and/or cultivars are prone to alternate bearing, i.e., a year of heavy crop (ON year) is followed by one of low flowering and light crop (OFF year), and vice-versa. To counteract the fruit effect, we propose a guided mechanical pruning initiated in the spring of an ON year and carried out annually. Our hypothesis is that this gives rise to abundant shoots with well-developed leaves that reach the floral bud inductive period ready to receive the inductive signal and, thus, to induce the bud to bloom the following spring.The experiment was carried out during four consecutive years (2013–16) using a commercial plantation of ‘Nadorcott’ mandarin in southwest Spain. Trees were mechanically pruned: hedging (H) or topping by completely removing the upper shoots of the canopy (T) or by cutting ½ of their length (T½). Unpruned trees were used as controls. The experiment began in the spring of an ON-year.T and T½ carried out in the spring restart the meristem and give rise new shoots that develop in summer and autumn. At the inductive period, the leaves on these new shoots showed a CiFT2 gene expression 4- and 3.7-fold higher than their respective old leaves. In the case of the T½ their buds avoided the inhibitory effect of the fruit and bloomed the following spring even with the fruit in the cut-back shoot. For the two periods of ON-OFF years of our experiment, cumulative yield of the T treated trees barely increased, whereas T½ significantly increased with respect to the unpruned trees.We conclude that cutting flowering shoots annually in half-length by means of mechanical pruning (T½), attenuates alternate bearing behaviour in 'Nadorcott' mandarin. In this experiment, cumulative yield increased by 25% with regard to unpruned trees during the four years of the trial.