Study on the effects of different treatments on the cracked fruit of Ganping
Huang Meiling et al
Fruit cracking is the reaction of the fruit to its own internal growth and the external environment, which is a common physiological disease in the production of fruit trees. Fruit cracking will seriously affect the appearance quality and commodity value of the fruit. There are many factors that affect fruit cracking, and it is of great significance to understand the causes of citrus fruit cracking to prevent fruit cracking and reduce the prerequisites for fruit cracking, so as to improve the yield and quality of citrus fruits. "Ganping" is a potential variety of mid-to-late maturing mixed citrus, with excellent commerciality, strong tree strength, huge fruit shape, thin clothing bag, unique flavor and storage resistance. Jingyan County is known as the "hometown of citrus", and is also one of the counties with high-quality citrus commodity production bases in the country, with a long history of citrus planting. The county has built a citrus research institute, a commercialization processing center, and a good breeding base, relying on the citrus leading 100-mile industrial loop, and introducing and planting citrus varieties such as "Ganping", "Chunjian", "Shiranui" and so on. Jingyan County is one of the top 30 citrus counties in China, Jiyi Township of Jingyan County is a strong industrial town of the Ministry of Agriculture, Jiyi Late-maturing Citrus Provincial Modern Agricultural Park of Jingyan County is a 3-star Provincial Modern Agricultural Park, and Jiyi Town of Jingyan County is a citrus characteristic town. In addition, Jingyan County has created a tourist attraction with rural characteristics around the citrus township.
1 Materials and methods
1.1 Survey regional overview
Jingyan County is located in Leshan City, Sichuan Province, southwest of Sichuan Basin, located at 102°55'E ~104°00'E, 28°25'N ~29°55'N, is a typical hilly landform, located in the southwest of Sichuan Basin. The annual average temperature is 17.2°C, and the annual average sunshine hours are 1134.6h, the average annual precipitation is 1025.8mm, the frost-free period is 334d throughout the year, and it belongs to the humid climate zone of the central subtropics. It is the most suitable area for hybrid citrus cultivation in China's citrus ecological regional planning, with no frost damage in winter, no heat in summer, rich in soil minerals, purple-red sandy loam rich in calcium and potassium, and no heavy metal pollution.
1. 2 Test materials
The test material for the survey was a citrus orchard, and the variety was "Ganping". The orchard is located in Miaozishan Village, Jingyan County, at 29°46'N, 103°55'E. The park was established in 2016. "Ganping" is a new hybrid citrus variety newly introduced to the mainland, the male parent is Ponkan, the female parent is Nishinoka (Kiyomi × Trovita sweet orange), with a high sugar content, easy to crack fruit, the average fruit cracking rate can reach 60%. Due to the serious cracking of the fruit in the orchard "Ganping", the situation was followed up and investigated.
1. 3 Test Methods
Through field investigation, a follow-up questionnaire on the cracked fruit of "Ganping" was formulated, and three treatments were set up, which were in the shed, broken roots and no K fertilizer was applied. On August 18, 2022, the listing observation officially began, and field observations were carried out every 1 week, and the fruit cracking data were recorded on September 2, September 9, September 16, September 23, and September 30 of the same year, and the fruit cracking rate, fruit cracking time, fruit cracking method, etc., were compared, and the fruit cracking rate of different treatments was calculated.
1.4 Data Processing and Analysis
Excel was used for statistical analysis. Fruit cracking rate survey: the total fruit setting amount (M) and the total fruit setting amount (N) at the end of fruit cracking (October) of each tree after fruit setting were counted, and the difference between the two was the total number of fruit cracking, that is, fruit cracking rate = (M - N) /M ×100.
2 Results and Analysis
2. 1 Fruit splitting
The results of the survey showed that the time of fruit cracking was from mid-August to early October, with early and mid-September as the peak period for fruit cracking. The root breaking treatment had 40 fruit cracks, followed by 33 without potassium and 13 of the lightest early rain shelters in the shed (Table 1). Longitudinal fissures were the main method of fruit splitting, and the lumbar fissure gradually disappeared with time (see Table 2). It is speculated that the cause of the longitudinal fissure is the tearing of the peel when the fruit expands laterally. Lumbar cleft is a tear in the peel caused by the longitudinal elongation of the fruit. The results indicated that the fruit cracked lightly in the early stage of lengthening and growth, and when it entered the transverse expansion in the later stage, the fruit cracking began to be severe.
