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Physiological Disorders

Introduction

The Physiological Disorders section of the card set includes most the common disorders of physiological origins found during the sorting and packing of Washington apples. Bitter pit, scalds and lenticel conditions are just a few of the items presented in this section. The upcoming revision of the Defects & Disorders Guide may include additional forms of physiological disorders such as emerging conditions or reclassified disorders.  To navigate directly to the pest damage of interest use the links below this text block.  The card images shown on this site are slightly modified from their original form to accommodate web formatting. Any reproduction of the card images or content without permission is in violation of WSU Copyright policies.

Bitter pit   Superficial scald   Senescent scald   Core flush   Internal breakdown   Braeburn browning   Watercore   Lenticel breakdown   Lenticel blotch pit   CO2 injury   Chlorine burn   Chilling injury   Humidity disorders

Bitter Pit

Bitter Pit (BP) is a disorder that begins in the orchard and is related to low calcium. Effected  cells gradually die, but fruit may show no sign externally at harvest. Early external symptoms begin as slightly water soaked spots or patches, later developing into darker, sunken spots as the tissue below dies and begins to desiccate. Below the skin, the affected flesh is brown and corky, which distinguishes BP from other disorders. This disorder is easily confused with stinkbug damage or lenticel blotch pit. The symptoms are usually on the lower half of the fruit, unlike stinkbug damage. However, in severe cases the spotting may extend to the upper half as well. 

Figure 1: A Granny Smith showing spots which are larger and more diffuse with irregular edges.
Figure 2: A Golden Delicious with the more common pin-point type spots.

Superficial Scald

Superficial scald is a very common post-harvest disorder. The appearance and severity depend on the susceptibility of the variety with Granny Smith and Red Delicious being among the worst affected. The skin of the affected fruit turns brown in patches, especially on the shaded side and may become rough. Only the surface of the fruit is effected with the flesh remaining firm and of eating quality. The margins between normal and affected skin are diffuse. Browning develops rapidly once the fruit is moved from cold storage to room temperature.

Figure 1: Superficial scald appears as brown rough patches on this Granny Smith apple.

Senescent Scald

Senescent scald appears as brown patches on the skin that may become sunken and rough with distinct margins, often ribbon like. Unlike superficial scald, senescent scald usually appears on the sun exposed side of the fruit and on late harvested fruit. Golden Delicious and late harvested or over-stored fruit may be susceptible to senescent scald. Unlike superficial scald, the interior of the fruit may have brown flesh and have internal breakdown.

Figure 1: Golden Delicious fruit showing senescent scald after cold storage.

Core Flush

Core flush, a form of senescent breakdown is common in Granny Smith, Braeburn and other apple varieties. The core area turns pink then brown. The discoloration starts near the core and extends with wedges of brownish tissue outward. The discoloration may circle the core partly or  completely.  The affected tissue is moist and softer than unaffected tissue. In severe cases it may extend just below the skin. There is no exterior symptom.

Figure 1. Core flesh starts to turn pink.
Figure 2. The pink gradually turns brown.

Internal Breakdown

Over-mature and large fruit are highly susceptible to internal breakdown. Internal breakdown is characterized by flesh browning and breakdown. Internal symptoms may be restricted to one side of the fruit, or involve the entire fruit. Often there is a 1/4 inch ring of healthy flesh surrounding the affected tissue. The sun exposed side or the calyx end is more often affected with the rest of the fruit normal. The skin of affected fruits may be normal, or dull and dark, and in later stages of the disorder it sometimes becomes cracked.

Figure 1. Over-mature Granny Smith apple with extensive internal breakdown with only slight bruise-like discoloration on one side of the outer skin (right side).

Braeburn Browning

The apple variety Braeburn is susceptible to an internal disorder called Braeburn browning disorder (BBD). At harvest, this disorder has the appearance of light to dark brown areas similar in nature to watercore, but occurring without pattern anywhere in the flesh. Symptoms of BBD developing in storage include tissue browning resembling the internal cavities caused by CO2 injury. However, BBD is thought to be related to late harvest. 

