Here is a list of fruit disorders with their control:- 1. Mangoes 2. Banana 3. Grapes 4. Lemon 5. Guava 6. Apples 7. Litchi 8. Papaya 9. Fig 10. Pear 11. Plum 12. Peach.
Contents:
- Disorders of Mangoes and Its Control
- Disorders of Banana and Its Control
- Disorders of Grapes and Its Control
- Disorders of Lemon and Its Control
- Disorders of Guava and Its Control
- Disorders of Apples and Its Control
- Disorders of Litchi and Its Control
- Disorders of Papaya and Its Control
- Disorders of Fig and Its Control
- Disorders of Pear and Its Control
- Disorders of Plum and Its Control
- Disorders of Peach and Its Control
1. Disorders of Mangoes and Its Control:
Physiological and Physical Disorders:
Some disorders, such as chilling injury and high CO2 injury, are induced after harvest, while others are inherent. Inherent disorders occur intermittently, and are unpredictable, such as jelly seed, which results in watery, translucent tissue around the seed giving an over-ripe appearance. It does not develop after harvest unless it was present at harvest.
Some cultivars are very susceptible. Soft nose and internal breakdown (or spongy tissue) are other disorders, though it is possible these are one in the same. Sap burn is a major problem with some cultivars such as Kensington, while Irvin is less susceptible, water/detergent washing helps to avoid damage.
The important physiological disorders are:
1. Alternate Bearing:
The south Indian varieties are regular-bearer, whereas north Indian ones alternate-bearer. Paclobutrazol helps in flower induction in mango. It is used @5 g and 10 g/tree as soil drenching with results in minimum outbreak of September to October vegetative flushes, giving an early and profuse flowering and more annual yield without affecting fruit size and quality.
2. Mango Malformation:
Mango malformation causes huge losses in Punjab, Delhi and Uttar Pradesh and to some extant in Gujarat, Maharashtra, Bihar, West Bengal and Orissa.
i. Vegetative Malformation (Bunchy Top):
It is common in nursery seedlings and young plants while floral malformation affects trees at the bearing stage. In this disorder the leaves become compact and a bunch is formed at the apex of shoot or in the leaf axil hence growth of shoot-let is arrested.
ii. Floral Malformation:
The incidence of disorder varies from variety to variety. It affects the productivity. Deblossoming alone or coupled with a spray of 200 ppm NAA lowers the number of malformed panicles significantly.
3. Black Tip:
Black tip disorder is observed in Punjab, Uttar Pradesh, Bihar and West Bengal. The distal-end of the affected fruits turns black and becomes hard and fruits ripen prematurely. Fruits cannot be sold out in market.
Black tip develops due to smoke of brick-kilns located within a distance of 600 m which release gases like carbon monoxide and carbon dioxide, sulphur dioxide and acetylene. It can be controlled by raising the height of the chimney of the brick-kilns. Spraying borax (0.6%) at 10-14 days intervals (jhumka) starting from fruit set also controls it.
4. Clustering (Jhumka):
This is the clustering (Jhumka) at the tip of the panicle and appears as of bunch tip. These become dark green with a deeper curve in the sinus beak region. These fruit lets grow to marble size and growth ceases. Clustering develops due to adverse climate mainly low temperature in February-March. Most of the fruits ate aborted with shriveled embryos and do not develop further, signifying the role of normal embryo growth in the development of fruits.
5. Spongy Tissue:
Fruits from outside look normal but from inside a patch of flesh becomes spongy, yellowish and sour this disorder. It is specific in Alphonso mango. This disorder reduces export of this variety. The tissue becomes spongy due to inactivation of ripening enzyme induced by high temperature, convective heat and post-harvest exposure to sunlight.
Use of sod culture and mulching can reduce this disorder. Varieties like Ratna and Arka Puneet which are hybrids of Alphonso do not suffer from this malady.
i. Sapburn:
Dark-brown to black discoloration of mango skin due to chemical and Physiological injury from exudate (sap) from cut stem.
ii. Skin Abrasions:
Abrasions due to fruit rubbing against rough surfaces or each other result in skin discoloration and accelerated water loss.
iii. Chilling Injury:
Symptoms include uneven ripening, poor color and flavor, surface pitting, grayish scald-like skin discoloration, increased susceptibility to decay, and, in severe cases, flesh browning. Chilling injury incidence and severity depend on cultivar, ripeness stage (riper mangoes are less susceptible) and temperature and duration of exposure.
iv. Heat Injury:
Exposure to temperatures above 30 °C for longer than 10 days results in uneven ripening, mottled skin and strong flavor. Exceeding the time and/or temperature combinations recommended for decay and/or insect control, such as 46.4°C water dip for 65-90 minutes (depending on fruit size) causes heat injury (skin scald, blotchy coloration, uneven ripening).
v. Internal Flesh Breakdown (Stem-End Cavity):
Flesh breakdown and development of internal cavities between seed and peduncle. This disorder is more prevalent in tree-ripened mangoes.
vi. Jelly-Seed (Premature Ripening):
Disintegration of flesh around seed into a jelly-like mass.
vii. Soft-Nose:
Softening of tissue at apex. Flesh appears over-ripe and may discolor and become spongy. This disorder may be related to calcium deficiency.
