Causes of fruit cracking of sweet cherry and its preventive measures

Causes of fruit cracking of sweet cherry and its preventive measures

1 influencing factors of fruit cracking

1.1 the relationship between genetic characteristics of varieties and fruit cracking of sweet cherry it is generally believed that there is a certain correlation between sweet cherry fruit cracking and its own variety characteristics, the fruit cracking sensitivity of sweet cherry is determined by genetic characteristics, and the degree of fruit cracking is significantly different among varieties. the fruit cracking sensitivity of different rootstocks of the same variety is also different, and the fruit cracking characters of parents can have an effect on the offspring through inheritance. Yamaguchi et al investigated the fruit cracking ability of 37 sweet cherry varieties, and found that there were significant differences in fruit cracking among varieties, which was positively correlated with fruit quality and pulp firmness. Greco et al. [Jishan Huayao] studied the cracking resistance of 30 sweet cherry varieties in Appley, Italy. The results showed that the fruit cracking sensitivity of sweet cherry was related to genotypes. Simon analyzed the fruit cracking sensitivity of sweet cherry varieties, and divided the fruit cracking resistance of 51 main sweet cherry varieties in the world into five grades: extremely resistant to cracking, easy to crack, easy to crack and very easy to crack, among which the most resistant varieties were "Star" and "Sue", and the resistant varieties were "Lapins" and "Sam". "Summit", "Sunburst" and "Sylvia" are more resistant to cracking, while "Santina", "Stella", "Van" and "Sweetheart" are more susceptible to cracking. Extremely easy to crack fruit varieties are "Bing", "Tieton" and so on. The fruit cracking resistance of some varieties in Hungary is slightly different from that in China, which shows that the fruit cracking sensitivity of the same variety is also different in different cultivation areas. Balbont í n et al used sweet cherry varieties with different cracking resistance as test materials, and found that expansin gene was highly expressed in the ripening stage of crack-resistant fruit, and expansin gene could relax the pericarp cell wall and release the cell wall tension quickly, so as to avoid sweet cherry fruit cracking. Other studies have shown that there is a great correlation between fruit cracking and the characteristics of epidermal cells at the top of the fruit. The varieties with short epidermal cells at the top of the fruit have a lighter degree of cracking, while the varieties with longer epidermal cells at the top have serious fruit cracking. The varieties with thick pericarp and neat cell arrangement are not easy to crack, while the varieties with thin pericarp, large cell space and loose cell arrangement are easy to crack fruit. Fruit cracking is related to the poor expansibility of pericarp and the increase of pulp osmotic pressure during fruit ripening.

1.2 effect of external environment on fruit cracking of sweet cherry

Water is the main environmental factor affecting fruit cracking, whether attached to the fruit surface or soil moisture, is an important factor to induce sweet cherry fruit cracking. The varieties that avoid the rainy season in the mature period are not easy to crack, and the varieties that encounter continuous rainfall or torrential rain during the mature period are easy to crack. Some studies have concluded that fruit cracking is caused by Rain Water directly attached to the fruit surface, osmotic absorption is the driving force of water movement, and it is also considered that the water absorbed by fruit tissue from the fruit surface is not the main factor affecting fruit cracking. Studies such as Knoche showed that when the external humidity ≥ 75%, the incidence of sweet cherry fruit cracking increased; when the external humidity reached 100%, the incidence of fruit cracking was consistent with the incidence of pericarp immersed in water. The low-lying orchard is easy to accumulate water and the heavy soil viscosity is easy to cause fruit cracking. Fruit cracking can also be caused by a sharp increase in soil water content caused by "dry and wet" soil, or excessive irrigation before harvest. Temperature is another important factor affecting sweet cherry fruit cracking. When the external temperature is between 10 ℃ and 40 ℃, the sensitivity of sweet cherry fruit cracking increases with the increase of temperature. The sunburn part of the pericarp caused by strong light is often the starting point of fruit cracking. In addition, poor soil fertility or unbalanced fertilization will reduce the fruit cracking resistance of trees and cause fruit cracking. Many studies have confirmed that fruit cracking rate and fruit cracking index are significantly negatively correlated with calcium content in fruit, and spraying calcium compounds can reduce pre-harvest fruit cracking of sweet cherry.

(2) preventive measures for fruit cracking

Agricultural measures: when selecting sweet cherry varieties, we should not only consider the ecological conditions of the planting land, but also try to select anti-cracking fruit varieties. Relatively speaking, varieties such as "Rainier", "Rabins", "Pioneer", "Samitt" and "onyx" have lighter fruit cracking. To keep the soil moisture content relatively stable, irrigation should be small and repeated, especially in the fruit ripening period, do not "dry and wet". For orchards with poor drainage performance, pay attention to timely drainage and waterlogging prevention. Keep the soil loose, so that the root system is well ventilated, where there are conditions, legume straw can be deeply mixed to improve the soil. Avoid stagnant water for a long time and affect the normal physiological function of the tree. Physical measures: the physical method to prevent sweet cherry fruit cracking is to set up a rain barrier, which can build a simple plastic film to cover the rain before coloring the fruit, unfold the plastic film when it rains, and fold it up after rain. Chemical measures: increasing the application of organic fertilizer, increasing the content of organic matter in orchard soil and strengthening the potential of sweet cherry trees can improve their fruit cracking resistance. Sweet cherry after fruit setting to before harvest, spray 0.2% calcium chloride or "Guoshen brand" boron calcium treasure 0.25% solution, spray once every 10 days, spray 3 times in a row, can effectively prevent fruit cracking.