Figure 1. Sliced Braeburn apples shows the progression of severity of BBD.

Watercore

Water core appears as water soaked areas of the flesh first associated with vascular bundles. In severe cases, the effected tissue may spread covering large areas of the flesh. In these instances, watercore is externally visible by the appearance of translucent skin blotches on lighter pigmented apples, or as very dark patches on darker fruit. In mild cases, watercore will disappear (sugar re-absorbed) early on during cold storage. However if severe enough, watercore may develop into internal breakdown (watercore breakdown).

Figure 1. A Granny Smith apple showing the clear skin blotches on the slice exposing the water soaked flesh beneath.
Figure 2. When the fruit is cut crosswise a pinwheel pattern of water soaked flesh is exposed. In severe cases, the tissue would turn brown as it breaks down and decays.

Lenticel Breakdown

Lenticel breakdown is a physiological disorder effecting the surface of apples. Before the packing, there is little evidence of a problem; however, within a few days of packing, symptoms appear as dark brown pits in the fruit skin around the lenticels reducing marketable yield. It usually occurs on the less sun exposed side and along color margins. Early symptoms appear as small dimples. As firmness decreases, pits grow in size and depth. The flesh is not deeply effected except for a possible cavity directly under the pits. Lenticel breakdown is easily confused with lenticel blotch pit. A dye test has been developed to help determine fruit susceptibility to this disorder at harvest.

Figure 1. Gala apple showing moderate lenticel breakdown symptoms.

Lenticel Blotch Pit

Lenticel blotch pit is similar in appearance to both lenticel breakdown and bitter pit.  Lenticel blotch pit  has irregular patches around the lenticels, unlike the more defined circles found in lenticel breakdown; and are usually near the calyx end as in bitter pit, or on the more sun exposed side of the fruit. Unlike lenticel breakdown, the flesh browning may extend deeper, as with bitter pit, and will likely increase and deepen after harvest. Hastening ripening will increase symptoms.

Figure 1. Fuji apple showing lenticel blotch pit on the lower half of the fruit.
Figure 2. Cutting through a blotch exposes corky tissue browning similar to bitter pit.

Carbon Dioxide (CO2) Injury

If the carbon dioxide (CO2) level is too high during controlled atmosphere (CA) storage both external and internal injury symptoms may occur. External injury resembles snowflake-like patches which may join to form one very large patch. Internal symptoms appear as discolored areas within the vascular bundles. The tissue may be brown and develop pockets. A noticeable aroma of fermentation may be present when CA storage is opened, or the fruit is cut.

Figure 1. A Golden Delicious apple with external CO2 injury showing irregular (snowflake-like) margins.
Figure 2. Internal CO2 damage with brown flesh and pockets.

Chlorine Burn

Sodium hypochlorite (chlorine bleach) is commonly used in dump tanks as a disinfectant. It is important that the chlorine concentration be monitored. If the concentration is too low the tank water no longer works to disinfect. However, if the concentration is too high the fruit can be burned. 

Figure 1. The stem bowl and calyx are susceptible to burning because they fill with water increasing the exposure time to the chlorine.

Chilling Injury

Fruit stored below their tolerance point may show a variety of symptoms depending on the cultivar, temperature and duration of storage at the adverse temperature. Symptoms may vary from browning of the skin to deep flesh browning and translucency. Dry internal cavities and flesh browning may also develop. Fruit also may have a bitter taste and smell of fermentation upon cutting. 

Figure 1. A Red Delicious apple showing external browning and skin translucency.

Humidity Disorders

Excess or too low humidity can have a detrimental effect on fruit during storage. If the humidity is too high the cells swell and expand to the point where the tissue cracks. Too low humidity causes dehydration of the tissues leading to shriveling.

Figure 1. A Golden Delicious apple showing cracking at the lenticels. If conditions are severe enough the cracks will expand resulting in large deep branching cracks extending across the fruit. Often the cracks will become infected and the fruit will decay.
Figure 2. The Gala shown here was stored at too low relative humidity and became shrivelled.