Dear Dr.Taain
Cork spot occurs during the growing season, and is characterized by localized green to brown sunken spots on the fruit or in the flesh. The spots in the flesh, which may or may not develop just under the skin, are brown, corky, dead tissue, and are more prominent toward the calyx half of the apple. The spots in the flesh have a bitter taste. Under severe conditions, fruit cracking can occure.
In a research, biochemical changes occurring during the development of cork spot of ‘York Imperial’ were investigated. At the first visible sign of the disorder, the rate of ethylene production increases in the affected tissue. Respiration also increases, acetate being the major respiratory substrate rather than glucose. Protein synthesis, pectin synthesis, and the movement of inorganic ions into the tissue follow. During the time the chemical changes are taking place in the tissue, abnormal cell division is initiated, packing the newly-formed cells into the intercellular spaces. At the final stage of development, the tissue becomes brown and appears as a firm brown spot in the flesh of the apple (Faust, M. & Shear, C.B. Plant Food Hum Nutr (1969) 19: 255-265).
The best long-term control for cork spot is the addition of agricultural ground limestone to the soil at planting, according to soil test recommendations. Limestone should be added at three to five year intervals after planting, based on soil tests. In addition to soil liming, calcium sprays may help to reduce the incidence of cork spot in established apple planting. Calcium chloride at 2 pounds per 100 gallons water applied in four sprays beginning two weeks after full bloom and continuing at 10 to 14 day intervals thereafter may help to reduce cork spot. Calcium chloride at this rate may be added to pesticide sprays normally used in controlling post-bloom diseases and insects affecting fruit. Do not apply calcium chloride sprays when temperature is above 85 F. Rinse sprayer thoroughly after use because calcium chloride is highly corrosive. Reduce excessive shoot growth by reducing or not applying nitrogen to the soil of apple trees for one to two years. Remove excessive growth and water sprouts with summer pruning in late July or early August.
I also suggest adding the words of cork spot, physiological abnormality and post-harvest to the keywords of your question to further contribute to other researchers.
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