The action is mainly based on mitigating or minimising the effects of high temperatures on the denaturation of anthocyanins. In this way they exert a series of beneficial actions:
→ increase the osmotic potential of the cell. Maintaining its hydric rate in high temperature conditions. Avoiding enzymatic and thermal destruction of anthocyanins.
→ as heat stress is reduced, the photosynthetic rate does not slow down. As a result, the plant does not reduce sugar production.
→ help to raise the concentration of sugars in the cell: by stimulating the activity of the PAL (phenylalanine ammonium lyase) enzyme involved in anthocyanin synthesis.
→ inhibit the greening action of gibberellins.
→ Improve the general condition of the plant.
→ Increases the vigour and strength of the plant. This results in higher crop yields and crop quality.
→ Their use reduces the use of chemical plant protection products. This facilitates better marketing of residue-free production and, consequently, higher profitability.
→ They are natural, non-toxic substances that do not leave residues. They are fully biodegradable and do not affect auxiliary fauna.
Pome fruit trees, especially in red Red Delicious and bicoloured apple varieties (Fuji, Gala, Annurca…).
Make one foliar spray application at the beginning of veraison and another after 15 days:
→ when the daytime temperature is between 20 – 32 ºC. Apply a dose of 250 grams per 100 litres of water (2.5 kg per Ha).
→ when the daytime temperature is higher than 32 ºC. Apply a dose of 300 grams per 100 litres of water (3 kg per Ha).
The appearance of colour is associated with the ripening of the fruit. The chloroplasts of the fruit cells undergo a ‘dismantling’, which destroys the chlorophylls. This phenomenon unmasks other existing pigments, such as carotenoids (β-carotene, lycopene). In addition, ripening involves the de novo synthesis of flavonoid-like pigments located in the vacuole, the most abundant of which are anthocyanins or anthocyanins.
Anthocyanins are synthesised via the phenylpropanoid pathway, whose precursor is phenylalanine. The first enzyme to act in this pathway on this precursor is phenylalanine ammonium-lyase (PAL). This pathway is regulated at the genetic level and is highly influenced by abiotic factors, such as temperature and light or ultraviolet radiation, osmotic stress, as well as the hormonal level (gibberellins) or by mineral elements such as inorganic nitrogen.
Anthocyanins are stabilised by glycosylation, in union with sugars, and by the action of the enzyme UDP-glucose-flavonoid 3-0-glucosyltransferase, a phase that begins at veraison (start of colour change) and accumulates in the vacuoles of the epidermal cells during the ripening of the fruit. The sugar in the anthocyanin molecule makes them soluble and stable.
The type and number of sugars bound to the aglycone molecule, the position of this bond and other factors play an important role in the colour and stability of the anthocyanins. Another stabilising factor is co-pigmentation, which is the acetylation of the sugars with colourless flavoniods.
Anthocyanins accumulate to protect the tissue from photo-stress when too much radiant energy is absorbed and cannot be used; therefore, low light levels and high temperatures do not provoke this type of stress, so anthocyanin synthesis does not take place.
High, but not excessive, temperatures are necessary for an adequate photosynthetic rate, an optimal development of the fruit and a correct ripening. However, temperatures above 32 °C cause a degradation of anthocyanins.
In hot weather, the photosynthetic activity of the leaves during the day decreases sharply and during the night the carbohydrates are rapidly used for respiration, which is more intense the higher the temperature, leaving little or none available for pigment synthesis.
The presence of sugars is essential for the formation of anthocyanins. Fruits better exposed to light but with low sugar content do not colour well.
Low temperatures contribute to colour formation by directly reducing the activity of gibberellins, which increases the activity of the PAL enzyme and therefore the synthesis of anthocyanins.
Temperature fluctuations between day and night, accompanied by cool night-time temperatures (10-15ºC), in the period prior to harvesting, are the optimum conditions for good colouring, given that anthocyanin synthesis increases.
The decrease in temperature, as well as influencing the development of the fruit, helps the synthesis of anthocyanins, because the photosynthetic activity is activated, producing a greater quantity of carbohydrates, which will be used for the synthesis of anthocyanins.
Certain sugar limits in the cell induce genes involved in anthocyanin synthesis, while gibberellins inhibit these effects.
Location: Lérida (Spain), 2015.
Two foliar applications of cromar were made at a dose of 3 g/lt, the first one at the beginning of the colour change and the second one after 15 days.
The number of fruits was measured in relation to the percentage of coloured surface area 30 days after the first application. The cromar treatment showed 25 % more fruits with a coloured surface between 75 and 100 % than the control.
The intensity of the skin colouring was also measured, reaching the conclusion that the treatment with cromar biostimulant showed a higher percentage of fruit with a bright red shade, an increase of 44% with respect to the control.
Location: Ferrara (Italy), 2015.
Two foliar applications of cromar biostimulant were made at a dose of 2.5 g/lt, the first one at the beginning of the colour change and the second one after 15 days.
The percentage of coloured skin surface of 100 fruits was measured at the time of harvest. In the sunny area, 30 % more coloured surface area was obtained than the control, and in the shaded area, 44 % more colour was obtained than the control.
% surface area of coloured skin (fruits of first harvest)
% surface area of coloured skin (second harvest fruits)