Anthracnose (Colletotrichum gloeosporioides), that is due to pre-harvest infection and does not spread postharvest, and the postharvest stem end rots caused by several fungi that infect before and after harvest (often as wound invaders that spread postharvest), are the two most common diseases.
It begins as latent disorders infections in unripe fruit and develops when the mangoes begin to ripen. Lesions may remain limited to the skin or may invade and darken the flesh. It first appears as superficial black spots and streaks that then become sunken.
Alternaria rot (Alternaria alternata), a pre-harvest infection, can sometimes be a problem, while the postharvest wound infections can occasionally be severe such as Black Mold (Aspergillus spp.) and transit rot (Rhizopus spp).
Disease control begins in the field followed by postharvest sanitation, avoidance of latex burn (stain) and mechanical injury. Hot water treatment 46 °C for 60 to 120 min and fungicides can be used, depending on cultivar. Hot water brushing at 55 °C for 20 s shows good control.
Diplodia stem-end rot is caused by Lasiodiplodia theobromae, affects mechanically-injured areas on the stem or skin. The fungus grows from the pedicel into a circular black lesion around the pedicel.
i. Careful handling to minimize mechanical injuries.
ii. Hot water treatment- 5-10 minutes (depending on fruit size) dip in 50°C ± 2 °C water.
Postharvest fungicide (imazalil or thiabendazole) treatment alone or in combination with hot water treatment maintaining optimum temperature and relative humidity during all handling steps.
2. Disorders of Banana and Its Control:
Physiological Disorders:
A condition known as ‘maturity bronzing’ or ‘maturity stain’ has been observed in Australia and Central America at certain times during the year, 20 to 30 days before harvest. The fruit is unacceptable for market although eating quality is unaffected.
This disorder has been associated with water deficits at bunch emergence during rapid fruit growth under very humid and hot conditions. If bananas and plantains are exposed to temperatures above 30 to 35 °C, ripening can be irreversibly inhibited (high temperature injury).
Neer Vazhai (Neer = water and vazhai = banana) is a malady of unknown etiology. The fruits ooze out watery fluid when cut. It affects Nendran banana in Tamil Nadu. Infested plants show poor plant growth, delayed shooting, lanky bunch with few hands and immature unfilled fingers. In infested plants, sever root damage is noted.
Cause of this disorder is not known but is of serious concern causing considerable loss. There are stray reports of this malady affecting ‘Poovan’ around Trichy in Tamil Nadu. Application of growth hormone NAA improves the finger filling. It is transmitted through suckers. Thus it can be suspected to be caused by virus or mycoplasma.
Kotta vazhai (Kottai = seed) is also a malady of unknown etiology affecting Poovan banana. It refers to conspicuously enlarged ovules and immature dark green fruits. Though few studies conducted earlier with sprays of 2, 4-D 120 ppm enabled to obtain normal bunch, the cause of this malady is not known. It is suspected to be associated with incidence of banana streak virus.
Symptoms include surface discoloration, dull or Smokey anal color, sub-epidermal tissues reveal dark-brown streaks, failure to ripen, and, in severe cases, flesh browning. Chilling injury results from exposing bananas to temperatures below 13 °C (56 °F) for a few hours to a few days, depending on cultivar, maturity, and temperature.
For example, moderate chilling injury will result from exposing mature-green bananas to one hour at 10 °C (50 °F), 5 hours at 11.7°C (53°F), 24 hours at 12.2°C (54°F), or 72 hours at 12.8°C (55 °F). Chilled fruits are more sensitive to mechanical injury.
Abrasions result from skin scuffing against other fruits or surfaces of handling equipment or shipping boxes. When exposed to low (<90%) relative humidity conditions, water loss from scuffed areas is accelerated and their color turns brown to black.
Dropping of bananas may induce browning of the flesh without damage to the skin.
The main postharvest pathological diseases of bananas and plantains are crown rot, a disease complex caused by several fungi (Colletotrichum musae, Fusarium semitectum, Fusarium pallidoroseum, Lasiodiplodia theobromae, Botryodiplodia theobromae, Ceratocystis paradoxa, Verticillium sp. Acremonium sp. Curvularia sp.) and anthracnose (Colletotrichum musae).
Anthracnose is a latent infection that occurs in the plantation, although it can appear on green fruit is more apparent in ripening fruit as numerous small dark circular spots. Crown rot organisms normally enter after harvest, usually as a result of mechanical injury to the fruit.
Other diseases that from time to time become important locally include – stem end rot (Lasiodiplodia theobromae / Thielaviopsis paradoxa) where the invaded flesh becomes brown, soft and water- soaked; cigar end rot (Verticillium theobromae / Trachysphaera fructigena) where the rotted tip of the finger is dry and appears similar to the ash of a cigar.
Sigatoka disease of bananas is caused by Mycosphaerella sp. and has been reported in most banana/plantain producing countries. The potential of this fungal disease is such that a flourishing banana industry can be destroyed within a few years. Fruit symptoms include premature ripening, buff-colored pulp, and increased susceptibility to chilling injury.
Preventive and control measures to reduce decay incidence begin with strict sanitation in plantation and packing plant, postharvest treatment with systemic fungicides, minimize mechanical damage during handling, prompt cooling of fruit to lowest safe temperature, and expedite transport to final destination.
