The Diverse Applications of Ethylene in Agriculture

Ethylene is a naturally occurring gaseous plant hormone – just two carbon atoms bonded with four hydrogen atoms – yet it plays an outsized role in agriculture. From triggering the ripening of bananas in commercial chambers to helping citrus fruits shed their green skin before reaching supermarket shelves, ethylene is one of the most widely used growth regulators in modern farming. Its applications span the entire production chain, from field to post-harvest facility, and understanding these uses is essential for anyone involved in crop management or food supply logistics.

Ethylene as a ripening agent for climacteric fruits 🔗

The most well-known use of ethylene in agriculture is as a ripening agent for climacteric fruits. Climacteric fruits – including bananas, tomatoes, mangoes, avocados, and pears – continue to ripen after they are harvested. This ripening is driven by a natural spike in ethylene production and an elevated rate of respiration. Non-climacteric fruits, such as grapes and strawberries, do not exhibit this post-harvest ripening behaviour and must be harvested when already ripe.

In commercial practice, climacteric fruits are often picked at the mature-green stage so they can withstand transportation over long distances. Once they arrive at a distribution centre or ripening facility, they are exposed to controlled concentrations of ethylene gas in sealed rooms. This triggers the conversion of starches to sugars, the development of aroma volatiles, the softening of flesh, and the change in skin colour – all the hallmarks of a ripe fruit.

Bananas are a prime example. They are harvested green in tropical regions and shipped across the world. At destination, they are placed in pressurised ripening rooms and treated with ethylene alongside controlled temperature and humidity. The result is uniformly ripe, yellow bananas ready for retail. Similarly, tomatoes are frequently harvested before full colour develops. External ethylene application accelerates pigment changes – the loss of green chlorophyll and the accumulation of red lycopene – without fundamentally altering the fruit’s internal quality.

Two common methods of ethylene application 🔗

There are two standard methods for applying ethylene in ripening chambers. In the shot system, a concentrated dose of ethylene gas is introduced into a sealed chamber all at once, and the environment is then maintained at set temperature and humidity levels to allow uniform ripening. In the trickle system, low concentrations of ethylene are released continuously or at intervals over a longer period. The trickle method provides more precise control and is often preferred for large-scale operations because it reduces the risk of over-ripening.

Ethylene products are registered for use on a wide range of crops. According to a USDA technical report, ethylene is labelled for ripening avocados, kiwis, melons, mangoes, papayas, pears, persimmons, pineapples, stone fruits, tomatoes, and other fruiting vegetables. It is also approved for sprout suppression in stored potatoes and for accelerating flue curing of tobacco.

Flower induction in pineapple 🔗

Beyond fruit ripening, ethylene has a critical role in flower induction, particularly in pineapple cultivation. Pineapple is a non-climacteric fruit, but its vegetative-to-reproductive transition is governed almost entirely by ethylene. A small burst of ethylene in the shoot apical meristem signals the plant to start flowering.

Commercial pineapple growers exploit this mechanism to synchronise flowering across entire fields. By applying ethephon (2-chloroethylphosphonic acid), an ethylene-releasing compound, to the central cup of the plant, growers ensure that all plants flower and fruit at roughly the same time. This synchronisation is vital because it enables a single harvest pass, reducing labour costs and simplifying logistics. Without ethylene forcing, pineapples would flower at irregular intervals based on natural environmental cues like cool temperatures and shorter days, making harvest unpredictable.

In fact, the prevention of premature natural flowering is just as important as its induction. Uncontrolled ethylene production triggered by weather changes can lead to what the industry calls Natural Day Flowering (NDF), resulting in unsynchronised fruit development and economic losses. To manage this, growers use ethylene biosynthesis inhibitors like aminoethoxyvinylglycine (AVG), which block unintended ethylene production until the desired flowering window.

Shuck loosening in nut crops 🔗

Ethylene also plays a practical role in nut harvesting, particularly in walnut and pecan production. In walnuts, the hull (or shuck) surrounds the shell and must split open before the nut can be efficiently harvested. Ethylene naturally rises in concentration as the kernel matures, contributing to hull cracking and separation from the shell.

Growers can accelerate this process by applying ethephon at or shortly after kernel maturity. According to the UC Davis Sacramento Valley research team, ethephon application can advance walnut harvest by four to seven days depending on variety and season, while also improving kernel colour and potentially reducing insect damage. The compound increases cellulase activity in the cell walls of the hull, helping to disintegrate cellulose and speed up dehiscence in green walnuts.

In pecans, the shuck-split process is a coordinated hormonal event. As the kernel fills completely, levels of the growth promoter indole-3-acetic acid drop, while abscisic acid and ethylene concentrations increase. Ethylene must reach a critical internal threshold before shuck opening can begin. While external ethephon treatment is sometimes used to promote uniform splitting, careful water management during nut maturity is equally important – drought stress can delay shuck opening and lead to quality losses.

Degreening of citrus fruits 🔗

Many citrus fruits are internally ripe while their peel is still green, especially in tropical and subtropical growing regions where nighttime temperatures don’t drop enough to break down chlorophyll naturally. This presents a marketing challenge – consumers associate green-skinned oranges or lemons with unripeness, even when the fruit inside is perfectly edible.

Ethylene degreening solves this problem. When applied to harvested citrus fruits, ethylene triggers the destruction of green chlorophyll pigments in the peel and promotes the accumulation of yellow and orange carotenoid pigments. The result is the vibrant colour consumers expect.

At the molecular level, ethylene induces the synthesis of chlorophyllase, the enzyme that catalyses the first step in chlorophyll breakdown. Research published in the Proceedings of the National Academy of Sciences demonstrated that ethylene-treated citrus fruit showed a five-fold increase in chlorophyllase activity within 24 hours. The enzyme cleaves the phytol chain from the chlorophyll porphyrin ring, initiating the visible loss of green colour.

