Post harvest physiology Majid Javanmard
Apple
Bitter pit is a disorder in apple fruits, now believed to be induced by calcium deficiency. It occurs less commonly in pears. The disease was probably first reported in Germany where it was known as Stippen. It was also known as "Baldwin spot" and "blotchy cork" in North America. The name "bitter pit" was first used by Cobb in Australia in 1895.The disease has been shown as non-pathological and is now known as a disorder. When it occurs on the tree, it is known as "tree pit"; it may also occur in storage, when it is known as "storage pit".
Symptoms The affected fruit have dark spots, about ½ cm diameter, which occur on the skin and/or in the flesh The cells in the spots are dead (necrotic), and turn brown-black.
Causes Early reports indicated that the disorder was affected by climate and growing conditions. Dry weather before harvest seemed to increase the condition. Light crops, heavy use of fertilizers, large fruit and early harvesting increased the condition. Fruit that were free of bitter pit at harvest were often severely affected after a short period of storage. Bitter pit has been widely reviewed over many decades. [4][5][6][7][8] The disorder became a major problem for exports from the Southern Hemisphere to Europe. The breakthrough in control came with the discovery in North America that the mineral calcium was low in affected fruit. This was confirmed elsewhere. [9][10][11]
Control This involved dipping the fruit in the calcium solution and rinsing in water after about 36 hours Several decades of research in several countries with many cultivars showed that moderate levels of bitter pit could be controlled with the spraying of the trees with calcium chloride or calcium nitrate during the growing season It appears that bitter pit can generally be reduced by using good horticultural practices. Usually spraying though out the growing season with a calcium salt is also necessary for moderately susceptible cultivars.
Physiological Disorders Bitter pit Bitter Pit
Watercore All apple growing regions but especially arid or semi-arid climates. Susceptible varieties include Jonathan, Delicious, Stayman, Winesap, Granny Smith and Fuji. Water core is associated with high maturity fruit. Low night temperatures in fall hasten maturity and promote watercore development. Watercore is promoted by large fruit, high leaf to fruit ratio, high fruit nitrogen and boron, low fruit calcium, excessive thinning, high light exposure, Ethrel sprays, and girdling of trunks and limbs. Another type of watercore which is unrelated to maturity may occur during unusually hot weather. This watercore is found more on the exposed side of the apple and may be associated with sunscald.
Symptoms A preharvest disorder resulting in water soaked regions in the flesh, hard and glassy in appearance, only visible externally when very severe. Water soaked areas are found near the core and around the primary vascular bundles but may occur in any part of the apple or involve the entire apple. Symptoms often increase rapidly as fruit become overmature but does not increase postharvest. If symptoms are mild to moderate, they may disappear completely in storage. However, when watercore is severe, internal breakdown can develop.
Control The most effective way to reduce the incidence of water core is to avoid delayed harvests. As fruit approach harvest maturity, samples of fruit from the southwest quadrant of the tree should be cut to look for water core. Fruit should be harvested before water core develops extensively. A subsample of fruit at harvest should be cut prior to storage. Lots with moderate to severe water core should not be placed in CA storage but should be marketed quickly
Causal factors Internal breakdown occurs most often on large, overmature apples. It is also favored by delays in harvest and in cooling and by storage at temperatures above those recommended for the variety. Internal breakdown indicates the approaching end of the storage life of apples when they are not affected by fungus rots. It may, however, occur earlier than normal as a result of unfavorable growing conditions or certain handling or storage practices and may follow water core (second photo), freezing, or bad bruising.
Control measures The little that can be done to control internal breakdown after picking is best done by placing fruits promptly in cold storage at 31 to 32 F. Fruits with a decided tendency toward breakdown cannot be relied on for late keeping even in cold storage. Seriously watercored fruits should be marketed as soon as possible.
