Severe shoot leaf loss is a source of low quality fruit in kiwifruit vines

Previous studies have shown that photosynthates are translocated considerable distances in kiwifruit vines. However, it has also been demonstrated that fruit in densely shaded areas of the canopy can be of inferior quality to fruit from more open canopy areas. This suggests that in areas of dense shade, fruit are unable to import sufficient carbohydrates to compensate for local scarcity. This trial involved Actinidia chinensis var. chinensis 'Zesy002' vines on an orchard where dense shading within the canopy had resulted in significant leaf drop on some lower-vigour shoots by late summer. Two types of shoots were selected in early autumn: shoots with minimal leaf drop ("healthy"), and shoots that had lost all leaves ("leafless"). Five shoots of each type were evaluated from 22 vines. Fruit quality of the terminal fruit from labelled shoots was assessed at commercial harvest (mid-April). Fruit number shoot(-1), and diameters of the pedicel, shoot base and parent cane internode were also recorded. Fruit quality was significantly worse on leafless shoots, with fruit 14 g lighter, 1.5 percentage units lower in dry matter content and having delayed maturity. The low quality fruit from leafless shoots could be selectively removed prior to harvest to reduce variability in the fruit pool. The reduced photosynthate import into fruit is likely a result of vascular shutdown, but the causal mechanism remains unclear. Future research could provide a clearer understanding of mechanisms that trigger leaf senescence and vascular shutdown, and how these can be mitigated.