First, the color classification of apples
We often see the colors of apple fruits, mainly green, yellow and red. Among them, red apples can be divided into bright red, deep red and dark red according to hue, and can be divided into flake red and stripe red according to hue. The color of fruit mainly refers to red. For red varieties, high-quality and high-grade apples need bright red fruits. Full red means that the whole fruit surface, including the fruit stalk depression and calyx depression, is red and basically uniform. In order to make the apple color uniform, bright and full, we must first understand the coloring mechanism of apple fruit.
Second, the coloring mechanism of apple fruit
Chlorophyll, carotenoids and anthocyanins are the main pigments that determine the coloring condition of apple peel. Its colors are green, yellow and red. The proportion of the three pigments is different, which makes the fruit show different colors. During the development of apple fruit, all three pigments have their own dynamic formation rules. Among them, the formation of chlorophyll and carotenoid is mainly in the early stage of fruit growth and development, while the formation of anthocyanin starts from the gradual maturity of fruit, which is a sign that apple fruit begins to mature. Anthocyanins give fruit red, which is of great significance to the coloring and commodity value of apple fruit.
Apple peel color can be divided into surface color and background color. The background color of pericarp is determined by chlorophyll and carotenoids, which are green or yellow to varying degrees, and generally dark green when the fruit is immature; When the fruit begins to ripen, three things will happen. First, the green color does not fade at all, and the background color is different degrees of green; Second, the green fading is not complete, and the background color turns to green yellow or yellow-green; Third, the green gradually fades until it fades completely, and the background color also turns yellow to varying degrees, from yellowish white, milky yellow to dark yellow. The surface color of pericarp is determined by anthocyanins. When the fruit matures, it usually shows red, green and Huang San species, and there are other colors, but they are rare.
For red varieties, the color of pericarp is determined by background color and surface color * * * (first determined by background color). When the background color is close to white, it can form a very bright red; When the background color is dark green, it will form dark brown. In the early stage of apple fruit expansion, chlorophyll and carotenoids were mainly formed in the peel, so the young fruit also showed corresponding green color. As the fruit entered the mature stage, a large number of anthocyanins were formed in the peel, and the color of the fruit gradually changed from green to red with the increase of anthocyanins in the peel.
Anthocyanin is the result of the combination of anthocyanin, carbohydrate and light. Among these factors, light plays an important role in the formation of anthocyanins. In practical cultivation, the fruit with good light outside the crown of the same fruit tree is better colored, while the fruit with good light inside the crown is relatively poor, which also confirms this point.
After the above interpretation, we understand the coloring mechanism of apple fruit. In the coloring of apples, the amount of anthocyanins plays a decisive role in the color of apples, and light is an important factor to determine the formation of anthocyanins. Therefore, in order to make apples well colored and bright in color, the formation of excessive chlorophyll should be suppressed in the young fruit stage and the expansion stage, and good lighting conditions are necessary for the formation of anthocyanins in the expansion stage of apples.
Thirdly, measures to improve fruit coloring by controlling light conditions.
By understanding the mechanism of apple coloring, we know the importance of light to apple coloring. Therefore, in practical cultivation, we should promote apple fruit coloring by managing light conditions.
1. Bagging inhibits the formation of chlorophyll
As we mentioned earlier, the best shading method is bagging, which can be completely sealed and prevent erosion, killing two birds with one stone. And the bagging fruit has very strong coloring ability. In the early stage of apple fruit expansion, the better the shading effect of bagging, the better the inhibition effect on chlorophyll formation. In this way, the better the effect of promoting coloring after picking bags.
In actual cultivation, fruit bags should be selected according to different varieties and the difficulty of coloring. For varieties that are easy to be colored, black single-layer paper bags should be selected; For varieties that are not easy to color, double paper bags should be selected.
In addition, in addition to choosing different paper bag types for different varieties, bagging time also plays a vital role in the coloring of apple fruit. Choosing suitable bagging time is beneficial to promote fruit coloring. Yellow-green apples, such as Marshal Huang and bananas, generally begin bagging 12 days after flowering; Red early-maturing varieties such as Gala and Jonakin are generally bagged about 25 days after flowering; Red late-maturing varieties, such as Red Fuji and Jiangjun, generally start bagging 30 days after flowering.
Early bagging has a good effect on inhibiting chlorophyll formation, but it is not conducive to fruit expansion, and it is easy to form fruit drop in hot and dry weather. Too much bagging will make the fruit fade incompletely and fail to achieve good coloring effect. Bagging can be carried out in the morning when the dew is dry and in the evening on sunny days, but in order to avoid fruit wilting caused by too strong sunlight at noon, bagging can be carried out at 8: 30 am ~11:30 and 2: 30 pm ~ 5: 30 pm, and bagging can be carried out all day on cloudy days, but it is not suitable for rainy days.