Russeting
Russeting is a brown, corky netlike condition on the skin of apples. It may appear on only a small portion of each fruit, or may cover its surface. Severe russeting may be accompanied by fruit cracking which usually renders the fruit useless. Russeting has been associated with specific environmental conditions, damage from harsh chemicals, excess nitrogen, or infection by certain fungi, bacteria and viral organisms. The fruit of younger or vigorously growing trees seem more prone to russeting than older and slower-growing trees. A little russeting is normal on certain varieties of apples, crabapples, and pears, and is not considered a defect in these varieties. 'Chestnut' crab is a good example.
Here are suggestions for reducing it, however. Plant varieties such as Sweet Sixteen, Fireside, or Honeycrisp, that are known not to be prone to russeting. Avoid spraying emulsifiable concentrates (ECs). Do not apply chemicals during slow drying conditions, high humidity, or temperatures above 90 F. Prune properly to encourage good air circulation and speed fast drying after rains. Thin fruits to only 1 or 2 per cluster within 3-4 weeks of peak bloom. Fertilize a bearing tree only if the main shoots grow less than 8" a year. Have the soil analyzed at the University Soil Testing Laboratory to determine its fertilizer needs.
Citrus fruit
Creasing or Albedo breakdown
The albedo or mesocarp is the white spongy material located between the fruit segments and the outer leathery peel or flavedo. Albedo breakdown is the loss of cohesion in the cells if this white layer under the skin and any stress imposed on this as a result of expansion of the pulp can lead to rotting of this layer. It is also associated with creasing in the fruit. Good nutrition - particularly with calcium - helps to minimize breakdown of albedo tissue.
Dry fruit or granulation
Frost injury
Frost damage on citrus fruits appears as dehydrated, dry pulp that occurs following exposure to cold temperatures. Within a few hours of a frost, the fruit's juice vesicles begin to rupture because ice crystals are forming inside them. Fruits are still usable for a short period after the frost but will begin to deteriorate within a few days. Frost damage to citrus trees also appears as water-soaked areas on leaves and twigs followed by withering and browning or blackening of tissue. Frostdamaged citrus trees are not pruned to remove injured portions of wood until early spring when the total extent of dieback becomes clear.
Fruit splitting
One of the most commonly grown citrus is the orange. Orange rinds split open, as well as mandarins and tangelos, but never grapefruit. Navel oranges are the most prone to the problem. So what causes oranges to split? The rind splits because water and plant sugars travel to the fruit too quickly for it to produce enough rind to hold the substances. The excess fluids cause the skin to burst. Young trees have the highest incidence of oranges splitting. Most cases of splitting citrus fruit occur in July to November. Over fertilizing will also cause the problem. The nutrient needs of oranges should be 1 to 2 lbs. of nitrogen annually. You should break up the application into three or four periods. This will prevent too much food, which will make orange rinds split open and possibly crack.
Oleocellosis
Potato
Black Spot
Black heart
Greening
Skinning
Hallow heart
Tomato
Blossom end rot
Blossom-end rot is a disorder of tomato, squash, pepper, and all other fruiting vegetables. You notice that a dry sunken decay has developed on the blossom end (opposite the stem) of many fruit, especially the first fruit of the season. This is not a pest, parasite or disease process but is a physiological problem caused by a low level of calcium in the fruit itself.
BER, or blossom-end rot usually begins as a small "water-soaked looking" area at the blossom end of the fruit while still green. As the lesion develops, it enlarges, becomes sunken and turns tan to dark brown to black and leathery. In severe cases, it may completely cover the lower half of the fruit, becoming flat or concave, often resulting in complete destruction of the infected fruit.
