Comparison in Light Condition, Fruit Quality and Photosynthetic Rate between Canopies of 'Fuji' Apple Trees Trained to a Y-trellis and a Central Leader

Abstract

The light condition, fruit quality and photosynthetic rate of 'Fuji' apple trees with the M. 26 interstock trained to a Y-trellis system were compared with those trained to a central leader in order to make clear the superiority of Y-trellis system in the yield and fruit quality.
1. The foliar canopy in the Y-trellis was V-shaped, the leaves covered the ground surface area evenly; whereas, the canopy of the central leader tree was cylindrical and the leaves were concentrated around the trunk.
2. The survey blocks (foliar zones) with more than 20% relative illuminance were distributed evenly over the entire canopy in the Y-trellis, whereas those of the central leader tree were concentrated in the periphery of the canopy; hence, the canopy of the Y-trellis was superior to that of the central leader for light interception.
3. Percentage of soluble solids content in the fruit from the Y-trellis was higher than that harvested from the central leader tree. The brix of fruit exposed to relatively intensive illumination tended to be higher than those growing in the shade.
4. There was a significant positive correlation between PPFD (photosynthetic photon flux density) and photosynthetic rate.
5. We conclude that, in spite of the smaller leaf area index (LAI), the higher photosynthetic rates on trees trained to the Y-trellis give rise to a superior yield.