Harvest index of apple and kiwifruit – how high can we go by optimising plant architecture and canopy management?

B.M. van Hooijdonk, D.S. Tustin, G.A. Dayatilake, M.J. Oliver, A. Richardson
Efficiency of plant function is measured using harvest index (HI), the fraction of annual fruit dry mass yield divided by the total annual dry mass of tree. HI describes the proportion of total annual biomass allocated into harvestable sinks. The HI of mature apple trees on dwarfing rootstocks is ~60-70%, higher than HI estimates of ~40% for kiwifruit vines. In a recent physiological study using tall spindle ‘Scilate’ (EnvyTM) apple planted intensively on M.9, a mature tree fruit yield of 105 kg tree-1 fresh weight (175 t ha-1 at 1667 trees ha-1) was achieved in the 9th year from planting. Average fruit dry matter content at harvest was 16.2%, suggesting a calculated annual dry weight fruit yield of 17 kg tree-1 (28.3 t ha-1) in the 9th year. This mature tree yield was produced from minimal tree structure compared with traditionally-managed trees; the main axis and branches were slender in girth, and the mean dry weight of winter prunings following harvest in the 9th year was 0.62 kg tree-1. Hence, high fruit yields were associated with little investment in standing tree structure and prunings, implying a very high tree physiological efficiency (HI). The HI of these ‘Scilate’ trees on M.9 in the 9th year was estimated to be 0.81. We speculate that HI of late season cultivars on M.9 could reach 0.85 with further optimisation of canopy management and tree architecture using artificial spur extinction. Exploiting vine architecture and optimising canopy management of kiwifruit may similarly improve yield and fruit quality by increasing vine HI. Preliminary results on whole vine behaviour (flowering, yield and vigour) in response to canopy architectural modification using spur pruning to reduce pruning intensity of ‘Zesy002’ (SunGold®) kiwifruit indicated that spur pruning did not modify yield but reduced vine dry weight of winter prunings by 50% after a single growing cycle. Ongoing work will compare vines managed by spur pruning and replacement cane pruning to quantify budbreak, flowering, yield and fruit quality responses over successive growing cycles.
van Hooijdonk, B.M., Tustin, D.S., Dayatilake, G.A., Oliver, M.J. and Richardson, A. (2018). Harvest index of apple and kiwifruit – how high can we go by optimising plant architecture and canopy management?. Acta Hortic. 1228, 307-314
DOI: 10.17660/ActaHortic.2018.1228.46
Malus × domestica, vigour, roots, shoots, dry weight

Acta Horticulturae