Table 1 Follow-up investigation of Ganping fruit cracking
Table 2 Statistics on fruit splitting methods
2. 2 Causes of fruit splitting
2.2. 1 Different varieties have different degrees of fruit cracking Fruit cracking is an important physiological disease in citrus production, which seriously affects the yield and reduces the economic benefits of fruit farmers, which is mainly determined by the genetic characteristics of the variety itself. Different citrus tree species (citrus, oranges, oranges, lemons, pomelo) or different varieties (different citrus varieties) have different degrees of fruit splitting. In general, citrus fruits are more likely to crack than oranges, and wide-skinned citrus fruits are lighter. Oranges, pomelos, and kumquat all have heavier fruit splits, while lemons rarely have fruit cracking. Since citrus is a natural or artificial hybrid offspring of tangerine-to-mandarin, tangerine and orange, mandarin and pomelo, the degree of fruit cracking of varieties is not only related to parental heredity, but also related to the tightness, thickness and skin uniformity of their own peels. In addition, citrus fruits are mostly oval-shaped, with a small distance from the waist to the top, rapid changes in peel thickness, and a relatively small fruit shape index, which is also easy to cause fruit cracking, while oblong fruits are not easy to crack fruit. The early-maturing Wenzhou mandarin orange is the most serious because of its thin peel and water foot cracking. "Ganping" has thin skin, sufficient moisture, full fruit, and is very prone to cracking fruit in the open field cultivation conditions in Sichuan.
2.2. 2 Cultivation practices affect fruit cracking Proper management practices allow citrus to maintain a balance between vegetative and reproductive growth without being prone to fruit splitting. Citrus orchard management involves pruning, flower and fruit thinning, fertilization, bagging, insect control, etc. If the tree is deficient in nutrients such as calcium and boron, citrus cracks will occur because the toughness of the peel is insufficient; If nitrogen fertilizer is used too much, the fruit will absorb too much fertilizer and water during the peak period of expansion, and it is easy to crack a large number of fruits; After high temperature and drought, too much water at one time will cause the citrus pulp to grow faster than the peel, and the peel will crack.
2.2. 3 Climatic factors Weather is an important factor in the fruit cracking of citrus. Temperatures fluctuate, and there is constant rain during the fruit expansion period, and there are often rainy and sunny weather, all of which can lead to fruit cracking. The development of citrus peel is directly affected by drastic temperature changes, which leads to inconsistent growth rates between pericarp cells and pulp cells, resulting in inconsistent growth rates of citrus peels and pulp cells. The cell division of citrus peel is inhibited by hot and dry weather and strong sunlight, the cell elasticity is weakened, and the peel stops growing early, resulting in fruit splitting. If the rain is too long, the citrus fruit is more likely to crack. During the fruit expansion period, in case of heavy rain, the growth rate of the peel is inconsistent with the growth rate of the pulp cells while causing fruit cracking. Prolonged drought and rainfall, frequent rain and drought climate, increase cell distension and lead to fruit cracking. Whether citrus fruit is cracked or not is also related to the physiological characteristics of the variety itself.
2.2.4 Other factors Other factors Other factors that affect fruit cracking are also the topography of the orchard, which is generally mild in mountain citrus orchards because the soil is highly resistant to drought. Exogenous hormones also have an impact on citrus fruit cracking, in the citrus fruit stage, in the citrus fruit stage, the use of "920" and other hormones for fruit preservation, the fruit cracking will be significantly reduced. This may be due to the fact that hormones cause the pericarp cells to divide more quickly, which increases the ability to resist stress.
Citrus fruit cracking often occurs at veraison or swelling stage. In the fruit expansion stage, the differentiation of various tissues in the fruit is inconsistent, the lignification degree of some cells is aggravated, and the local growth makes the growth of various tissues of the fruit uncoordinated, resulting in fruit cracking. Citrus assimilates gradually accumulate in the pulp as they are near-ripe, resulting in an increase in the pulp's ability to absorb water, and fruit cracking occurs when the pulp's pressure changes more than the extensibility of the peel.
3 Precautionary measures
3. 1 Breeding new varieties suitable for the right place Reasonable selection of rootstocks
The altitude, light and rainfall in different regions are different, according to the local climate, new varieties with different maturity stages and different stress resistance are selected and bred, so that the critical period of citrus fruit development can avoid bad weather such as high temperature, drought and rainy season. The rootstock mainly affected the potential, stress resistance and fruit quality of citrus trees, and different rootstocks had different effects on the supply of nutrients to the tree. When purchasing seedlings, it is necessary to choose the appropriate rootstock variety according to the demand. The citrus of citrus of citrus anvil is stronger alkali resistance and abundant yield than citrus aurantium anvil, earlier than red orange anvil, dwarfing, lush root system, many fibrous root groups, good fruit quality, strong stress resistance, and is a suitable rootstock variety for alkaline purple stone millet soil area in Sichuan and other places. Yulik lemon and Kiyomi orange orange have strong crack resistance, and there is no cracking phenomenon after high temperature and long-term drought and rainfall.