This disease is caused by one or more of the following fungi – Thielaviopsis paradoxa, Lasiodiplodia theobromae, Colletotrichum musae, Deightoniella torulosa, and Fusarium roseum which attack the cut surface of the hands. From the rotting hand tissue the fungi grow into the finger neck and with time, down into the fruit.
This is caused by Colletotrichum musae, becomes evident as the bananas ripen, especially in wounds and skin splits.
Caused by Lasiodiplodia theobromae and/or Thielaviopsis paradoxa, which enter through the cut stem or hand. The invaded flesh becomes soft and water- soaked.
It is caused by Verticillium theobromae and/or Trachysphaera fructigena. The rotted portion of the banana finger is dry and tends to adhere to fruits (appears similar to the ash of a cigar).
Minimizing bruising; prompt cooling to 14°C (58°F); proper sanitation of handling facilities; hot water treatments [such as 5 minutes in 50 °C (120°F) water] and/or fungicide (such as Imazalil) treatment to control crown rot.
Suitability as Fresh-Cut Product:
Bananas and plantains are not good candidates for fresh-cut processing because of their very high oxidation and browning potential.
Mechanical damage in bananas and plantains take several forms that vary in importance depending upon the perceptions of consumers. Banana peel is very sensitive to mechanical damage. Export markets for bananas require a blemish- free fruit, although requirements are a bit more relaxed for plantains.
Great care during handling is needed at all times. Bruising of the pulp is undesirable and cannot always be detected from damage to the peel. RH levels < 85 to 90% accentuate symptoms of mechanical damage.
3. Disorders of Grapes and Its Control:
Of physiological disorders, uneven ripening, post-harvest berry drop, flower- bud and flower drip and pink berry formation are major ones.
i. Uneven Ripening:
Presence of green berries in a ripe bunch of coloured grapes is called uneven ripening. It is a varietal character and a problem in Bangalore Blue, Bangalore Purple, Beauty Seedless and Gulabi grapes. Within a variety this problem varies from bunch-to-bunch.
Generally, inadequate leaf area and non-availability of reserves to a developing bunch is the reason. Cultural practices like cluster thinning, girdling and use of growth regulators can reduce uneven ripening. Application of Ethephon (250 ppm) at colourbreak stage is recommended to reduce the problem.
ii. Postharvest Berry Drop:
This is due to weak pedicel attachment to the berries. This is common in Anab- e-Shahi, Cheema Sahebi and Beauty Seedless. Spraying of NAA (50 ppm), a week prior to harvesting can minimize the post-harvest berry drop.
iii. Flower-Bud and Flower Drop:
When panicles are fully expanded, the flower-buds drop before the fruit set. This is common in north India but not in the south. The reasons for this disorder are not known. Stem girdling about 10 days prior to full bloom can reduce the problem.
iv. Pink Berry Formation:
It is a common disorder in Thompson Seedless and its clone Tas-A-Ganesh in Maharashtra. Pink blush develops on a few ripe berries close to harvesting. The pink colour turns to dull red colour and the berries become soft and watery. They do not stand for long after harvesting. Although the definite cause of the disorder is not known, it is recommended to spray a mixture of 0.2% ascorbic acid and 0.25% sodium diethyl dithiocarbamate at fortnightly intervals commencing berry softening.
4. Disorders of Lemon and Its Control:
Stylar-end breakdown can be a significant problem with lemons. Stylar-end breakdown begins as an apparent breakdown of tissues at the stylar end of the fruit. Typically the stylar-end takes on a wet appearance. Large, mature fruit are more susceptible. The incidence of the disorder can be aggravated by high field heat and rough handling.
Exposing lemons to temperatures below the optimum storage temperature can result in chilling injury. Chilling injury is characterized by peel pitting. Oleocellosis can develop on the peel if hand harvest begins early in the morning or immediately after rainfall when the peel is turgid.
i. Chilling Injury:
Symptoms include pitting, and brown discoloration. Pits Disorders may coalesce and form leathery, brown, sunken areas on the rind. Severity increases with lower temperature below 10°C (50°F) and longer durations of exposure to these temperatures.
ii. Oil Spotting (Oleocellosis):
Harvesting and handling turgid lemons may result in breakage of oil cells in the flavedo and release of the oil that damages surrounding tissues.
iii. Stylar-End Breakdown:
This disorder results from rough handling during harvesting and handling. Its severity varies among cultivars and harvest seasons.
iv. Fruit Cracking:
It is associated with sudden changes in weather conditions, heavy irrigation or rainfall after a prolonged drought and infection of bacteria. Sometimes hot winds also cause fruit cracking.
v. Splitting:
It may be radial (longitudinal) or trans-verse, radial being more common. Lemons are more prone to fruit cracking. It can be minimized by giving timely and frequent light irrigations during summers. Irrigation after a drought should be light. Application of K also reduces fruit splitting.
Postharvest Pathology and Control of Lemon:
Key lemon is very susceptible to stem-end rot caused by Diplodia natalensis and anthracnose (Colletotricum). Stem-end rots caused by D. natalensis, Phomopsis citri, and Alternaria citri are important postharvest diseases in Persian lemon.
In addition, green and blue mold (Penicillium digitatum and P. italicum, respectively) can enter through wounds made during harvesting and handling and appear in storage. Careful handling to minimize mechanical damage can help to reduce blue and green mold. Proper sanitation of packing line equipment and use of postharvest fungicides aid in reduction of post-harvest diseases.
