Apple Tree Crop Loads Affect Trunk Growth, Future Harvests, and Fruit Quality

Jenn Hoskins
31st May, 2024

Apple Tree Crop Loads Affect Trunk Growth, Future Harvests, and Fruit Quality

Increasing the total crop load on Malus domestica trees causes a linear reduction in the trunk's relative growth rate, which approaches zero at the highest fruit densities.

Image adapted from: Scalisi et al. / CC BY (Source)

Key Findings

  • The study was conducted on 'Ruby Matilda' apple trees in Victoria, Australia, to improve crop load management
  • High crop loads increased yield but reduced trunk growth and return fruit set
  • Optimal crop load of about 6.8 fruit per cm² of leader area ensures consistent fruit set and good quality
The study conducted by Agriculture Victoria Research focuses on improving precision crop load management in narrow-canopy, multi-leader apple trees, specifically in ‘Ruby Matilda’ apples (marketed as Pink Lady®). The research aimed to determine the effects of different crop loads on the growth, yield, and fruit quality of individual leaders and the overall tree over three years[1]. Apple trees are often susceptible to biennial bearing, a phenomenon where high yields in one year are followed by low yields in the next. This irregular fruiting pattern can cause significant economic losses[2]. Previous studies have shown that this pattern is influenced by various factors, including the presence of fruit, which can inhibit floral induction and lead to reduced yields in subsequent years[2][3]. In this study, researchers imposed different crop loads on the primary and secondary leaders of bi-axis apple trees to observe the effects on trunk growth, return fruit set, yield, and fruit quality parameters. They found that high crop loads on individual leaders significantly increased yield but also reduced trunk growth and return fruit set. Additionally, high crop loads led to a deterioration in several fruit quality parameters, except for flesh firmness and starch index. Interestingly, the study observed that high crop loads on secondary leaders had moderate negative effects on the primary leaders' trunk growth, yield, and fruit mass. However, it only marginally affected the primary leaders' return fruit set and did not significantly impact their fruit quality. This indicates that while the crop load on one leader can influence another, the effects are not uniformly detrimental. The research identified an optimal crop load of approximately 6.8 fruit per cm² of leader cross-sectional area to achieve a consistent return fruit set within the same leader. At the whole-tree level, a similar crop load of 6.9 fruit per cm² of trunk cross-sectional area was found to produce a consistent return fruit set, albeit with higher variability. These crop loads resulted in high yields (120 and 111 t ha−1, respectively) and good quality fruit. This study's findings align with earlier research that highlighted the complex interplay between fruit presence, leaf presence, and hormonal signals in regulating floral induction and fruit growth[3]. The localized approach to fruit thinning, focusing on individual leaders as management units, simplifies operations and reduces variability, making it a practical solution for orchard management. Moreover, the study contributes to our understanding of the physiological processes underlying biennial bearing. Previous research suggested that phytohormones exported from fruit could suppress flower bud formation, leading to biennial bearing[4]. This study supports the idea that managing crop load at a localized level can mitigate some of these effects, leading to more consistent yields. In conclusion, the research conducted by Agriculture Victoria Research provides valuable insights into precision crop load management in narrow-canopy, multi-leader apple trees. By focusing on individual leaders, orchard managers can achieve high yields and good quality fruit while minimizing the negative effects of high crop loads on tree growth and return fruit set. This localized approach offers a practical solution to the challenges of biennial bearing and variability in apple production.

FruitsAgriculturePlant Science

References

Main Study

1) Localised and tree total crop loads influence trunk growth, return fruit set, yield, and fruit quality in apples

Published 30th May, 2024

https://doi.org/10.1007/s44281-024-00045-4

Related Studies

2) Genetic control of biennial bearing in apple.

https://doi.org/10.1093/jxb/err261

3) Impact of Within-Tree Organ Distances on Floral Induction and Fruit Growth in Apple Tree: Implication of Carbohydrate and Gibberellin Organ Contents.

https://doi.org/10.3389/fpls.2019.01233

4) Profiling of phytohormones in apple fruit and buds regarding their role as potential regulators of flower bud formation.

https://doi.org/10.1093/treephys/tpac083


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