During the 5th International Conference on Sustainable Agriculture and Biosystem, Researchers in Iran assessed various techniques for producers to consider reasons why fruit and flower losses occur.  Here we delve into the presentation and look at the causes and potential remedies for avoiding flower and fruit losses.

The cultivation of fruit trees holds immense economic significance in many countries worldwide. The production of these trees directly contributes to national income and requires the skilled labour of horticulturists. It involves various elements, including the use of chemical fertilisers, pesticides, modern irrigation systems, tree breeding, and pruning. Fruit trees are not just vital for their economic contributions; they also form the backbone of numerous food industries. Whether consumed fresh or processed, boasts high nutritional value, containing essential sugars, oils, fats, proteins, mineral salts, vitamins, and more.

The Phenomenon of Fruit and Flower Abortion

One of the intriguing aspects of fruit tree cultivation is the phenomenon of fruit and flower abortion. This natural occurrence varies according to species, varieties, environmental conditions, and horticultural practices. Abortion can be either beneficial or detrimental to the tree’s overall yield. When there is an excess of flowers and fruits on a tree, a process known as “natural thinning” occurs, which involves the shedding of some flowers and fruits. However, when there are too few flowers and fruits, abortion can hinder yield and productivity.

The researchers categorised the abortion of flowers and fruits in fruit trees into three main categories:

1. Natural Abortion:  This type occurs due to intense competition among a large number of flowers, which leads to the shedding of a significant proportion of them and newly set fruits. It can exceed 90% in many fruit types, but the remaining fruits usually provide the desired yield. Thinning may be necessary in some cases to ensure adequate nutrition for the remaining fruits and their quality.
2. Abnormal Abortion: This type affects both small and large flowers and fruits and is more harmful to trees for the causes below.
3. Extreme Temperature Abortion: Occurs during hot and dry weather in June and affects most fruit types, usually not significantly impacting the final crop.

Causes of Abnormal Abortion:

1. Environmental Reasons:
   1. Extreme temperatures, both low and high, can cause flower, fruit death and shedding.
   2. Strong winds, especially high dust winds may lead to flower and fruit loss.
   3. Heavy rain and hail can contribute to abortion. 
   4. Intense direct sunlight can cause sunburn, resulting in fruit shedding.
2. Mechanical Causes: Mechanical flower abortion can occur due to severe air currents from pesticide or nutrient spraying operations, often caused by high-pressure spray devices or excessive pesticide doses. 
3. Physiological Reasons:

• • • Lack of pollination and fertilisation in flowers can lead to shedding.
    • Excessive competition among flowers and fruits for nutrients can increase drop.
    • Nutrient deficiencies, such as nitrogen or zinc, may contribute to flower and fruit drop.
    • Irregular irrigation practices, including overwatering, can suffocate roots, leading to flower drop.
    • Shallow soil affects root growth and nutrient absorption, leading to abortion.
    • Unhealthy tree leaves due to disease pressure, insect infestations, or poor growth can increase abortions.
    • Misuse of plant growth regulators or pesticide mixing errors can cause flower abortion.
    • Fungal Infections of flowers and fruits by diseases and insects can cause abortion.
    • Natural fruit ripening and falling from trees can contribute to flower and fruit shedding.

Understanding these causes is crucial for fruit tree growers to employ effective strategies to minimise abortion and enhance fruit yield.

The Science Behind Fruit and Flower Abortion

The physiological process of fruit and flower abortion is closely tied to growth regulators, especially the interaction between two key hormones: auxins and ethylene.   As fruits progress in their growth, the concentration of auxins decreases, while the concentration of ethylene increases and thereby reducing fruit removal force. This hormonal shift causes the separation area between the fruit and the tree to become sensitive to ethylene, ultimately leading to fruit drop. Environmental conditions, such as temperature and humidity, can further exacerbate the issue of fruit abortion.

Remedies for Fruit and Flower Abortion

Several approaches to understanding the problem of fruit and flower abortion in fruit trees may include:

• Fertilisation: Ensuring soil fertility is a vital factor in the flowering and fruit formation process. It’s crucial to apply fertilisers well before the flowering season to allow plants to absorb nutrients, promoting strong flowering. Nitrogen fertilisers, for instance, should be added before flowering and not after.
• Calcium, Zinc and Boron Application: Spraying trees with zinc and boron in specific concentrations, based on tree age, can enhance fruit set and reduce abortion.
• Pruning: Moderate pruning during the winter months helps maintain a balance between vegetative growth and fruit production.
• Tree Girdling: In certain fruit tree varieties where the practice is industry standard like apples and pears, girdling (removing a ring of bark from fruitful branches) during flowering can improve fruit retention.
• Irrigation Management: Avoid excessive irrigation during flowering and fruit set periods to prevent waterlogging.
• Growth Regulators: Application of growth regulators, such as auxins, can delay fruit drop and may assist the duration of flowering.  Seaweed extracts typically contain high levels of auxins, cytokinins and gibberellins.
• Pest Control: Swift pest control measures are essential to prevent infections from escalating.
• Pollination Management: Ensure effective pollination for fruit trees, especially for varieties that suffer from self-incompatibility. This may require the presence of pollinating insects like bees and butterflies.
• Windbreaks: Plant windbreaks around orchards to reduce wind damage, which can contribute to fruit drop.

Understanding fruit and flower abortion in fruit trees is a critical aspect of successful orchard management. While this natural process can be influenced by hormonal changes and environmental factors, effective remedies and horticultural practices can help maximise fruit production and ensure healthy yields. With the right approach, fruit tree cultivation can continue to thrive, providing us with the ability to push quality.

TIP:  Do not spray when flowers are open.  If you need to spray consider before flowers open or after fruit set has occurred.

Links:

• Concentrated Seagold Seaweed Extract
• Nitrogen Fertilisers
• Boron Application
• Calcium Fertilisers
• Zinc
• Soil Test & Leaf Analysis

Flowers and Fruits Abortion in Fruit Trees … Causes and Solutions: A review

• Ahmed F. Z. Al-Dulaimy 1 , Ayad H. Alalaf 2 , R. E. Y. Al-Hayali 3 and D.K.A. ALTaey4 1 Department of Horticulture and Landscape Gardening, College of Agriculture, University of Anbar, Iraq. 2 Department of Horticulture and Landscape Design, College of Agriculture and Forestry, University of Mosul, Iraq. 3 Department of Biotechnology, College of Applied Sciences, University of Fallujah, Iraq. 4 Department of Horticulture and Landscape, College of Agriculture, University of AlQasim Green, Iraq.
• Fifth International Conference for Agricultural and Environment Sciences
• Ahmed F. Z. Al-Dulaimy et al 2023 IOP Conf. Ser.: Earth Environ. Sci. 1158 042010

Read full Article:  https://iopscience.iop.org/article/10.1088/1755-1315/1158/4/042010/meta

Photo credit:  “Olive flower” by grassrootsgroundswell is licensed under CC BY 2.0.