Important diseases are Green mold (Penicillium digitatum), Blue mold (Penicillium italicum), Stem-end rot (Lasiodiplodia theobromae), Phomopsis stem- end rot (Phomopsis citri) and Alternaria stem-end rot (Alternaria citri).
Control Strategies:
1. Minimizing abrasions, cuts, and bruises during handling.
2. Treating lemons before harvest with gibberellic acid to delay senescence.
3. Dipping in hot water (50-53 °C= 120-125°F) for 2-3 minutes.
4. Using chlorine in wash water, postharvest fungicides, and or biological antagonists.
5. Cooling to optimum temperature and subsequent maintenance of optimum temperature and relative humidity.
6. Avoiding exposure to ethylene.
5. Disorders of Guava and Its Control:
Post-harvest desiccation is a major problem along with mechanical injury. Desiccation leads to a dull yellow sometimes wrinkled skin, while mechanical injury leads to browning that can extend into the flesh. Mechanically injured areas of the skin and flesh are very susceptible to decay.
i. Chilling Injury:
Symptoms include failure of mature-green or partially-ripe guavas to ripen, browning of the flesh and, in severe cases, the skin, and increased decay incidence and severity upon transfer to higher temperatures. Fully-ripe guavas are less sensitive to chilling injury than mature-green guavas and may be kept for up to a week at 5°C (41 °F) without exhibiting chilling injury symptoms.
ii. External (Skin) and Internal (Flesh) Browning:
Guavas are sensitive to physical damage during harvesting and handling all the way to the consumer. Symptoms include skin abrasions and browning of bruised areas.
iii. Sun Scald:
Guavas exposed to direct sun light may be scalded. In some countries, paper bags are used to cover guava fruits and protect them from solar radiation and insect infestation while on the tree.
Most diseases problem have pre-harvest origins and are sometimes latent infections such as anthracnose (Colletrotrichium gloeosporioides). Other diseases are associated with insect stings or mechanical damage, for example, Aspergillus rot (Aspergillus niger), Mucor rot (Mucor hyemalis), Phomopsis rot (Phomopsis destructum) and Rhizopus rot (Rhizopus stolonifer). Orchard sanitation and effective postharvest management, such as avoiding mechanical injury and prompt cooling, reduces incidence.
Disease control strategies include good orchard sanitation, effective pre-harvest management to reduce infection, careful handling to reduce physical damage, prompt cooling to 10°C (50 °F) and subsequent maintenance of that temperature throughout the handling system.
iv. Guava Wilt:
Guava plants are attacked by wilt, which along causes heavy losses. It is very difficult to find out an orchard of guava more than 30 years in age because most of its plants die at about 20 years of age due to wilt. Various fungi causing wilt are Fusarium roseum oxysporum f. psidii, F. solani, macrophomina phaseolina and Gliocladium roseum. Resistant rootstocks are the only solution. The planting material should not be obtained from a wilt-infected region or nursery.
Insect Control:
Guavas are a preferred host for fruit flies and must be treated for disinfestation to be accepted in many countries. One of the insect control treatments is heat either as immersion in 46°C-water for 35 minutes or exposed to hot air at 48 °C for 60 minutes. Another potential insect control treatment is irradiation at 0.15-0.30 kGy.
6. Disorders of Apples and Its Control:
Physiological Disorders:
A wide variety of physiological disorders are found in apple fruit, but susceptibility varies by variety, pre-harvest factors and postharvest conditions.
Disorders can be considered in three categories:
Disorders that develop only on the tree. The most important of these is water-core in which intercellular air spaces in the core and cortical tissues become filled with liquid, predominantly sorbitol.
Usually the occurrence of water-core is associated with advancing fruit maturity and low night temperatures prior to harvest, but a variant of the disorder can occur as a result of heat stress. Presence of water-core in fruit at harvest creates problems in certain varieties such as ‘Delicious’ because fruit with moderate or severe water-core can develop breakdown during storage.
By comparison, grade standards for ‘Fuji’ have recently been modified so that water-core in ‘Fuji’ apples is not a grade defect in the U.S. or Canada because water-core is a desirable feature for this cultivar due to the sweetness it imparts to the fruit. Mild or moderate water-core should not be a problem in storage of ‘Fuji’ if fruit are cooled prior to reduction of O2. Severely water-cored fruit should not be placed in CA since breakdown will develop over time.
Disorders that develop on the tree and during storage. Bitter pit is a disorder characterized by development of discrete pitting of the cortical flesh, the pits being brown and becoming desiccated with time. The pits may occur predominantly near the surface or deep in the cortical tissue. An associated disorder, known as lenticel blotch, is also observed in some varieties.
The incidence and severity of bitter pit are affected by variety, but within a variety bitter pit is related to harvest date and climate; in susceptible varieties, harvest of less mature fruit can result in higher bitter pit incidence, as can excessive pruning or high temperatures and/or droughty conditions during the growing season. Effects of climatic conditions are at least partly related to low calcium concentrations in the fruit.
Development of bitter pit during storage results in financial loss and a number of strategies have been employed to prevent its occurrence. These include prediction of risk based on mineral (mainly low calcium) content at harvest or infusion of magnesium.
