Physiological disorders of mango

S. Parthasarathy, Ph.D Scholar, Dept. of Plant Pathology, TNAU, Coimbatore-3

        Exposure of mango fruit to various environmental, cultural and post-harvest handling treatments often leads to tissue abnormalities which are quite distinct from those induced by pathological and entomological agents. These types of abnormalities are generally termed as physiological disorders. The complexity of events leading to their occurrence often makes it more difficult to define the causal factors than is the case for post-harvest diseases or pests.

        Physiological disorders are usually the result of imbalances in metabolism induced by some factor in the pre-harvest or post-harvest environment that leads to cell collapse and the appearance of water- soaked brown areas on some part of the fruit. Pre-harvest factors that predispose mango to physiological disorders include growing location, orchard. condition, tree nutrition and conditions at harvest while post- harvest storage conditions such as temperature, oxygen and carbon- dioxide levels, packaging and surface coating treatments are contributing factors to the occurrence of the disorders.

Conditions such as soft-nose, tip-pulp, internal breakdown or soft-centre or spongy-tissue have been described in literature. Some of the physiological disorders are described below.

Chilling injury is manifested initially as a brown discoloration of the skin often accompanied by pitting but in more severe cases the skin colour becomes more pronounced and the flesh is affected. There is also uneven ripening with poor colour and flavour development and the fruit is prone to develop rots. It is generally accepted that storage of all cultivars of mango below 10°C renders the fruit susceptible to develop chilling injury although the time required to show visible symptoms varies between cultivars. It has been found that most cultivars can be safely stored for two to four weeks near 10°C and then ripened normally when subsequently returned to ambient temperature.

Internal breakdown has been observed in some varieties of mango subsequent to storage in polythene bags or polyvinyl chloride wraps. Waxing also invariably causes this disorder. Apart from failure of the peel colour to advance to a full yellow stage, affected fruit do not exhibit external symptoms. Symptoms in the mesocarp range from pale flesh colour to the development of delineated starchy areas with airpockets, a condition termed spongy tissue. Severely affected fruits are characterized by a considerably reduced flesh firmness, uneven peel and pulp ripening, reduced total soluble solids and elevated titrable.

Lumpy tissue (called heb in Thailand) is prevalent in several Southeast Asian varieties. This disorder is characterized by the development of indentations in the peel, which become wider and deeper as the fruit approaches senescence. The mesocarp of affected fruits contains white lumps. The necrotic areas have been found to consist of ruptured cells surrounded by intact cells loaded with starch. Here are no reports of the etiology of this disorder.

Ricey disorder, also of unknown etiology, is commonly observed in ripened mango. Affected fruit show no external symptoms, but small lesions about the size of rice grains, delineated by tissue with cotton- like appearance, can be observed in the mesocarp. The sensory attributes are generally unaffected.