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Physiological abnormalities in citrus

Tissue damage or disturbance of fruit metabolism due to factors other than diseases and mechanical injuries is called physiological abnormality. Abnormal factors can be divided into two categories: internal factors such as aging and environmental factors such as frostbite. External disorders are easier to control than internal ones. By paying attention to the temperature, relative humidity and the composition of the atmosphere inside the warehouse, especially the amount of ethylene, the quality of the fruit can be maintained.

Tissue damage or disturbance of fruit metabolism due to factors other than diseases and mechanical injuries is called physiological abnormality. Abnormal factors can be divided into two categories: internal factors such as aging and environmental factors such as frostbite. External disorders are easier to control than internal ones. By paying attention to the temperature, relative humidity and the composition of the atmosphere inside the warehouse, especially the amount of ethylene, the quality of the fruit can be maintained.

Fruit granulation
Valencia oranges are one of the citrus fruits that are most exposed to a phenomenon called granulation. This physiological phenomenon occurs when the fruit remains on the tree after ripening until late summer or autumn. Anatomical studies have shown that in this case, the sacs containing the juice or vesicle become large and hard, and their color turns white. In case of severity of this complication, the internal quality of the fruit changes completely and it becomes dry and fibrous inside the fruit. Granulated bodies have been reported to have higher respiration rates and lower acidity and sugar levels because some of the material is used to build and harden the cell wall. In trees with few fruits, the phenomenon of granulation is severe, while in high-yielding trees, this complication is less reported. Factors such as base type, tree age, rainfall and tree growth area affect this phenomenon.

 

Fruit burst

Fruit bursting is observed in citrus fruits, especially in some cultivars such as pomegranate oranges and page tangerines during the fruit development period. This sensitivity is higher in some cultivars than in others. The main cause of this phenomenon is not known for sure, but there are factors involved in causing this problem. Environmental factors that affect temperature and humidity or cause sharp fluctuations in soil moisture have a serious impact on fruit bursting. Severe copper deficiency is another factor that causes hardening of the skin of the fruit and in parallel with the development of the fruit, the skin of the fruit does not develop and causes the skin to rupture. On the other hand, diseases such as black rot and alternaria often play a role in causing this complication.

Shortcut cracking
Shortcut cracking is a physiological complication with unknown factors that is observed in all citrus fruits, especially Hamlin oranges and tangerines. Symptoms include the appearance of regular and sometimes irregular bumps on the skin of the fruit without cracking the skin. In severe cases, these roughnesses develop longitudinally and transversely on the skin and cover the entire skin. Examination of cellular tissue changes in the developing skin of the orange fruit revealed that the complication of short-term cracking is due to cell separation and changes in their chemical composition and wall structure, and cell disintegration can not be the cause of this complication. This complication seems to be related to the nutritional status of the tree and feeding with potassium and nitrogen reduced the rate of this complication.

 

Frostbite

Temperature is one of the most important factors in maintaining fruit quality after harvest. Stimulation of processes associated with fruit decay, respiration, tissue changes, vitamin C depletion, and ultimately high quality is achieved at temperatures above the cold damage limit. In citrus, cold occurs at low temperatures and close to the freezing point. Storing fruits at 12 degrees for 2-3 weeks develops this complication. Factors such as too early or too late harvest, low relative humidity increase the superficial spot insufficiency on the fruit. Step-by-step maintenance for 2-3 weeks at 10 ° C, then 3 weeks at 5 ° C is effective in controlling cold damage. Waxing reduces and does not eliminate this phenomenon.

Sun burn

Sunburn damages leaves, stems and fruits. It creates gum spots on the leaves that sometimes look black and greasy. It is more likely to occur in fruits located in the southwest direction.

Disintegration of the skin where the fruit connects to the stem
One of the most common skin damage in citrus is caused by dehydration. Damaged fruits are prone to rot. Which is often common in oranges. Thick-skinned fruits are more sensitive than thin-skinned ones. By destroying the skin tissue in the area where the fruit connects to the stem, it creates sunken brown areas with irregular shapes. The most important causes of this complication are imbalance in the amount of nitrogen and potash, decrease in fruit moisture after harvest and before waxing. Damages can be reduced by observing issues such as reducing the distance between harvest time and waxing, keeping fruits in high relative humidity and preventing severe brushing during packaging.

Oil stain

Due to the destruction of oily cells located in the tissue of the flado and the oil inside them is removed. This oil is toxic and destructive to skin surface cells and causes necrotic phenomena in surface cells. This phenomenon occurs mostly after a night when the pores of leaves and fruits are closed and the cells are at maximum inflammation. In order to reduce this complication, the fruit should not be harvested until its inflammation has decreased.

piting

This complication is characterized by the appearance of a series of sebaceous glands that are destroyed and spread on the surface of the skin. The destroyed areas are gradually tanned and extend to near the Golgah area. The likelihood of developing this complication is directly related to fruit size and low oxygen content in the fruit tissue. Increased respiration due to high storage temperature and reduced gas exchange in the presence of high-gloss waxes can be the reasons for the prevalence of pitting. To control the pitting, the temperature of the fruit flesh should be around 10 degrees Celsius or less. Cold damage may increase at temperatures below 9.5. The use of wax coatings with relatively low luminosity reduces the amount of pitting due to the increase in gas permeability.

پفکی کردن

The peeling of the fruit from the flesh during storage of the fruit in storage is called puffing. According to the evidence, strong trees and high-moisture stores cause the skin to thicken and separate from the flesh. This phenomenon is less common in oranges and lemons but is more common in tangerines. Pre-storage curing and proper ventilation reduce puffiness.

Source:

Citrus cultivation in Iran
Author: Dr. Reza Fotouhi Qazvini, Dr. Javad Fattahi Moghaddam