Rapid cooling, CA storage, and application of postharvest calcium drenches may be able to reduce its occurrence. Recommended rates for application of calcium vary by variety and region; product labels should be followed in conjunction with advice of the local extension specialist. Pre-harvest applications of calcium may be far more effective than postharvest drenching as a means for increasing the concentration of fruit calcium and reducing bitter pit.
i. Disorders that Develop during Storage:
These can be divided into senescent breakdown disorders, chilling disorders and disorders associated with inappropriate atmospheres during storage. Senescent breakdown incidence is related to harvest of over mature fruit and/or fruit with low calcium content. It can be exacerbated by storing fruit at higher than optimal temperatures.
Fruit of susceptible varieties are commonly drenched with calcium before storage, but incidence of senescent breakdown can also be reduced by harvesting fruit at a less mature stage, rapid cooling and reducing storage duration. The most common disorders associated with temperature and atmospheres are superficial scald, soft scald, low temperature breakdown, brown core, internal browning, low O2 injury, and high CO2 injury.
Superficial scald (storage scald) is a physiological disorder associated with long-term storage. It was the major cause of apple fruit loss until the advent of postharvest DPA treatments. Variety, climate, and harvest date affect susceptibility of fruit to the disorder, and decisions about treatment with DPA should be made after consultation with a local extension specialist.
DPA is usually applied with a fungicide to reduce decay incidence, and calcium salts may also be included at the same time to reduce bitter pit or senescent breakdown. Application of label rates of clean DPA should prevent DPA-induced fruit damage and exceeding residue tolerances.
The risk of DPA damage to fruit increases if DPA is not discarded when soil accumulates in the solution. Both DPA use and DPA residues on fruit are prohibited in some countries. Another antioxidant, ethoxyquin, is no longer permitted for use on apples.
Low levels of O2 in CA storage reduce the risk of scald developing and also may permit use of lower DPA concentrations. Alternative ways of controlling superficial scald are being investigated, and storage operators are reducing use of DPA where possible.
Low O2 and low ethylene CA storage also reduce scald incidence. In British Columbia, Canada, 0.7% O2 storage is used as a substitute for DPA treatment. This technique cannot be used universally because fruit grown in other regions may be susceptible to low O2 injury or the risk of scald may be greater due to climate or variety.
Soft scald is characterized by irregular but sharply defined areas of soft, light brown tissue that may extend into the cortex. Susceptibility of fruit to soft scald is variety- and climate-related, but effects of harvest maturity are inconclusive. Over-maturity is almost always a contributing factor in ‘Golden Delicious.’
Storing fruit at 3 °C rather than at lower temperatures can sometimes control the disorder, and DPA used for control of superficial scald may also reduce incidence of soft scald. Storage at a lower temperature following prompt cooling can reduce the incidence of soft scald on ‘Golden Delicious.’
iii. Chilling-Related Disorders:
Low temperature breakdown, brown core and internal browning are affected by variety sensitivity to low temperatures and generally increase in incidence and severity as the length of storage is increased. Climate affects sensitivity of fruit to the disorders, with more problems occurring after colder, wetter growing seasons.
Low temperature breakdown is characterized by markedly brown vascular bundles, browning of flesh, and a clear halo of unaffected tissue underneath the skin. In contrast to senescent breakdown, the affected tissues are more likely to be firmer, more moist, and darker in color.
Brown core (syn. Core-flush) involves browning of the flesh, initially in the core area and later in the cortex, where it becomes difficult to distinguish from low temperature breakdown. Internal browning does not involve breakdown of the flesh, but rather a graying of flesh apparent when apples are cut. Internal browning and core-flush are often associated with higher CO2, since both can occur in CA when CO2 is higher than O2.
Low O2 injury affects fruit in a number of ways. The first indication of injury is loss of flavor, followed by fermentation-related odors. These odors may disappear if storage problems are identified soon enough and severe injury has not occurred.
Injury symptoms range from purpling or browning of the skin in a red colored variety, to development of brown soft patches resembling soft scald, to abnormal softening and splitting of fruit. Varieties vary greatly in response to low O2, and susceptibility to injury is influenced by a number of pre-harvest and postharvest factors.
CO2 injury may be external or internal. The external form consists of wrinkled, depressed colorless or colored areas restricted to the skin surface and usually on the greener side of the fruit. Internal forms are expressed as brown heart and/or cavities in the flesh. Recent studies have shown that DPA can reduce incidence of both external and internal CO2 injuries.
7. Disorders of Litchi and Its Control:
1. Pericarp Browning:
Water loss (desiccation) of litchi results in brown spots on the bright-red shell (pericarp). Under severe conditions or prolonged exposure, the spots enlarge and coalesce until the surface is completely brown. The flavor of the arils within browned fruit may or may not be adversely affected. Packaging in polymeric films reduces water loss and browning severity.
Symptoms include pericarp browning (similar to that caused by water loss) and increased susceptibility to decay. Storage at 1 °C for 12 days before transfer to 20 ° C for one day resulted in pericarp browning.
Fruit cracking in litchi is also favoured if temperature goes above 38 °C and relative humidity less than 60%. Incidence and severity of cracking depend on cultivar and desiccation during storage. Cracks provide an entry way for decay- causing pathogens. Although effective control measures have not been recommended, frequent and adequate irrigation to bearing trees during fruit growth and development period is most useful.
