Melon disorders and diseases
Good quality melons are free from diseases and disorders. Customers are not willing to purchase fruit presenting rots or damaged skin. Furthermore fruit that looks good on the outside but presenting brown flesh will not lead to happy customers. There are dozens of different diseases and disorders, which are not always easy to recognize. A good diagnosis of the fruit’s health is important. By recognizing the symptoms of a disease or disorder, it can be linked to the cause. If you know the cause, you know what measures can be taken to prevent the disease or disorder in the future.
Identification of melon disorders and diseases usually takes place by carefully looking at the symptoms. Some symptoms are visible from the outside, while others can only be found internally after cutting. It is important to detect the quality issues as early as possible in the supply chain to reduce further incidence. Retailers can also benefit from knowledge about disorders they may encounter. For them, it is important to know whether the cause lies in a previous stage in the supply chain or is due to their own operations. Common causes of deterioration of melons are bruises, moulds and rots.
Frequently occurring disorders and diseases
Melon with bruising damage. Photo by WUR
Bruising and injuriesRough handling can easily lead to damage of the melon skin, at any stage of the supply chain. For example, the effect of rough harvesting can manifest itself in bruises and injuries at a later stage. Bruising can also occur due to too tight packaging that causes pressure on the melons. Bruises are usually soft with discoloration of the underlying flesh. These mechanical damages not only make the fruit unattractive, but often also leads to secondary rot development.
Sunken areas in a melon skin which may result from rubbing or injuries. Photo by WUR.
Sunken areasMelons may show slightly sunken areas on the skin that have developed after harvest. These areas are often discolored (dark) and sharply sunken. The spots and the underlying flesh are usually firm. In severe cases, the sunken areas are covered with mold and can develop into decay. The sunken areas may result from rubbing or other injuries. So be careful with melons, in every part of the supply chain.
Too cold temperatures for too long causes chilling injury with melons. Photo by triart / Shutterstock.com
Chilling injuryMelons are sensitive to too low temperatures. Symptoms of chilling injury include pitting or sunken spots on the skin, skin discolourations, pulp water infiltration, off-flavor, and increased susceptibility to decay. This disorder is caused by several days of storage below the optimum temperature which is highly dependent on the melon cultivar. Damage depends further on the duration and depth of the temperature. The longer the period at low temperature and the lower the temperature, the greater the damage. Symptoms appear especially after transfer to higher temperatures.
Overripe melons. Photo by WUR.
SenescenceOverripe fruit can easily deteriorate, it is a consequence of aging. Surface breakdown, softening and off-flavours are part of the deterioration. This last stage of the fruit is called senescence. Senescence is enhanced by higher temperatures. The melons with senescence symptoms may have been stored under suboptimal conditions such as too high temperature or were simply stored for too long.
Melon showing severe symptoms of desiccation. Photo by WUR.
DesiccationMelons have a high water content (90-95%). Some of this water is lost by transpiration but generally the moisture loss of watermelons is low and not critical for quality. However, water loss through punctures or damaged surface netting can be significant. Some shrivelling of the skin can then occure. Desiccation can also lead to loss of glossiness. The risk of shrivelling symptoms increases with lower relative humidity, higher temperature, longer storage time and damage to the skin.
Mould on a melon. Photo by WUR.
MouldsLong periods of high humidity or condensation can stimulate the growth of stem-scar moulds and surface moulds. These moulds can be of a light type, and disappear, for example, after opening the (foil) packaging and exposure to the drier outside air. It does not necessary lead to breakdown of fruit tissue. But if the mould causes tissue to decay, this of course has serious consequences for the marketability of the melon.
Melon with rot problem at the stem end. Photo by WUR
RotsSeveral types of pathological diseases can occur, such as Alternaria, Cladosporium, Geotrichum and Rhizopus. For example, the latter manifests in wounds and bruises. Bacterial rot can be caused by, for example, species of Erwinia, which gain access through insect punctures or other skin injuries. In addition to damage, rot is often also linked to senescence. The development of rot after harvest can often be controlled by quickly cooling and preventing bruising and injuries.