Symptoms

The characteristic symptom of tiger skin disease is that the fruit skin turns brown if it is scalded by water. It mostly occurs on fruits that are under-ripened and poorly colored, or on the shady side of the fruit that is not colored. It develops first, and in severe cases spreads to the sunny side of the coloration. In the early stage of the disease, the fruit surface turns light yellowish brown and forms unshaped patches, but they are not very obvious. Later, the diseased area will become darker in color and slightly sunken; in severe cases, dozens of layers of cells under the skin will turn brown, and the peel can be torn off. The pulp becomes soft, loses its normal flavor, and smells of alcohol. In the later stages of the disease, the diseased fruits are susceptible to damage by Penicillium and other pathogens and become rotten.

Causes and occurrence patterns

Long-term research has been conducted abroad on the causes of apple skin disease. Studies by Hugh Lin and others have shown that apple fruit wax produces a volatile terpene-rich hydrocarbon α-farnesene, which can auto-oxidize to produce unconjugated trienes that damage peel cells and cause tiger skin disease. In fruits that are sensitive to tiger skin disease and fruits that are harvested too early and with insufficient maturity, the content of α-farnesene is relatively high and is most active 6-8 weeks after harvest. However, due to the presence of fruit wax during the harvest period, The content of natural antioxidants is also high, and the accumulation of harmful substances does not reach the level of poisoning, so no symptoms appear. As the storage period prolongs, the natural antioxidants gradually decrease, harmful oxides gradually accumulate, and diseases appear under suitable external conditions.

Fruit maturity is closely related to the occurrence of tiger skin disease. Most varieties stored in autumn in my country suffer from tiger skin disease to varying degrees. The Guoguang variety is the most sensitive, followed by Japanese Jin, Hongguan, Hongxing, Marshal, Bailong, Jiguan, India and other varieties. Golden Delicious and Carnelian are less sensitive. Apples harvested too early are prone to disease due to insufficient maturity. As the harvest period is postponed, the incidence decreases significantly. Tiger skin disease mostly occurs on green fruits with poor coloring. On the same fruit, the disease occurs earlier and more severely on the shady side than on the sunny side. The occurrence of tiger skin disease is related to the degree of fruit senescence. Taking red star variety apples as an example, if the hardness of apples is stored until mid-March and drops to 3.1-3.6kg/cm2, the incidence rate is more than 40%, while if the hardness is above 4kg/cm2, the incidence rate is less than 8%. The more senescent the fruit is in the later stages of storage, the more susceptible it is to the disease.

Storage temperature has a great influence on the occurrence of tiger skin disease. The higher the storage temperature, the more frequent and severe the disease will be. Ventilation conditions also have an impact. Apples that are loosely packed or well ventilated during storage are less likely to be infected than apples that are tightly packed and poorly ventilated. During the growth period, any cultivation and climatic conditions that may cause delayed fruit maturity, such as heavy application of nitrogen fertilizer during the autumn shoot growth period, excessive pruning to stimulate branch growth, heavy rain or irrigation in autumn, and low temperature and high humidity during the growth period, etc., can all promote The disease worsens.

Prevention and control methods

1. Harvest at the right time according to the variety and avoid premature picking.

2. Avoid taking measures to delay fruit ripening

When fertilizing, avoid applying nitrogen fertilizer alone and apply phosphorus and potassium fertilizer together.

3. Promote cold storage and controlled atmosphere storage.

4. Storage ventilation

Exhaust ethylene from the storage.

5. Fruits wrapped in medicinal paper or fruits soaked in pharmaceuticals

Use products containing diphenylamine (each paper contains 1.5-2.0mg) or ethoxyquin (each paper contains 2mg) Use fruit wrapping paper to wrap the fruits, or soak the fruits with 0.1% diphenylamine solution and 0.25-0.35% ethoxyquin solution.