Growth regulators NAA (20 mg/litre of water), GA (40 mg/liter of water), 2, 4-D (10 mg/liter of water), 2, 4, 5-T (10 mg/liter of water) and Ethephon (10 mg/litre of water) reduce the incidence of fruit cracking. Spraying with ZnSO4 (1.5%) weekly or CaNO3 (1.5%) fortnightly from pea-size to harvesting of fruit is and effective method to reduce cracking incidence.
Prolonged storage and over maturity may cause aril breakdown (softening, loss of turgidity, translucency) and loss of flavor beginning at the blossom end and spreading to the stem end.
Decay-inducing pathogens include Alternaria sp., Aspergillus sp„ Botryodiplodia sp., Colletotrichum sp. and various yeasts. Decay control can be achieved by reducing physical injuries to fruits and by prompt cooling and maintenance of the optimum temperature and relative humidity during Litchi marketing. Other decay control treatments under consideration include use of a 10-15% CO2-enriched atmosphere and biological control.
Irradiation at 0.3 kGy can be used for insect disinfestation purposes with no adverse effects on Litchi quality. Exposure to heat at 45 °C for 30 minutes can be used to control some insects on Litchi fruits. Higher temperatures and/or longer exposures to heat damage the fruit. Cold treatment (14 days at 1°C) may induce chilling injury (pericarp browning) in some cultivars.
8. Disorders of Papaya and Its Control:
1. Skin Abrasions:
It results in blotchy coloration such as green islands (areas of skin that remain green and sunken when the fruit is fully-ripe) and accelerate water loss. Abrasion and puncture injuries are more important than impact injury for papayas.
The symptoms include pitting, blotchy coloration, uneven ripening, skin scald, hard core (hard areas in the flesh around the vascular bundles), water soaking of tissues, and increased susceptibility to decay.
Increased Alternaria rot was observed in mature-green papayas kept for 4 days at 2°C, 6 days at 5°C, 10 days at 7.5°C, or 14 days at 10°C. Susceptibility to chilling injury varies among cultivars and is greater in mature- green than ripe papayas (10 vs. 17 days at 2°C; 20 vs. 26 days at 7.5 °C).
Exposure of papayas to temperatures above 30 °C (86 °F) for longer than 10 days or to temperature-time combinations beyond those needed for decay and/or insect control result in heat injury (uneven ripening, blotchy ripening, poor color, abnormal softening, surface pitting, accelerated decay). Quick cooling to 13 °C (55 °F) after heat treatments minimizes heat injury.
Heat Treatments for Insect Control:
1. Hot water treatment – 30 minutes at 42 °C followed within 3 minutes by a 49 °C dip for 20 minutes.
2. Vapor heat treatment – Fruit temperature is raised by saturated water vapor at 44.4 °C until the center of the fruit reaches that temperature, and then held for 8.5 hours.
3. Forced hot air treatment – 2 hours at 43°C (109.4°F) + 2 hours at 45°C + 2 hours at 46.5 °C + 2 hours at 49 °C.
Most serious disease is the mosaic virus, on plant and fruit. It is common in Florida, Cuba, Puerto Rico, Trinidad. It is transmitted mechanically or by the green peach aphid, Myzus Persicae, and other aphids including the green citrus aphid, Aphis spiraecola.
Two forms of mosaic virus are reported in Puerto Rico – the long-known southern coast papaya mosaic virus, the symptoms of which include extreme leaf deformation, and the relatively recent Isabela mosaic virus on the northern coast which is similar but without leaf distortion.
Both forms occur in some north coast plantations. There is no remedy, but measures to avoid spread include the destruction of affected plants, control of aphids by pesticides, and elimination of all members of the Cucurbitaceae from the vicinity. Mosaic is sporadic and scattered and not of great concern in Queensland.
Mosaic and ring-spot viruses are the main limiting factors in papaya production in the Cauca Valley of Colombia.
Bunchy top is a common, controllable mycoplasma disease transmitted by a leafhopper, Empoasca papayae in Puerto Rico, the Dominican Republic, Haiti, and Jamaica; by that species and E. dilitara in Cuba; and by E. stevensi in Trinidad. Bunchy top can be distinguished from boron deficiency by the fact that the tops of affected plants do not ooze latex when pricked.
In the subtropical part of Queensland papaya plants are subject to die- back, a malady of unknown origin, which begins with shortening of the petioles and bunching of inner crown leaves.
i. Alternaria Rot:
It is caused by Alternaria alternata follows chilling injury of papayas kept at temperatures below -12°C (54°F).
ii. Anthracnose:
It is caused by Colletotrichum gloesporioides, is a major cause of postharvest losses. Latent infections of unripe papayas develop as the fruits ripen. Lesions appear as small, brown, superficial, water soaked lesions that may enlarge to 2.5 cm (1 inch) or more in diameter. It is controllable by spraying every 10 days, or every week in hot, humid seasons, and hot water treatment of harvested fruits.
