Common Physiological Disorders in Tropical and Sub-tropical Produce

Tropical and sub-tropical fruits are prized worldwide for their vibrant flavours, rich nutrition, and growing export value. But here’s the challenge – these fruits are extremely sensitive to their storage environment. When stored below 10°C, many of them develop what are known as physiological disorders. These are not caused by pathogens or pests. Instead, they arise from internal metabolic imbalances triggered by improper temperature, mineral deficiency, or gas composition during storage. Understanding these disorders is essential for anyone involved in postharvest handling, cold chain management, or food quality assurance.

What are physiological disorders in produce? 🔗

Physiological disorders are abnormal conditions in fruits and vegetables that result from disruptions in normal metabolic processes. Unlike diseases caused by fungi or bacteria, these disorders stem from factors like extreme temperatures, nutrient imbalances, and poor atmospheric composition during storage. According to research published by the International Journal of Agriculture, Environment and Biotechnology, adverse environmental conditions such as high or low temperature, moisture content, and nutritional or hormonal imbalance are the primary causes of physiological disorders in tropical and sub-tropical fruits.

These disorders are especially problematic for fruits like mango, banana, citrus, papaya, litchi, and guava – crops that form the backbone of tropical horticulture and international fruit trade. Post-harvest losses due to these conditions can be economically devastating, particularly in developing countries where cold chain infrastructure is still evolving.

Superficial scald 🔗

Superficial scald is one of the most well-documented storage disorders, particularly in apples and pears. It appears as irregular, diffuse patches of brown to dark brown or black discolouration on the skin surface. Symptoms typically develop after the fruit has been in cold storage for several months and intensify once the produce is removed to warmer temperatures.

The root cause is linked to α-farnesene, a volatile hydrocarbon that accumulates in the fruit’s wax layer during cold storage. When this compound oxidises, it produces conjugated trienols and other by-products that damage skin cells, leading to the brown patches. As explained by Washington State University’s tree fruit programme, ethylene promotes α-farnesene production, which is why immature fruit – which tend to produce more ethylene in storage – are more vulnerable.

Several factors increase scald risk: harvesting the fruit when physiologically immature, high nitrogen and low calcium content, hot and dry weather before harvest, and poor ventilation in cold storage rooms. Cultivars like Granny Smith and Red Delicious are highly susceptible. Management strategies include post-harvest antioxidant treatment with diphenylamine (DPA), application of 1-methylcyclopropene (1-MCP) before cool storage, and ultra-low oxygen storage environments.

Carbon dioxide injury 🔗

When fruits are kept in controlled atmosphere (CA) storage with elevated carbon dioxide (CO₂) levels or excessively low oxygen, they can develop CO₂ injury. This disorder manifests both externally and internally. On the surface, you may see brown, sunken lesions that can merge into large patches. Internally, discoloured areas form within the vascular bundles, sometimes creating dry cavities in the flesh. A strong fermentation odour may also be noticeable.

According to the University of Maryland Extension, CO₂ injury in apples is caused when carbon dioxide exceeds about 0.5% and oxygen drops below 1.5% during controlled atmosphere storage. The disorder develops early in the storage period and grows more severe as storage continues.

Prevention requires careful monitoring of atmospheric gas concentrations. Delaying the onset of controlled atmosphere conditions, maintaining low CO₂ levels during early storage, and applying DPA can help reduce incidence. This disorder is particularly common in cultivars such as Braeburn, Fuji, and Honeycrisp.

Core flush 🔗

Core flush refers to a browning of the internal flesh tissues around the core of the fruit. It is most commonly observed in apples after extended cold storage at around 0°C. The affected tissue around the core turns brown and may develop a waterlogged or soft texture.

One contributing factor appears to be restricted oxygen supply to the core. According to the Plants in Action resource from the Australian Society of Plant Scientists, conditions that potentially cause anaerobiosis – such as large fruit size, an airtight calyx, and low-oxygen atmospheres – increase the incidence of core flush. It is essentially a form of senescent breakdown in which the innermost tissues degrade before the outer flesh.

The disorder can be significantly reduced by storing fruit at slightly warmer temperatures (around 3-4°C instead of 0°C) and maintaining proper oxygen levels in controlled atmosphere storage. The cultivar ‘McIntosh’ is especially prone to this condition.