2. Promote the formation of anthocyanins by picking bags.
The growth and development of bagged fruit under shading environment can inhibit the formation of chlorophyll, promote the background color of peel to be close to white, and lay a solid foundation for the color change of fruit in the later stage. After the apple fruit enters the mature stage, picking the bags in time and allowing the fruit to receive sufficient light can greatly promote the formation and accumulation of anthocyanins and create favorable conditions for the peel to turn red.
The choice of picking time will also affect the coloring effect of fruit. Picking the bag too early will make the gloss of the fruit surface worse; If the bag is picked too late, the background color of red fruit will turn green, the surface will turn yellow, the color will slow down and the flavor will fade, which will affect the quality of apple.
Different apple varieties, different climatic and environmental conditions, and different bag picking time. Red varieties with fast coloring, such as New Red Star and New Jonah Gold, are generally suitable for picking bags 5-20 days before harvesting. In cold apple producing areas with large temperature difference, the bags can be picked 10- 15 days before harvesting. In apple producing areas with high altitude and strong sunshine, bags can be picked 7- 10 days before harvesting, which can effectively avoid fruit coloring. For varieties that are difficult to color, such as Red Fuji and Jonakin, bags should be picked about 30 days before picking. In cold or large temperature difference apple producing areas, bags should be picked in advance, preferably 20~25 days before picking.
When carrying a bag, the crown should be inside first, and then outside; Pick dense trees first, and then pick light trees. Choose the middle and low-grade bag first, and then choose the high-grade bag. If it is a double bag, tear off the outer bag first, and then remove the inner bag after 3~5 days; The bottom of the single-layer bag can be opened now or the paper bag can be torn into strips longitudinally, and it can be removed after 3~5 days to prevent sudden sunburn. When picking bags, you can pick bags after 10 am, when the surface temperature of the fruit is close to or slightly higher than the atmospheric temperature, and it is not advisable to pick bags in the morning or evening.
3. Improve lighting conditions by pruning in autumn.
Good lighting conditions are the premise and guarantee to improve fruit coloring. It has a direct effect on fruit coloring. In order to ensure a good light environment for fruit after bagging, autumn pruning is usually carried out 3~5 days before bagging or after bagging, so that the fruit can get sufficient light. To achieve this goal, firstly, we should moderately remove or retract the over-dense branches, over-flourishing branches, overlapping branches, peripheral competing branches and upright flourishing branches on the main branches in the crown, so as to improve the light inside the crown and the light transmittance of trees. For the fruit branches drooping due to gravity, measures such as pulling branches can be taken to improve the overall lighting conditions. What needs to be reminded here is that the pruning amount in autumn should not be too large, so as not to affect the tree potential.
4. Artificial leaf picking and fruit transfer further promote coloring.
By pruning in autumn, the light environment of fruit is greatly improved. However, in actual production, apple fruit is often blocked by branches, leaves or fruits, resulting in green-spotted fruit and semi-red fruit. In order to avoid this phenomenon, manual leaf picking and fruit turning before harvesting has become an essential technical link to promote full coloring of fruits.
(1) picking leaves
Leaf picking is to remove the leaves that affect the illumination of apple fruit, so as to increase the light transmittance of the whole tree, eliminate the green patches on the surface of the fruit and promote the uniform coloring of the fruit. Mastering the time, method and quantity of picking leaves can not only affect the nutrient accumulation of trees, but also promote the coloring of fruits.
The leaf picking period should be determined according to the biological characteristics of different apple varieties, generally starting from 3 to 5 days after bagging. The fruit development period of middle-mature varieties such as Gala is short, and leaves can be picked about 15 days before harvesting; Marshal Xin Hongxing and others are short-branched apple varieties, which are easy to be colored, and the leaves can be picked later, and the suitable time is 15~ 20 days before harvesting; Late-maturing varieties such as Red Fuji should start picking leaves 20~25 days before harvesting.
In order not to affect the nutrient accumulation of apple trees in the late growth stage, leaves are usually picked twice before harvesting. Each removal object and intensity are also different. The object of picking leaves for the first time is the leaves close to the fruit, and the shaded leaves within 5 cm from the fruit, including the old leaves and leaflets with low yellow thickness, should not be too large this time, otherwise it will easily cause physiological diseases such as fruit sunburn. The second leaf picking is to solve the overall illumination of the tree. It is usually necessary to remove some leaves from the new buds around the fruit. Remove the leaves around the fruit in the range of 10 ~ 20cm. Don't pick the leaves too early at this time, usually 5~ 15 days before harvesting.