A strain of this fungus produces “chocolate spot” (small, angular, superficial lesions). A disease resembling anthracnose but which attacks papayas just beginning to ripen, was reported from the Philippines in 1974 and the causal agent was identified as Fusarium solani.
iii. Black Spot:
It results from infection by Cercospora papayae, has plagued Hawaiian growers since the winter of 1952-53. It causes defoliation, reduces yield, blemishes the fruit, and is unaffected by the hot-water dip. It can be prevented by field use of fungicides.
iv. Black Stem-End Rot:
It is caused by Phoma caricae-papayae attacks fruit pedicel. After harvest, the disease lesion on fruits appear in the stem area which becomes dark-brown to black. Another stem-end rot is caused by Lasiodiplodia theobromae.
v. Damping-Off:
Young papaya seedlings are highly susceptible to damping- off, a disease caused by soil-borne fungi Pythium aphanidermatum, P. ultimum, Phytophthorap palmivora, and Rhizoctonia sp., especially in warm, humid weather. Pre-planting treatment of the soil is the only means of prevention.
vi. Phomopsis Rot:
It is caused by Phomopsis caricae-papayae begins in the stem end or a fruit skin wound and can develop rapidly in ripe fruits; invaded tissue softens and darkens slightly.
General Control Strategies:
(1) Careful handling to minimize mechanical injuries,
(2) Prompt cooling and maintenance of optimum temperature and relative humidity throughout postharvest handling operations,
(3) Application of fungicides, such as thiabendazole (TBZ), and
(4) Dipping in hot water at 49 °C for 20 minutes.
9. Disorders of Fig and Its Control:
Physiological Disorder:
Fig is susceptible to sun-burn, fruit splitting and fruit drop. Sun-burn is noticed mostly in young plants and those subjected to excessive pruning. The trunk and shoots that are exposed to direct sun are prone to sun-burn. The affected parts crack and the bark peels off, providing easy access for fungi and other infection.
Developing a good canopy by proper pruning and coating the exposed limbs with lime protect the plants from sunburn. Fruit splitting is attributed to sudden change in atmospheric humidity during ripening. This makes the fruit unfit for consumption as the pulp is exposed to insert and microbial infection. Fruit drop may result from excessive drought and heat, cold nights or light frost. Lack of pollination also causes fruit drop in figs.
CA-Related Disorders:
Extended storage in CA can result in loss of characteristic flavor. Figs exposed to less than 2% oxygen and/or more than 25% carbon dioxide develops off- flavors due to fermentative metabolism. Extended storage in CA can result in loss of characteristic flavor. Figs exposed to < 2% O2 and/or > 25% CO2 develops off-flavors due to fermentative metabolism.
Postharvest Pathology:
Alternaria rot, caused by Alternaria tenuis appears as small, round, brown-to- black spots over the fruit surface. Any cracks on the skin make the fruit more susceptible to the rot.
Black mold rot, caused by Aspergillus niger, appears as dark or yellowish spots in the flesh with no external symptoms. At advanced stages the skin and flesh turn slightly pink color and white mycelia with black spore masses follow. Handling figs to avoid infection with Aspergillus species is very important to minimize formation of mycotoxins. Solar heating reduces insect infestations in ripening and drying figs.
Endosepsis (soft rot), caused by Fusarium moniliforms, appears in the cavity of the fig making the pulp soft, watery and brown with sometimes an offensive odor.
Souring is a pre-harvest problem resulting from yeasts and bacteria carried into figs by insects, especially vinegar flies, resulting in odors of alcohol or acetic acid.
Recommendations to reduce postharvest diseases are the following:
1. Controlling orchard insects to reduce fruit damage and transmission of fungi.
2. Using effective control of pre-harvest diseases.
3. Enforcing strict sanitation of picking and transporting containers; supervising careful handling to minimize abrasions, cracks, and other physical damage; avoiding picking figs for fresh market from the ground, enforcing prompt cooling to 0 °C (32 °F) and; maintaining the cold chain all the way to the consumer.
Fig trees are prone to attack by nematodes (especially Meloidogyne spp.) and, in the tropics, have been traditionally planted close to a wall or building so that the roots can go underneath and escape damage. A heavy mulch will serve equally well. Today, control is possible with proper application of nematicides.
In India, a stem-borer, Batocera rufomaculata, feeds on the branches and may kill the tree. Lepidopterous pests in Venezuela include the fig borer, Azochis gripusalis, the larvae of which feed on the new growth, tunnel down through the trees to the roots and kill the tree. Another, called cachudo de la higuera, has prominently horned larvae up to 3 1/8 in (8 cm) long that can destroy a fig tree in a few days.
There are also coleopterous insects of the genera Epitrix and Colaspis that perforate and severely damage the leaves and shoots. Scale insects include Asterolecanium sp. which attacks the bark of trees weakened by excessive humidity or prolonged drought, and the lesser enemy, Saissetia haemispherica.
A common and widespread problem is leaf rust caused by Cerotelium fici; bringing about premature leaf fall and reducing yields. It is most prevalent in rainy seasons. Leaf spot results from infection by Cylindrocladium scoparium or Cercospora fici. Fig mosaic is caused by a virus and is incurable. Affected trees must be destroyed.
10. Disorders of Pear and Its Control:
1. Senescent Scald:
Dark-brown skin discoloration begins as small spots and develops into large areas of skin turning brown after long term storage; brown skin may slough off. Prompt cooling and maintenance of optimum fruit temperature minimize this disorder. It occurs when fruit become senescent.