Low temperature breakdown (chilling injury) 🔗

Low temperature breakdown, commonly referred to as chilling injury (CI), is one of the most serious physiological disorders affecting tropical and sub-tropical produce during cold storage. It occurs when fruits are stored at temperatures above their freezing point but below their critical chilling threshold – typically below 10-13°C for tropical species and below 5-8°C for sub-tropical ones.

The symptoms are wide-ranging and include surface pitting, peel browning, internal discolouration, water-soaked lesions, failure to ripen, off-flavour development, and increased susceptibility to decay. Research published in Frontiers in Plant Science notes that chilling injury causes peel softening, surface depression, aroma deterioration, and abnormal ripening in cold-sensitive solanaceous vegetables and tropical fruits alike.

At the cellular level, low temperatures disrupt normal membrane function. The lipid bilayer of cell membranes transitions from a fluid to a gel-like state, making it less permeable and causing cellular contents to leak. This triggers a cascade of effects – increased ethylene production, elevated respiration rates, enzyme inactivation, and the accumulation of reactive oxygen species.

Which fruits are most vulnerable? 🔗

Bananas, mangoes, papayas, avocados, pineapples, and citrus fruits are all highly susceptible. For instance, bananas show peel browning and failure to ripen when stored below 12°C, while mangoes develop skin pitting and internal browning below 10°C. The severity of chilling injury depends on the storage duration, the specific temperature, the cultivar, and the maturity of the fruit at harvest.

How can chilling injury be managed? 🔗

Several strategies help reduce CI: temperature conditioning (exposing fruit to moderately low temperatures before actual cold storage), intermittent warming (briefly raising temperatures during storage), wax or edible coatings, modified and controlled atmosphere storage, and chemical treatments such as methyl jasmonate and salicylic acid. According to a comprehensive review in Trends in Food Science & Technology, these postharvest technologies work by maintaining membrane integrity, enhancing antioxidant systems, and regulating ethylene metabolism.

Senescent breakdown 🔗

Senescent breakdown occurs when fruit tissues naturally deteriorate as the produce ages, regardless of whether storage conditions are ideal. It represents the final stage in the fruit’s biological life – the transition from ripening to death. The tissues become mealy, soft, and develop internal browning. Flavour becomes flat and unappealing.

This disorder is more common in fruit that has been stored for extended periods or was harvested at an overripe stage. According to the Pacific Northwest Pest Management Handbook, soggy breakdown – a related condition in apples – involves internal browning triggered by very low storage temperatures and is especially problematic in cultivars like Honeycrisp.

While senescent breakdown cannot be completely prevented (it is, after all, a natural process), it can be delayed. Harvesting at optimal maturity, rapid cooling after harvest, and appropriate storage temperatures and atmospheres are the primary tools. The use of 1-MCP, which blocks ethylene receptors and slows ripening, has also proven effective in delaying senescence.

Water core 🔗

Water core is an internal disorder commonly seen in apples (especially the Fuji variety) where areas of the flesh appear waterlogged, glassy, and translucent. These water-soaked zones typically develop around the vascular bundles near the core. In mild cases, the condition may not be visible externally at all – you only see it when you cut the fruit open.

The disorder is caused by a breakdown in sorbitol transport across cell membranes. Sorbitol, a sugar alcohol, accumulates in intercellular spaces instead of being taken up by cells, drawing water into those spaces. As noted by the National Horticulture Board of India, water core is promoted by a high leaf-to-fruit ratio, elevated nitrogen and boron levels, low calcium, excessive thinning, and exposure to high temperatures. Late-harvested, fully mature fruits are most at risk.

In severe cases, the waterlogged tissue can lead to anaerobic conditions, fermentation odours, and eventually browning similar to core flush. The most effective preventive measure is timely harvesting before the condition develops extensively. Interestingly, mild water core symptoms can sometimes resolve on their own during cold storage as the tissue gradually reabsorbs the excess water.

