Apple fruit colouring problems: thermoregulation of ethylene synthesis and correction with Foliart Iliostop
One of the key markers of marketable quality in apple fruit — particularly in red-skinned varieties — is the intensity and evenness of the anthocyanin blush. Colour development is a complex physiological and biochemical process, governed both by the variety’s genetics and by external environmental conditions. In orchard practice, it’s not uncommon for fruit to stay pale in years with an abnormally flat temperature regime — without pronounced day-night swings — failing to reach the colour typical of the variety. The cause of this lies in a disruption of the natural hormonal signal for ripening, in which ethylene plays the central role.
Ethylene and the temperature trigger for colouring
Ethylene (C₂H₄) is a gaseous phytohormone that serves as the master regulator of ripening and senescence in climacteric fruit, a category that includes apples. Under ethylene’s influence, genes encoding the enzymes involved in anthocyanin biosynthesis — the pigments responsible for red, pink and purple fruit colour — are switched on in the skin cells. At the same time, ethylene drives chlorophyll degradation, which lets the red pigment become visually dominant.
Endogenous ethylene synthesis in fruit tissue is a temperature-sensitive process. The key factor driving ethylene production isn’t so much the absolute temperature as the daily amplitude of temperature swings. Cool nights (in the 10–15°C range) combined with warm, sunny days (20–25°C) create the optimal thermal gradient, which the fruit reads as a signal to shift into active ripening. Under these conditions, the ethylene-biosynthesis enzymes — ACC synthase and ACC oxidase — become activated, and hormone concentration in the tissue starts rising exponentially.
Without a pronounced gap between day and night temperatures — for example, when nights stay warm, above 18–20°C, or days remain cool and overcast — the temperature trigger doesn’t fire. Ethylene production is delayed, or stays at an insufficient level. As a result, fruit that has already reached technical maturity in terms of sugar and starch content can remain green, or develop only a faint, patchy blush.
Foliart Iliostop as an inducer of ethylenogenesis and enhanced colouring
When the natural temperature signal for ethylene synthesis is absent or weak, the agronomist needs a tool to artificially trigger the process. Under the approach discussed here, Foliart Iliostop can serve as that tool.
Foliart Iliostop’s mode of action, in the context of enhancing apple colour, works through its ability to provoke endogenous ethylene production. Unlike direct application of synthetic ethylene producers (such as ethephon), which introduce the hormone from outside and can cause uncontrolled acceleration of ripening and premature fruit drop, Foliart Iliostop acts more physiologically. It creates specific metabolic conditions in plant tissue that cellular receptors interpret as a signal to launch the plant’s own ethylene cascade.
This stimulation triggers the natural processes that accompany ripening in the fruit:
Activation of anthocyanin biosynthesis in the hypodermal cells (the subsurface layer), producing an intense, even red colour.
Faster chlorophyll degradation, so the green background of the skin gives way to a yellowish or creamy tone, against which the red blush stands out with more contrast and appeal.
Synchronised ripening across the canopy, which helps produce fruit batches with more uniform marketable quality.
Practical application
For the best colour-enhancing effect, Foliart Iliostop should be applied in the phase leading up to natural ripening, or at the first signs of lagging skin colour development. The product is applied as a foliar spray, with a spray volume sufficient to fully wet the fruit surface and the leaf canopy.
It’s important to note that the treatment’s effectiveness depends directly on the tree’s overall physiological condition. Stimulating ethylenogenesis will only succeed if the plant has an adequate supply of mineral nutrients — above all potassium, magnesium and the micronutrients that act as cofactors for the anthocyanin-synthesis enzymes.
Conclusion
Poor apple colouring in years with an unfavourable temperature regime has a clear physiological explanation, rooted in a disruption of the natural thermoregulation of ethylene synthesis. Applying Foliart Iliostop, which can provoke endogenous ethylene production, is a technological approach that compensates for the missing natural temperature signal. This makes it possible to obtain fruit with intense, even skin colour and strong marketable characteristics even in seasons with abnormally flat temperatures.
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