Physiological disorders
Physiological disorders are caused by non-pathogenic agents that affect fruit quality. Usually, aesthetic quality is degraded. The cause can be either one or a combination of environmental, genetic, or nutritional factors. Fruit Disorders Misshapen melons (gourd-necked or bottle necked) are frequently produced by varieties with long fruit. Moisture stress is a cause. Occasionally melons of any variety may be misshapen because they lie on uneven ground or were damaged while small in size. Misshapen or pear-shaped fruit can also be caused by poor pollination that leads to restricted growth at the stem end because of the absence of developing seeds. Poor pollination can be minimized by increasing the number of beehives in the field. Low temperatures can also cause misshapen fruit. Blossom-end rot is a deterioration of the blossom end of the fruit. The usual order of development is softening, slight shriveling, browning, blackening with extensive shriveling, and sometimes secondary decay. Poor calcium nutrition and moisture stress cause blossom-end rot. Hot, dry winds, nematode damage, excessive fertilizer, low levels of calcium in the soil, pruned roots from late cultivation and other conditions are contributing factors. Bursting may result from an uneven growth rate, which is particularly associated with heavy rainfall or irrigation when the fruit is maturing. The percentage of bursted fruit is usually low, and types with round fruit are more susceptible. White heart is white streaks or bands of undesirable flesh in the heart (center) of the fruit. This is caused by excessive moisture (and probably too much nitrogen) during fruit maturation. Hollow heart is a disorder that varies among varieties. Hollow heart is marked by cracks in the heart of the watermelon fruit owing to accelerated growth in response to ideal growth conditions facilitated by ample water and warm temperatures. Sun scald (burn) results from exposure to intense solar radiation that leads to dehydration and overheating damage of the rind tissue. Sun scald can be alleviated by covering the fruit with vines or straw material. Sunburn occurs most frequently in varieties that have dark-green rinds. Charleston Gray types and other melons with grey-green rinds rarely suffer from sunburn. Good, healthy foliage will minimize sunburn damage as well as favour good yields and quality. Strong winds can blow unprotected vines away from the developing fruit along the edges of the rows and cause full exposure of the fruit to the sun. Rind necrosis is an internal disorder of the watermelon rind. Symptoms are brown, corky, or mealy textured spots on the rind which may enlarge to form large bands of discoloration that rarely extend into the flesh. Experienced pickers often can detect affected melons by the subtle knob- biness that is visible on the surface of affected melons. The cause of rind necrosis is unknown. Bacterial infection has been reported to be a cause, although similar bacteria are found in healthy melons. Drought stress also is reported to predispose melons to rind necrosis. Cross stitches are elongated necrotic wounds (2 cm long) that are perpen- dicular to fruit length. The cause of cross stitches is unknown. |
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