Productivity of ‘Hass’ avocado in central leader highdensity planting systems on ‘Ashdot’ and ‘Velvick’ rootstocks in subtropical Australia

Abstract

Avocados in Australia are commonly planted at low-density, in rows ≥10 m apart and at tree spacings ≥5 m. Yields are low, averaging 10–11 tons per hectare. To improve yield per hectare, we planted a trial in Bundaberg, Queensland, Australia, of ‘Hass’ on two rootstocks, ‘Ashdot’ and ‘Velvick’, in three planting systems with di erent density and treeshaping strategies. The three planting systems were: ‘low-density’ at 9 x 5 m spacing with no canopy shaping and minimal pruning; ‘medium-density’ at 6 x 3 m spacing, conical shaping and pruned to a central leader; and ‘highdensity’ at 4.5 x 2 m spacing, conical shaping and pruned to a central leader and tied to a single-plane 3.5 m tall trellis. Our hypothesis was that more intensive planting with central leader shaping would increase early canopy volume per hectare and improve light distribution in the canopy, with beneficial e ects on numbers of flowering terminals, flowering intensity, fruit set and retention. In the first crop at age 2 years, yield per hectare was highest in the high-density system. However, in the subsequent 3 cropping years, the high- and medium-density systems had equal or lower yields per hectare than the low-density system, despite their higher canopy volumes per hectare. While light distribution within the canopy, numbers of flowering sites and flowering intensity were higher or equal for the higher density systems compared to the low-density system, the rates of spring fruit set and summer fruit retention were lower. Trees on ‘Ashdot’ rootstocks had consistently higher yield and yield e iciency than trees on ‘Velvick’ rootstocks. The higher yields for ‘Ashdot’ appear to be linked to determinate flowering. Reduced canopy size and more branch complexity were also factors in higher yield e iciency from ‘Ashdot’.