Fruit cracking affects numerous meaty fruits, such as sweet cherry, plum, apricot, apple, litchi, pomegranate, citrus, banana, avocado, grape, persimmon, peach, tomato, and pistachio. Besides affecting different fruit species, this peel disorder presents its variability within the fruit species and within different climates as well. While various factors contribute to fruit cracking, climatic conditions play a crucial role in its occurrence.
Fruit cracking, in most instances, takes place when plenty of water is made available to the plants, succeeding a prolonged drought. It is considered that during arid periods, both xylem and phloem get further strengthened, resulting in lost ability of dividing and enlarging. In cases where after a dry spell water supply is swiftly increased, the meristematic tissues resume growth, but not the xylem and phloem. This causes the harder tissues to get ruptured. Furthermore, due to high temperature and low humidity in summer, the peel of fruits become hard and inelastic. The pressure of the internal tissues towards the skin peel increases, resulting in the cracking of the fruit.
Environmental factors, such as temperature and its fluctuations, such as sudden temperature drops between day and night, and humidity, have been demonstrated to have an influence on fruit cracking. Other weather conditions, for example, wind velocity, air relative humidity, canopy temperature, and fruit surface temperature, have also been considered as potential causes of cracking. It has been indicated that water stress, indicated by relative water content and water potential of leaves, directly affects the severity of fruit cracking and its incidence.
These physiological parameters are affected by high temperature stress, as measured by canopy air temperature difference and fruit air temperature difference, which are significantly correlated with leaf water potential and relative water content. Temperature-mediated leaf water potential seems to have a direct impact on the occurrence of fruit cracking.
In addition to excessive water absorption by the roots, the osmotic absorption of water through the fruit’s skin also plays a role in fruit cracking in various fruits such as apples, peaches, and cherries. When there is an abundance of water and low evaporative demand, unseasonal rainfall can lead to the cracking or splitting of fruits due to the development of high hydrostatic pressure (turgor pressure) within the fruit, exceeding the tensile strength of the cell walls.
Excessive cell enlargement in fruits resulting from a significant increase in soil moisture is also a cause of fruit cracking in apples and sweet cherries. Excessive water absorption by the fruit through the fruit skin has been also reported as a factor in the cracking of cherries. Irregular and/or excessive irrigation during the ripening period, as well as rainfall during the harvest period, have been identified as causes of cracking in pomegranates. Furthermore, in prune, tomato, and nectarine crops, high-volume irrigation after a period of water stress has been found to result in crack development.
Mineral nutrient deficiency has been also attributed to instances of fruit cracking. For example, cracks in apricots are attributed to a boron deficiency, while cherry and tomato cracking is associated with calcium deficiency. Adequate macro and micronutrients are necessary for the proper growth, development, and productivity, with zinc, iron, boron, potassium and manganese being particularly limiting micronutrients in pomegranates cultivated for commercial use.
Potassium, calcium, zinc, copper, molybdenum, and manganese are involved in physiological processes during the fruit growth period, and their deficiencies can significantly affect the fruit quality, including the skin peel integrity. Boron is believed to be essential for meristem growth and normal tissue development by influencing enzyme activity.
Calcium is essential for proper plant growth and development as it plays metabolic roles in nutrient uptake and contributes to abiotic and biotic stress resistance. Calcium likely contributes to the elasticity, strength, and thickness of epidermal cell walls, aiding in resistance against cracking under high turgor pressure during water stress. Zinc foliar spray has been found to reduce cracking and improve fruit yield, most likely due to its impact on water uptake, transport, and enzyme activities involved in protein, carbohydrate, and nucleic acid metabolism.
Zinc also regulates the absorption of water by plant roots. Antitranspirants have been observed to reduce fruit cracking by reducing stomatal opening, increasing leaf resistance to water vapor diffusion without affecting carbon dioxide uptake, regulating fruit skin elasticity, and reducing transpiration rates.
