Topological and spatial analysis of within-tree fruiting characteristics for walnut trees

Shoot morphology and canopy position usually have a significant impact on fruiting potential, but these effects have not been fully quantified, especially at the whole tree level. This study addressed the fruit number variation as affected by shoot length and within-tree position for mature walnut trees cv. Chandler, which is a lateral bearing variety. A positive relationship was observed between parent shoot (previous-year) length and the number and length of current-year floral shoots, as well as between the length of current-year floral shoots and fruit number per floral shoot. Fruit number and spatial position in defoliated trees were manually identified based on LiDAR data, but tree architecture, including shoot length and topology, was not accurate to be reconstructed by the available software (TreeQSM). About half of fruits were located in the outer canopy, while the reminder, especially at the mid-canopy height, were equally distributed inside the canopy to a depth of about 90 cm. The topological fruit location at the whole tree level were manually quantified in relation to the length and relative node rank of parent shoots. Even though long parent shoots exhibited more lateral bearing, the majority of fruits at the whole tree level were on current-year floral shoots that developed from the terminal buds of relatively short (<=10 cm) parent shoots because these represented the vast majority (over 90%) of parent shoots on mature trees.

Automated summary

Shoot morphology and canopy position play a significant role in fruiting potential. This study focused on the relationship between shoot length and within-tree position and fruit number variation in mature walnut trees. Fruit number was positively correlated with the length of previous-year shoots and current-year floral shoots. However, accurately reconstructing tree architecture using available software proved to be challenging.