Relationship between shoot leaf area and nut set in hazelnut

The nut set process depends on the availability of viable pollen and the amount of resources, particularly carbohydrates, available during the period of nut growth. One of the usual responses of the plant to pruning is an increase in the rate of nut set. The aim of this work was to investigate the role of shoot leaf area formed by the elongation of the vegetative part of the glomerule on the rate of nut set. Three experiments were carried out on ‘Tonda Gentile delle Langhe’ (TGL) and ‘Negret’ hazelnuts. In the first one, one out of three branches of TGL bushes was removed in addition to current pruning to test the effect of heavy pruning on fruit set. In the second experiment, single glomerules were targeted. Glomerules of different lengths and with different leaf areas were chosen. Some of them were partially defoliated removing 33% (LR33) and 66% (LR66) of the shoot leaf area. In the third experiment, the effect of shoot heading was tested by removing the top 3 nodes (trimming) and heading 2 nodes above the distal glomerule (topping). The pruning treatment resulted in a significant increase of fruit set from 0.54 nuts glomerule-1 in control plants to 1.28 in additionally pruned plants. In the second experiment, nut set rate was 0.92, 1.25 and 1.63 nuts glomerule-1 in control, LR33 and LR 66, respectively. The topping treatment increased glomerule shoot length by 47% and nut set by 78%. These data suggest that the application of horticultural techniques to force the growth of glomerule shoots could improve nut set, which can be considered one of the major barriers to achieving maximum yield potential in hazelnut.