Importantly, ethylene degreening primarily affects the peel. Studies have found that it has no significant effect on the internal quality indicators of citrus – including total soluble solids, acid content, or bioactive compound levels in the juice. This means the treatment improves visual appeal without compromising taste or nutritional value.

Recommended degreening conditions 🔗

The optimal conditions for degreening vary by region. In Florida, where rapid chlorophyll breakdown is prioritised, degreening is typically carried out at 28-29°C with 90-95% relative humidity and 3-5 ppm ethylene. In California, Israel, and Spain, lower temperatures of 21-25°C are used to allow both chlorophyll degradation and some carotenoid synthesis simultaneously. Packers must balance speed of colour development with the risk of enhanced decay and peel disorders that can accompany prolonged ethylene exposure at high temperatures.

Facilitating leaf and fruit abscission for mechanical harvesting 🔗

One of the more practical agricultural applications of ethylene is in promoting abscission – the natural separation of plant organs such as leaves, fruits, or flowers from the parent plant. Ethylene stimulates the formation of an abscission zone, a layer of specialised cells at the junction where a leaf or fruit attaches to the stem. When this zone develops fully, the connection weakens and the organ detaches cleanly.

This process is commercially valuable because it makes mechanical harvesting far more efficient. In citrus production, pre-harvest application of ethephon can reduce the force needed to detach fruit from the tree, enabling machines to collect produce without excessive damage to the fruit or the tree. Ethephon is also used as a harvest aid in macadamia production, where it can increase nut abscission up to 15-fold within four weeks compared to untreated trees.

In cotton, ethephon serves a dual purpose – it acts as both a boll opener and a defoliant. By triggering leaf drop and encouraging boll split simultaneously, ethephon allows mechanical harvesters to collect cotton more cleanly, improving lint quality and reducing the number of passes needed through the field.

However, abscission promotion is not without risks. High rates of ethephon can cause excessive leaf drop, which may weaken the tree and reduce the following year’s productivity. In some nut crops, aggressive ethephon treatment has been associated with reduced kernel weight and smaller nuts. This means growers must carefully calibrate concentrations and timing to maximise harvest efficiency without long-term harm to the crop.

Sprout suppression in stored potatoes 🔗

Ethylene has also found a niche in post-harvest potato storage. When applied at low concentrations in storage facilities, ethylene suppresses sprout development in potatoes, extending their marketable life. This application is particularly valuable for fresh-market potatoes, where sprouting renders the product unappealing to consumers. Ethylene-based sprout suppression offers a chemical-free alternative to traditional sprout inhibitors, and its residue-free nature makes it compatible with organic storage protocols in some regions.

Managing ethylene to avoid negative effects 🔗

While ethylene is a powerful and versatile tool, it is also potent at very low concentrations – even trace amounts can trigger physiological responses in sensitive crops. This creates a significant challenge in mixed-storage environments. If ethylene used to ripen bananas leaks into a space storing leafy greens, berries, or cut flowers, it can cause premature yellowing, wilting, softening, or spoilage in those products.

Effective ethylene management requires several strategies. Ethylene-sensitive produce must be stored separately from ethylene-producing or ethylene-treated crops. Adequate ventilation is essential to prevent gas buildup, and ethylene scrubbers – devices that adsorb or oxidise ethylene from the air – are increasingly used in modern cold-storage facilities. Additionally, compounds like 1-methylcyclopropene (1-MCP) can be applied to ethylene-sensitive produce to block ethylene receptors and delay unwanted ripening or senescence.

Understanding which crops are ethylene-sensitive and which are tolerant is essential knowledge for anyone involved in post-harvest logistics. Without this awareness, a well-intentioned ripening operation can inadvertently cause significant economic losses in adjacent storage areas.

A look ahead: sustainable ethylene use 🔗

Ethylene remains indispensable in agriculture, but its future use is likely to become more targeted and efficient. Researchers are developing improved catalytic generators that produce ethylene on-site from ethanol, reducing reliance on petroleum-derived gas cylinders. Precision-dosing technologies are also emerging, allowing facilities to apply exactly the right concentration for a specific crop batch, minimising waste and environmental emissions.

At the field level, the development of crop varieties with modified ethylene sensitivity – through both conventional breeding and gene-editing techniques – promises to give growers even more control over ripening, abscission, and shelf life. Combined with better storage infrastructure and real-time ethylene monitoring, these advances could significantly reduce post-harvest losses, which currently account for a substantial share of global food waste.

What do you think? Given ethylene’s dual role as both a beneficial tool and a potential cause of spoilage, how should the agriculture industry balance its widespread use with the need to protect ethylene-sensitive crops during storage and transport? And could plant breeding eventually reduce our dependence on external ethylene applications altogether?

References

1. https://extension.umd.edu/resource/ethylene-and-regulation-fruit-ripening
2. https://www.ams.usda.gov/sites/default/files/media/EthyleneCropsTechnicalReport2023.pdf
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC4767906/
4. https://www.valentbiosciences.com/blog/pincor-promotes-pineapple-production/
5. https://www.sacvalleyorchards.com/walnuts/ethephon-for-earlier-harvest/
6. https://www.sciencedirect.com/science/article/abs/pii/S030881462202725X
7. https://www.sciencedirect.com/science/article/abs/pii/S0925521411000974
8. https://pmc.ncbi.nlm.nih.gov/articles/PMC47584/
9. https://www.tandfonline.com/doi/full/10.1080/14620316.2024.2434614
10. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.968315/full