Illuminating the relationship between canopy light relations and fruit yield in apple planar cordon orchard systems

In apple orchards, total dry matter production and fruit yield are positively related to total seasonal canopy light interception and full-canopy fractional light interception. High within-canopy irradiance is central to achieving optimal spur function and high fruit quality. In New Zealand, modern mature high-density apple orchards intercept 55 to 60% of incoming light. New planar cordon systems have been designed aiming to improve light interception and distribution, to increase yield ha^‑1 and fruit quality well beyond that of current best commercial practice. Prototype systems planted in 2014 compare commercial genotypes (‘Royal Gala’ and ‘Scifresh’ (Jazz™)), planted at either 2.0 or 1.5 m between rows (tree densities of 1667 to 2222 trees ha^‑1, respectively) with upright fruiting stems either vertically oriented or inclined in a narrow vee. We have little knowledge of the light interception and distribution characteristics of these planar cordon systems, other than their design being based on hypotheses of the relationships between canopy light relations, fruit yield, and fruit quality. In the ‘Royal Gala’, as early as their 4^th leaf, the fruiting shoot canopy reached ~3.1 m in height and the lower half of the canopy was in full production. Whole canopy fractional light interception (~54-70%) equalled or exceeded the same seasonal maxima as current mature commercial tall spindle orchards. Fruit yield in these immature canopies ranged from 81 to 105 t ha^‑1. This provided the first opportunity to investigate light distribution within the canopy. Within-canopy irradiance and whole-canopy light interception are discussed in relation to components of yield.