Bitter pit 🔗

Bitter pit is one of the most economically significant physiological disorders in apple production. It presents as small (2-10 mm), dark, sunken pits on the skin surface, usually concentrated around the calyx end of the fruit. Beneath these pits, the flesh is spongy, dry, and brown. The pitting gives the affected tissue a characteristically bitter taste.

The primary cause is a calcium deficiency in the fruit tissue. Calcium is a critical structural component of cell membranes and cell walls. When fruit calcium levels are low, cells become leaky, lose their integrity, and die – forming the telltale pits. The condition is worsened by high nitrogen, high potassium, and low boron levels in the fruit. Large-sized fruits from lightly cropped trees are particularly susceptible.

Bitter pit can develop on the tree itself, but it more commonly appears during the first one to two months of cold storage. According to the University of Maryland Extension, cultivars like Honeycrisp, Granny Smith, and Golden Delicious are highly prone. Preharvest calcium sprays directly onto developing fruit, proper rootstock selection, balanced nutrition management, and post-harvest calcium dips before storage are the main preventive approaches.

Freezing injury 🔗

Freezing injury is distinct from chilling injury. While chilling injury occurs above the fruit’s freezing point, freezing injury happens when the tissue temperature actually drops below the freezing point of the produce, causing ice crystals to form within the cells. These ice crystals physically rupture cell membranes and walls, leading to irreversible damage.

Once thawed, frozen tissue becomes waterlogged, soft, and translucent. The texture completely collapses, and the affected areas turn brown rapidly. Unlike chilling injury, which may be partially reversible if detected early, freezing injury causes permanent cell destruction.

Freezing injury is a risk when cold storage temperatures are set too low, when there is uneven air circulation within a storage facility (creating cold spots), or during transport in winter conditions. Tropical and sub-tropical fruits, which already have relatively high freezing points compared to temperate produce, are especially vulnerable. Prevention is straightforward: maintain storage temperatures well above the produce’s freezing point, ensure uniform temperature distribution in storage rooms, and use proper insulation and monitoring equipment during transport.

Putting it all together: a quick comparison 🔗

Here is a summary of the key physiological disorders discussed:

Superficial scald – skin browning caused by oxidation of α-farnesene during cold storage; managed with antioxidants and 1-MCP. Carbon dioxide injury – brown sunken lesions and internal cavities from excessive CO₂ in controlled atmosphere storage; managed by monitoring gas levels. Core flush – internal browning around the core linked to oxygen deprivation; reduced by slightly warmer storage temperatures. Low temperature breakdown – broad spectrum of chilling symptoms in tropical produce stored below 10-13°C; managed by temperature conditioning and intermittent warming. Senescent breakdown – natural age-related tissue deterioration; delayed by optimal harvest timing and ethylene management. Water core – glassy, waterlogged flesh caused by disrupted sorbitol transport; prevented by timely harvest. Bitter pit – sunken dark pits from calcium deficiency; controlled through calcium nutrition. Freezing injury – ice crystal damage below the freezing point; prevented by temperature monitoring.

Each disorder has its own unique triggers and symptoms, but they share a common thread: improper postharvest handling is almost always a contributing factor. Whether it is storing mangoes too cold, letting CO₂ build up around apples, or neglecting calcium nutrition in the orchard, these problems are largely preventable with the right knowledge and practices.

What do you think? Given that tropical fruits are increasingly shipped across continents, how can developing countries improve their cold chain infrastructure to reduce these physiological disorders? And in your own experience, have you noticed quality differences in fruits that may have been caused by storage-related issues rather than disease?

References

1. https://www.researchgate.net/publication/312658504_Review_on_Physiological_Disorders_of_Tropical_and_Subtropical_Fruits_Causes_and_Management_Approach
2. https://treefruit.wsu.edu/article/superficial-scald-management-in-apples/
3. https://extension.umd.edu/resource/orchard-cold-storage-closer-look-development-nine-physiological-disorders-apples-fs-2022-0640
4. https://rseco.org/content/1164-storage-disorders.html
5. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1488666/full
6. https://www.sciencedirect.com/science/article/abs/pii/S0924224421003307
7. https://pnwhandbooks.org/plantdisease/host-disease/apple-malus-spp-storage-problems
8. https://nhb.gov.in/pdf/fruits/apple/app003.pdf