Pay attention to the following points when picking leaves: First, grasp the time of picking leaves. The organic nutrition of trees is produced by photosynthesis of leaves. Picking leaves too early will reduce the synthesis of organic matter, and then affect the formation of anthocyanins, which is not conducive to color changes. After picking leaves too late, the fading time of green spots is not enough, which affects the appearance and quality of fruits. Second, when picking leaves, it is best to cut the leaves short from the petiole with scissors and keep the petiole, so as to avoid damaging the teeth of the branches and losing water. Third, the action should be light when picking leaves, so as not to use too much force to cause the branches to shake and the fruits to fall off.
(2) Turn over the fruit
Turning the fruit is a way to make the fruit completely colored. The method is very simple. Turn the direction of the fruit artificially, change its light receiving surface, and eliminate the difference between Yin and Yang. Usually, fruits are only turned over once in production.
Generally, the fruit transfer time is 8~ 10 sunny day after picking bags. When the sunny side of the fruit is completely colored, showing the color of the variety and meeting the requirements of commodity standards, the fruit can be transferred. Fruit turning should be carried out after 4 pm on sunny or cloudy days to prevent the uncolored fruit surface from being sunburned due to its inadaptability to strong light and local high temperature. The method of turning the fruit is to hold the fruit branch with one hand, and gently drag the bottom of the fruit branch with the other hand, so that the fruit branch faces in one direction and gently rotates 150~ 180 degrees, so that the original reverse side turns to the front side to receive light, fixing the position of the fruit branch and preventing the fruit branch from naturally returning to its original position. When turning the fruit, always turn it in the same direction, and don't twist it left and right or use too much force, so as not to twist the fruit handle and cause the fruit to fall off. For fruits that are not suitable for fixation after fruit transfer, narrow transparent tape can be connected to suitable branches nearby for fixation to prevent the fruits from rotating.
5. Enhance lighting by laying reflective film.
Generally speaking, the fruits in the upper part of the crown are easier to be colored than those in the middle and lower parts, because the light conditions in the upper part are stronger than those in the middle and lower parts. In order to change this phenomenon, we take the technical measures of laying a reflective film under the tree to reflect sunlight to the fruit from bottom to top, so as to improve the light intensity of the fruit in the middle and lower part of the crown and all the fruits with depressed calyx, so that the fruit can receive enough light and be fully colored, thus improving the rate of full red fruit.
At present, silver reflective plastic film is widely used in apple production. Silver reflective film is a thin flat film, and its reflectivity is as high as 8 1.5%~9 1.5%, which can effectively enhance the canopy illumination and increase the proportion of ultraviolet rays. The cost of the membrane is low, and it can generally last for three years.
The laying time of reflective film is generally controlled after autumn shearing and picking the first leaf, and completed before harvesting 10~25 days. The film is laid too early, and the trimmed branches and leaves fall on the reflective film, which affects the reflective effect; Too late paving will shorten the exposure time of the fruit to reflected light, and the coloring effect cannot be achieved. The film spreading range is mainly based on the whole projection plane of the crown, and the edge is flush with the outer edge of the crown. High-density dwarf apple orchards, with small row spacing, usually lay reflective films between trunks to reflect light to the whole orchard ground; For medium-density dwarf apple orchards, the row spacing is large, and the forward film laying method under the crown is usually adopted, that is, a row of reflective films are laid on both sides of the crown projection of apple trees to form a reflection area centered on the crown projection; Apple trees with large crown and open heart are usually covered with plastic film around the projection area around the crown.
Before laying the film, clear the weeds and gravel clods under the canopy and level the ground. When laying the film, put the rolled reflective film at one end of the orchard, and then slowly roll the film back. When paving, use stones, clods or ropes to press the edge of the film to prevent the reflective film from being blown apart by the wind. After sticking the film, it is necessary to clean the leaves, dust and other sundries on the surface of the film regularly, and level the blown film again in time to avoid affecting the reflective effect.
6, timely harvesting
After careful coloring management, the fruit gradually showed the unique red color of this variety, and the color became more and more bright, indicating that the fruit had entered the harvest period. As we all know, the fruit on the same tree has different coloring degree and maturity because of its different position, branch type and light intensity. In order to ensure that apple trees are full of red fruits, high quality and high yield, they must be harvested in stages at the right time and in batches when they are ripe.
Under the condition of bagging cultivation, the fruit is colored and ripened neatly, and it usually needs to be picked 2~3 times. The colored fruits around the upper part of the crown are harvested for the first time, and the remaining fruits are harvested for the second or third time after coloring. In the suitable harvest period of apples, you should pick them as late as possible. The later the harvest, the better the fruit coloring and quality. Because the skin of bagged fruit is thin and tender, it should be handled with care in the process of harvesting and handling, so as to avoid touching, pressing, stabbing and scratching, and reduce the commodity value of apples.
Apple coloring is a complicated process. In addition to light, there are many factors that affect apple coloring. While doing well the management measures we introduced above, we should also strengthen the management of water and fertilizer in orchard, fruit tree pruning and pest control to ensure the production of apples with excellent appearance and internal quality and achieve good economic benefits.