Calcium is required in relatively large concentrations for normal cell growth. When a rapidly growing fruit is deprived of calcium, the tissues break down, leaving the characteristic lesion at the blossom end. Blossom-end rot develops when the fruit's demand for calcium exceeds the supply in the soil. This may result from low calcium levels in the soil, drought stress, excessive soil moisture, and/or fluctuations due to rain or overwatering. These conditions reduce the uptake and movement of calcium into the plant, or rapid, vegetative growth due to excessive nitrogen
Adequate preparation of the garden bed prior to planting is the key to preventing BER. Insure adequately draining soil in the bed by adding needed ammendments, maintain the soil ph around 6.5 - a ph out of this range limits the uptake of calcium. Lime (unless the soil is already alkaline), composted manures or bone meal will supply calcium but take time to work so must be applied prior to planting. Excess ammonial types of nitrogen in the soil can reduce calcium uptake as can a depleted level of phosphorus. After planting, avoid deep cultivation that can damage the plant roots, use mulch to help stabilize soil moisture levels and help avoid drought stress, avoid overwatering as plants generally need about one inch of moisture per week from rain or irrigation for proper growth and development.
Fruit cracking
Fruit cracking in tomatoes can be a serious market problem, reducing profits. The causes of fruit cracking are varied and are subject to debate by researchers. Several factors have an effect on fruit cracking. This can range from splitting to skin russeting. Water uptake, humidity, temperature and soluble solids (sugars) as well as calcium nutrition and standing water on the fruit are thought to have roles in fruit cracking, along with genetics. Cultural practices can have an effect on fruit cracking. Water management, light levels and rate of fruit development can be affected by management practices. Greenhouse growers should be aware of potential problems with increased fruit cracking in tomatoes with some cultural practices. Increased light and fruit growth can occur when new plastic is put on or with topping to increase fruit size. Watering schedules may need to be modified to reduce cracking under those conditions.
Catfaced fruit
Cat-facing is a physiological disorder of tomatoes. Cat-face originates in the early stages of flower bud development and is the result of abnormal development of plant tissue between the style and ovary which results in misshapen fruit. Other impediments to flower bud development can also result in catfacing. The syndrome is related to unfavorable growing conditions, in particular several days below 60 F when the plants are young. High levels of soil nitrogen and excessive pruning aggravate the problem. Accidental exposure to phenoxy herbicides can also lead to malformed fruit. Cat face is more prevalent on large-fruited, fresh market tomato varieties. Good growing practices, especially temperature control, should be followed in greenhouse production of field transplants. Excess nitrogen, aggressive pruning, and accidental exposure to hormonal herbicides should be avoided.
Blotchy ripening
Tomato Blotchy Ripening
Blotchy ripening is most often found in greenhouses and damage to fruit may be significant. It can also be encountered in the field in fresh-market and processing tomato crops. The cause of this physiological disorder and its relationship to "gray wall" is not well understood. Blotchy ripening has been linked to potassium and/boron deficiency and to high nitrogen levels, which promote excessive growth. This syndrome has sometimes been attributed to infection by Tomato Mosaic Virus, but this does not seem to be the definitive cause. Weather plays a role in the development of blotchy ripening; the disorder is more prevalent when temperatures are very high. Affected fruit ripen unevenly, with hard, gray to yellow patches. The patches do not turn red, but remain gray or turn yellow. When fruit are cut, the vascular tissues may appear brown and rotted. Growers should provide balanced fertilization and, in greenhouses, avoid excessively high temperatures, if possible. Cultivars vary in susceptibility to this disorder.
Cork Spot
Cork spot, bitter pit and Jonathan spot are similar in that damage to tissue occurs mostly on the surface and in cell tissue just below the surface. Although apples affected with these disorders are edible, the unattractive external appearance often arouses consumer concern and reduces salability of fruit.
Occurrence of cork spot and bitter pit appears to be related to reduced calcium availability in the developing fruit. Cork spot commonly occurs on York Imperial and occasionally on Delicious and Golden Delicious. Bitter pit can occur on many cultivars, but is most common on Granny Smith, Delicious, Grimes Golden and Northern Spy in Ohio. Low soil ph, light crops and excessively vigorous shoot growth are associated with increased incidence of these disorders. Jonathan spot, however, appears to result from toxins accumulating in the lenticels of the fruit skin. Although Jonathan is the most susceptible cultivar, Wealthy and Rome Beauty are also moderately susceptible to this disorder. Symptoms, time of occurrence and control measures available at this time are described below for each specific disorder.