3. 2 Maintain a balanced water supply to the orchard
The new citrus orchard should choose the sandy loam soil with deep soil layer and high fertility, and the soil management should be strengthened for the existing orchard, and the soil permeability and water and fertilizer retention capacity should be increased through deep soil ploughing, so as to avoid drastic changes in soil moisture content and reduce the degree of citrus fruit cracking. In the management, orchard drainage and irrigation facilities should be done, and ridge cultivation and mulching should be adopted to balance soil moisture. The selection of "Ganping" orchard should be based on pH 5. 5 ~ 6. 5. Sandy loam soil with a depth of more than 80cm and a groundwater table of 80cm or less is appropriate. If a new reservoir is necessary for plots with insufficient water sources, attention needs to be paid to balanced water management to avoid water fluctuations in the rhizosphere environment. If it does not rain within 72 hours, the whole park will be sprayed with water once before 8:00 or after 20:00, and it is advisable to have runoff on the surface.
3. 3 Mineral elements
Fruit splitting is a physiological disorder reaction of the fruit, and citrus fruit cracking can also produce fruit cracking due to the lack and excess of mineral elements, which is a physiological disorder reaction of citrus fruit. The mineral elements in the peel are changed to a certain extent, which changes the structure of the peel or the activity of enzymes. Potassium is an indispensable mineral element for cell division, growth and cell wall formation in fruits, which can maintain high permeability of pulp cells. The supply of potassium can thicken the cell wall of citrus fruits, and the stress resistance of the tree will also be improved. Calcium is an important component that makes up the cell wall, participates in the formation of the peel, and increases the strength of the peel. Calcium is also involved in the composition of the cell membrane, the composition of the cell wall. Boron is also an important element in the synthesis of cell walls, and a lack of boron can lead to a decrease in yield, as well as a decrease in fruit quality. Nitrogen is beneficial to erythrin synthesis, can promote the growth and coordination of citrus fruit tissue, and reduce the occurrence of fruit cracking. The "Ganping" orchard can be sprayed with 0.5% potassium dihydrogen phosphate once in the whole garden when the flowers are gone, and then sprayed once after 7 ~10 days (this time the effect is mainly cell division, which promotes the increase in the number of pericarp cells). In mid-July and early August, spray potassium and calcium-containing foliar fertilizer once each (this time the effect on anti-cracking fruit is mainly to increase the toughness of peel cells). Increasing calcium fertilizer and reducing nitrogen, phosphorus and potassium at the fruit expansion stage can effectively reduce the occurrence of fruit cracking.
3. 4 Strengthen orchard management and increase peel crack resistance
Strengthen integrated orchard management. Pay attention to reasonable pruning, timely thinning of flowers, fruits, and branches, and reasonable stay, and the use of rain-sheltered cultivation in conditional orchards can effectively reduce the occurrence of citrus fruit cracking and diseases. Before the arrival of the summer dry season, loosen the soil and cover it with straw and green manure, which can keep the soil moisture content relatively stable and reduce fruit cracking. For weakened trees, it is necessary to pay attention to the recovery of tree potential, and reduce the amount of flowers and fruits through pruning. The spring shoots of young trees and weak trees should be removed from the weak and the strong should be retained, and the dense spring shoot group should be eliminated, and the crown should be expanded. Control the large number of summer and autumn shoots to restore the tree, and the autumn shoots are decided to stay according to the growth and growth part. Bagging after fruit thinning can avoid the harm of rain, strong sunlight and diseases and insects to citrus fruits, and effectively reduce fruit cracking. In addition, exogenous hormones can alleviate citrus fruit cracking and increase peel crack resistance. One of the reasons why "Ganping" became a noble fruit was the thin skin. Foliar fertilization with triasanol 1mg/L + 0.3% ~ 0. 5% potassium dihydrogen phosphate at the end of June to early July, or foliar fertilization with gibberellin 30mL/L + triacosanol 1mg/L at the end of June and early July, 2 consecutive times at 7d intervals.
4 Discussion and conclusions
Citrus fruit splitting is related to variety hereditary, rootstock, orchard soil moisture content, mineral nutrition, and fruiting amount. Hong Dandan believes that the "Ganping" orchard can be covered with a top film to alleviate the occurrence of fruit cracking. Lai Chengchun reported that the rapid growth of the longitudinal and horizontal diameter of mandarin orange was closely related to the occurrence of fruit cracking, and the lack and irregular change of soil moisture in orchards were the key external factors leading to fruit cracking. Wang Junxiu The results showed that the potassium content of citrus vegetative branches was significantly negatively correlated with the fruit cracking rate, and the occurrence of fruit cracking could be avoided or reduced by appropriate application of potassium and calcium fertilizer. The results of this trial are basically consistent with previous reports.
In summary, water is an important influencing factor of "Ganping" fruit splitting. Supplementation of mineral elements such as potassium and calcium can significantly reduce fruit cracking. In the Leshan area, it is recommended to strengthen the field management of citrus orchards, especially in August ~ September, and pay attention to the occurrence of fruit cracking. When conditions permit, try to use rain-sheltered cultivation, which is an effective measure to prevent citrus fruit cracking.
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