17 - Physiological disorders and their management

Abstract

Physiological disorders are a result of dysfunction or malfunction of the physiological processes of the fruit tissues due to abiotic stresses (temperature, RH, moisture/water stress, chemicals, and nutrient excesses and deficiencies). These disorders reduce the market value of citrus fruits. Most physiological disorders are incurable once they develop—prevention is the best solution. Sunburn, granulation, and fruit cracking are preharvest disorders related to climate and management practices during fruit growth in orchards. If fruits with sunburn injuries or granulation are stored, they deteriorate rapidly. Granulation and regreening generally take place because of a delay in harvesting. Other physiological disorders caused by preharvest factors include boron and copper deficiency, zebra skin, and water spotting. The postharvest development of disorders depends on management of temperature, humidity, and handling practices. Injuries and disorders on the surface and inside the fruit are manifested slowly, as in the case of chilling injury, oleocellosis, and rind breakdown. Most disorders appearing on the surface of various citrus fruits are related to the rupture of oil glands, phytotoxic injury to tissues, and subsequent water loss. The symptoms and control measures of some important disorders such as chilling injury, rind staining, granulation, puffiness, fruit cracking, kohansho, peteca, stem-end rind breakdown, stylar-end breakdown, and creasing are discussed.