Diffuse brown skin discoloration occurs after several months of storage and during ripening after storage. Scald inhibitors, such as ethoxyquin, may be used on pears that are stored longer than 3 months. Controlled-atmosphere storage delays scald incidence and severity.
Translucent, water-soaked appearance of tissue while frozen. Upon thawing tissue turns brown and soft. Severe freezing causes cavities in the cortex. Freezing temperatures depend upon soluble solids content of pears.
4. Bitter Pit (Cork Spot, Anjou Pit):
Brown, corky lesions appear in the flesh, mainly toward the calyx end. An uneven surface with darker colored depressions indicates pitted tissue. High rates of nitrogen application increase the incidence of bitter pit while calcium sprays before harvest decrease its occurrence.
Browning of interior walls of carples and adjacent core tissue; in severe cases cortex tissue turns light brown and cavities may develop in damaged tissue. Susceptibility of pears to CO2 injury increases with advanced maturity, delayed cooling, prolonged storage, and low O2 levels during storage.
Core browning and accumulation of fermentation volatiles (ethanol, acetaldehyde, and ethyl acetate). More mature pears are more susceptible to low O2 injury.
Control Strategies:
1. Effective pre-harvest disease control procedures;
2. Careful handling during harvesting and postharvest preparation for market to minimize mechanical injuries;
3. Prompt cooling to 0° C;
4. Maintenance of proper temperature (-1 to 0°C) during storage and transport;
5. Use of postharvest chemical treatments (sodium orthophenyl phenate or chlorine added to the dump tank water; thiabendazole applied in a line spray after sorting;
6. Use of CA storage.
11. Disorders of Plum and Its Control:
1. Physiological Disorders:
Internal Breakdown or Chilling Injury:
This physiological problem is characterized by flesh translucency, flesh internal browning, flesh mealiness, flesh bleeding, failure to ripen and flavor loss. These symptoms develop in plum and fresh prunes during ripening after a cold storage period. Thus, these symptoms are usually detected by consumers. Fruit stored within the “killing temperature range” 2-8°C (36-46°F) are more susceptible to this problem.
2. Pathological Disorders:
i. Brown Rot:
Caused by Monilia fructicola is the most important postharvest disease of stone fruits. Infection begins during flowering and fruit rot may occur before harvest but often occurs postharvest. Orchard sanitation to minimize infection sources, pre-harvest fungicide application and prompt cooling after harvest are among the control strategies. Also, postharvest fungicide treatment may be used.
ii. Gray Mold:
Caused by Boyrytis cinerea can be serious during wet spring weather. It can occur during storage if the fruit has been contaminated through harvest and handling wounds. Avoiding mechanical injuries and good temperature management are effective control measures.
iii. Rhizopus Rot:
Caused by Rhizopus stolonifer can occur in ripe or near ripe stone fruits kept at 20 to 25°C (68 to 77° F). Cooling the fruits and keeping them below 5°C (41 °F) is very effective against this fungus.
12. Disorders of Peach and Its Control:
Physiological Disorders:
1. Internal Breakdown or Chilling Injury:
This physiological problem is characterized by flesh internal browning, flesh mealiness, flesh bleeding, failure to ripen and flavor loss. These symptoms develop during ripening after a cold storage period, thus, are usually detected by consumers. Fruit stored within the 2.2-7.6°C temperature range are more susceptible to this disorder.
2. Inking (Black Staining):
It is a cosmetic problem affecting only the skin of peaches and nectarines. It is characterized by black or brown spots or stripes. These symptoms appear generally 24-48 hours after harvest. Inking occurs as a result of abrasion damage in combination with heavy metals (iron, copper and aluminum) contamination. This occurs usually during the harvesting and hauling operations, although it may occur in other steps during postharvest handling.
Gentle fruit handling, short hauling, avoiding any foliar nutrient sprays within 15 days before harvest, and following the suggested pre-harvest fungicide spray interval guidelines are our recommendations to reduce inking in California.
3. Sunscald:
Peach trees are affected with sunscald. It is a severe damage to the exposed trunk and main scaffold branches. Shading of branches considerably reduces the incidence. To overcome this problem, painting of exposed surface with lime paste and shading by wrapping straw or hay around the trunk and thicker branches is quite effective in mitigating the problem.
5. Splitting of Fruits:
The fruits are affected on dorsal and ventral sides mostly at the time of pit hardening stage. Sometimes gum exudes for the fruit making it unfit for consumption. Splitting and gumming are accentuated during heavy rains after a long dry spell. The exact cause of this problem is still unknown.
Pathological Disorders:
1. Brown Rot:
Caused by Monilia fructicola is the most important postharvest disease of stone fruits. Infection begins during flowering and fruit rot may occur before harvest but often occurs postharvest. Orchard sanitation to minimize infection sources, pre-harvest fungicide application, and prompt cooling after harvest are among the control strategies. Also, postharvest fungicide treatment may be used.
2. Gray Mold:
Caused by Boyrytis cinerea can be serious during wet spring weather. It can occur during storage if the fruit has been contaminated through harvest and handling wounds. Avoiding mechanical injuries and good temperature management are effective control measures.
3. Rhizopus Rot:
Caused by Rhizopus stolonifer can occur in ripe or near ripe stone fruits kept at 20 to 25 °C. Cooling the fruits and keeping them below 5°C is very effective against this fungus.