What about the cracking fruit of Da Hongrong apple?

What about the cracking fruit of Da Hongrong apple?

On August 29, 2017, Hou Lao San of Taoyuan subdistrict office in Pingyuan County came to consult with four big Hongrong apples. It was found that the apple was badly cracked. According to the field investigation in the garden, the fruit cracking rate is 60% to 70%, and it is still increasing. 7 apples were split on individual fruiting branches and 6 apples were split. The fruit cracking performance of Dahongrong apple is different, including longitudinal crack (figure 1), transverse crack and transverse crack (figure 2). Transverse cracking usually occurs in the vertical middle of the fruit, with a depth of more than 1 cm, and the heavy fruit is nearly split (figure 3). The longitudinal fissures are mainly irregular cracks with different depths and red pigment deposits on the Yang fissure surface (figure 4). Fruit cracking occurs even in bagged fruit (Fig. 5) [Jishan Huayao].

Fig. 1 Longitudinal crack

Fig. 2 Longitudinal crack and transverse crack interlaced

Fig. 3 Longitudinal crack nearly split

Fig. 4 Longitudinal profile of dehiscence

Fig. 5 the bag also cracked the fruit

There are several kinds of discussion on the causes of fruit cracking: first, the theory of uncoordinated growth. We know that the fruit growth periods of different kinds of fruit trees are different, and the growth range of fruit volume is different among tree species, forming different growth curves. The enlargement pattern of apple belongs to S type, and the size of fruit depends on the number and size of cells. The fruit cell meristem belongs to the apical meristem without cambium. During the initial cell division, the fruit grows rapidly in the longitudinal axis, and the ratio of fruit longitudinal diameter to transverse diameter is larger. In the later stage, the transverse diameter exceeds the longitudinal diameter with the increase of cells. When the flesh expands faster than the peel, the fruit growth is unbalanced, and when the pulp volume expands beyond the peel expansion limit, the pericarp is broken. The second is the theory of improper water management. If the soil is dry in the early stage of fruit growth, the pericarp growth rate is slow, the internal cell space of the fruit is small, the cell density and fruit firmness increase, and when sudden rainfall or irrigation, the soil moisture increases sharply, and the root quickly absorbs a large amount of water and transports upward to the fruit. The pulp expands rapidly, and the pericarp can not withstand the expansion of the pulp and crack. The third is the theory of damage. The harmful parts of drugs, diseases and insect pests often cause the pericarp to stop growing, and the growing part is squeezed and torn apart, which becomes the starting point of fruit cracking. In addition, the fruit is exposed to the light surface, the temperature difference between day and night is large or the rain is easy to crack the fruit, the crack is often in the sunny part. Fruits with sunburn scars are easy to crack, crack along the sunburn point in case of rain, and then spread to other parts. Fourth, the theory of pressure. The higher the sugar content of the fruit, the greater the osmotic pressure, the easier it is to absorb water from the outside world. If the water is absorbed too quickly, the pulp will expand rapidly, break the pericarp and cause fruit cracking. The fifth is the theory of imbalance between nitrogen and calcium. Some studies have shown that when the nitrogen content is on the high side, it will affect the absorption of calcium. Calcium is a stable element in the structure of fruit cell membrane. When calcium is deficient, the cell structure is unstable and fruit cracking is easy to occur.

The traditional solutions to fruit cracking include water control method, calcium supplement method, bagging method, strengthening management method and so on. The cracking fruit seriously causes the fruit to be unsalable, unable to form a commodity, and loses its cultivation value. According to the survey, Dahongrong apples generally mature in the first ten days of September in the plain, and the early stage of fruit ripening is the local rainy season. It has been six years since Hou Lao San introduced Dahongrong apple in 2012. Calcium fertilizer was replenished year after year and bagged, but fruit cracking occurred year after year. This shows that the fruit cracking is caused by congenital soil and water disobedience of Dahong apple. Hou Lao San asked what to do next in orchard management. There is only one suggestion, that is to change varieties, implement high grafting, and graft varieties with good market prospects and uncracked fruit.