The colour of the table grape fruit is a very important appearance index, which is the result of the comprehensive action of various pigments.
As the fruit matures, the anthocyanin content in the peel gradually increases, while the chlorophyll content gradually decreases. When the fruit is ripe, the chlorophyll content of the peel has been reduced to the lowest level. The type and content of anthocyanin synthesis determine the degree of coloring of the grape fruit.
Anthocyanidins mainly exist in the epidermis of grape fruits. There are many types & high content anthocyanin in grape peel. They are the decisive factors that affect the colouring effect of grape fruit, directly affect the appearance of the table grape fruit, affect the product characteristics and consumers’ desire to buy, and then affect the price.
According to our many years of planting experience, there are mainly the following five factors that affect the colouring of grapes.
1. Lighting Conditions
The light intensity is closely related to the colouring of grape fruits. The fruit color during grape ripening stage is mainly determined by the content and type of anthocyanins. Light activates phytochromes, induces and increases the activity of enzymes in the anthocyanin synthesis pathway, promotes the accumulation of anthocyanins, and then affects fruit colouring.
When the light intensity is lower than 50% of full light, the anthocyanin content increases with the increase of light. Although the fruit can mature normally in an environment with no light at all, there is no accumulation of anthocyanins.
2. Vineyard Temperature
Temperature affects the colour of grape berries by affecting the stability and synthesis of anthocyanins. Low temperature conditions are conducive to the accumulation of anthocyanins. Under high temperature conditions, the synthesis of anthocyanins is inhibited and the degradation of anthocyanins is rapid. As the temperature increases, the half-life of anthocyanins decreases.
Larger temperature difference between day and night during fruit ripening is conducive to fruit colouring. The low temperature at night inhibits the respiration of leaves and fruits, which is conducive to the accumulation of sugar. Anthocyanins are formed on the basis of sugar metabolism and are converted from anthocyanins to anthocyanins. Sugar accumulation promotes the synthesis of anthocyanins and improves fruit color.
Nutrients are the indispensable foundation for the growth and development of table grapes. Grapes have different requirements for nutrients at different stages of development. A reasonable supply of nutrients is very important for fruit colouring.
The higher nitrogen in the soil will inhibit the biosynthesis and accumulation of anthocyanins. Excessive nitrogen will promote the conversion of sugars to amino acids and proteins. The sugar content in the fruit will decrease, which is not conducive to the accumulation of anthocyanins, and the chlorophyll content will increase. .
The appropriate amount of potassium in the soil helps to increase the anthocyanin content in the fruit. Potassium is an activator of a variety of enzymes, which can promote the transportation and accumulation of sugar in the fruit, thereby increasing the sugar content of the fruit, which is the synthesis of anthocyanins. Provide the necessary material basis.
Moisture affects the content and stability of anthocyanins. If there is too much rainfall during the fruit ripening period, the skin cells will have too much water content, thereby reducing the concentration of sugar, acid and anthocyanins, so the fruit is poorly colored. Investigations show that grapes grown on dry soil have high sugar content and better colouration.
5. Plant Endogenous Hormones
Ethylene is an endogenous plant regulators that can promote the decomposition of chlorophyll, the formation of pigments, the conversion of organic acids and the formation of fruit aromas. Ethylene can increase the circulation and accumulation of sugar, and can directly regulate the physiological and biochemical processes of anthocyanidin synthesis and promote the synthesis of anthocyanins, thereby promoting fruit colouring.
ABA is also a key inducement of pigment formation. In the mature stage, the endogenous ABA content of grape fruits increases, which strongly promotes the synthesis of ethylene in the fruit, thereby promoting the synthesis and accumulation of fruit anthocyanins.
Similar to the mechanism of ABA, Prohydrojasmon can promote the synthesis of ethylene and esters in apple and grape fruits, thereby increasing the content of anthocyanins and carotene, promoting the degradation of chlorophyll, and improving the colour of the fruit.