Physiological Disorders in Tomato Fruit Development

Physiological disorders are abnormalities in fruit color or appearance that are abiotic in origin. These abnormalities are often confused with damage from pathogens or insects (biotic damage). Physiological disorders are distinguished from deficiencies of a single nutrient, and physical, chemical or herbicide injury. Causes of physiological disorders include genetic susceptibility, environmental factors, watering practices, nutrition, and cultural practices such as pruning and training. For most physiological disorders, a number of factors are involved, and there is almost always a genetic component. This complex interplay of factors is poorly understood for most disorders, and in some cases contradictory results have been reported. There are also a number of different names for many disorders. Although there are many interactions, for the purposes of this discussion, physiological disorders are divided into groups: nutrient imbalances, especially between potassium and nitrogen or magnesium (blotchy ripening, greywall); calcium amount or movement into the fruit (gold fleck or speck, blossom-end rot); temperature extremes (catfacing, boat fruit, rough fruit, puffiness, sunscald); genetic predisposition (green or yellow shoulder) and watering (cracking, russeting, rain check, shoulder check). Secondary effect of pathogens or insects (ghost spot from Botrytis, dimpling from thrips, uneven ripening from silverleaf whiteflies, patterning as a result of tomato spotted wilt or pepino mosaic virus) can also be considered physiological disorders, but are not reviewed here since the cause is biotic.