Pruning & Plant Growth Regulators To Increasing Fruit Yield

08/11/19:  Pruning techniques and timing are always a misunderstood practice throughout the olive growing community.  This study is interesting because it delves into simulated mechanical pruning and also introduces the potential use of plant growth regulators.

Pruning is a necessary grove management practice to assist in maintaining appropriate canopy size and promote higher levels of flowering in olive groves.  Recent studies assessing the agronomic responses to mechanical pruning have found that moderate to severe winter mechanical hedge pruning can result in a vigorous vegetative growth response the next season which could reduce subsequent flowering for up to three seasons.

The latest research out of Argentina highlights a potential direction in findings that plant growth regulators need to be assessed in its use for increasing fruit yield.

The study looked at the different techniques for the impact of increasing flowering and fruit yield which included:

  • Tip heading of new shoots
  • Thinning of vigorous new shoots
  • Application of growth regulators – Mepiquat Chloride (MC)

Researchers noted “The thinning of the new water sprouts at pit hardening 4 months after the simulated mechanical winter pruning reduced tree size and improved the return flowering and yield but is time-consuming.  Whilst tip heading was not effective in controlling shoot growth nor promoting flowering on new shoots.”

“The encouraging responses to plant growth regulator on unpruned trees indicate the need for further studies combining winter pruning with MC applications in the 2000–3000 ppm range at pit hardening and at other phenological stages and for several consecutive years to confirm whether this practice is a better post pruning management tool.”

This research is interesting because the use of plant growth regulators could become an important tool for improving flowering and fruit yields.  With the current drought conditions looking at alternative techniques to improve fruit yield could be a game-changer for the Olive Industry and should be explored.

_____________________________________________

Responses of Shoot Growth, Return Flowering, and Fruit Yield to Post-Pruning Practices and Growth Regulator Applications In Olive Trees

Abstract

Winter mechanical hedge pruning of olive trees can result in a strong post-pruning shoot growth response and a low return flowering intensity the following year. However, post-pruning practices including tip heading, water sprout thinning, and the application of the growth inhibitor mepiquat chloride (MC) may positively reduce subsequent vegetative growth and promote flowering. Two experiments were carried out with the aim of addressing the following questions: (1) Do these post-pruning practices applied on trees that received simulated mechanical pruning during the winter reduce growth and increase flowering in the spring of the following year?; and (2) What is the optimal MC dose in unpruned trees needed to increase flowering the following spring? In the first experiment, five-year-old olive trees (cv. Arbequina) growing in a fairly low-density orchard (208 trees ha−1) were hedge pruned at the end of winter using manual clippers on the east and west sides to simulate mechanical disk pruning, and the post-pruning treatments were applied at the pit hardening stage (early summer). In the second experiment, foliar or soil application of MC was performed at pit hardening in unpruned trees. The results show that tip heading of new shoots led to a large number of lateral shoots that flowered little, or not at all, the following spring. In contrast, the water sprout thinning treatment had sufficient flowering to significantly increase fruit number and yield the following year compared to tip heading. Foliar application of MC (1500 ppm) after winter pruning did not inhibit new shoot growth, return flowering was low, and yield was less than the water sprout thinning treatment. The lack of a post-pruning response to foliar MC was likely related to the dose used (1500 ppm). In the second experiment, a foliar application of MC at 3000 ppm was associated with greater return flowering and yield than the untreated control. In conclusion, thinning of vigorous water sprouts at the pit hardening stage three months after simulated winter mechanical hedge pruning can improve fruit number and yield the next year, especially on a per canopy volume basis. Furthermore, the responses to foliar MC application in unpruned trees suggest that more detailed post-pruning studies with MC application doses in the 2000–3000 ppm range and at additional phenological stages should be performed over several consecutive years to assess whether this practice could be a suitable management tool.

Results
The effects of water regimes on the plant water status, photosynthetic performance, metabolites fluctuations and fruit quality parameters were evaluated. All DIS treatments enhanced leaf tissue density, RDI and SDI generally did not affect leaf water status and maintained photosynthetic machinery working properly, while SDIAF treatment impaired olive tree physiological indicators. DIS treatments maintained the levels of primary metabolites in leaves, but SDIAF plants showed signs of oxidative stress.

Moreover, DIS treatments led to changes in the secondary metabolism, both in leaves and in fruits, with increased total phenolic compounds, ortho-diphenols, and flavonoids concentrations, and higher total antioxidant capacity, as well higher oil content.

Phenolic profiles showed the relevance of an early harvest in order to obtain higher oleuropein levels with associated higher health benefits.

Conclusion
Different treatments (or curing methods) that are necessary to remove the bitterness of the raw olive and to stabilize them to obtain edible table olives, causing a loss in phenolic substances which also results in a loss of anthocyanins and antioxidant activity. However, CdN black table olives were the richest in polyphenols, consequently possessing the best antioxidant activity among the analyzed black table olives and among other black table olives reported in literature.  Moreover, it is plausible that regular consumption of CdN table olives can give real returns in terms of prevention of oxidative stress.

Authors: V aleriaAlbarracína1, Antonio J.Hallb, Peter S.Searlesa, M. CeciliaRousseauxa

  • a Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja (CRILAR-Provincia de La Rioja-UNLaR-SEGEMAR-UNCa-CONICET), Entre Ríos y Mendoza s/n, Anillaco, 5301, La Rioja, Argentina
  • b IFEVA, Facultad de Agronomía, Universidad de Buenos Aires/CONICET, Av. San Martín 4453, Buenos Aires, C1417DSE, Argentina

Read the full study at Scientia Horticulture

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