Certain conditions such as nutritional imbalance, production practices, cultivars and storage conditions can predispose apple fruits to different types of physiological disorders which can lead to significant losses in market value. This write up describes storage disorders of apple diagnosed at the MU Plant Diagnostic Clinic.
Bitter pit associated with calcium deficiency is a physiological disorder of apple fruits. Bitter pit begins in the orchard at harvest but symptom does not develop until storage. Depending on the cultivar, the symptoms appear as dark-brown sunken lesions (Figure 1a), approximately 2 to10 mm in diameter on the surface of the fruit but most commonly at the calyx end. The flesh below the skin of infected area when peeled is dark and corky in appearance (Figure 1b). High nitrogen fertility, light crop load and premature fruit harvest are factors that may increase bitter pit incidence. Apple cultivars such as Honeycrisp, Jonagold, Golden Delicious and Granny Smith are more susceptible to bitter pit. Calcium spray in the orchard before harvest and drenching harvested fruits in a calcium solution before storage can help to minimize the incidence of this disorder.
Lenticel breakdown is a physiological disorder most often observed in stored apples. Symptom of lenticel breakdown can be inconspicuous at harvest but may become evident within few days of packing. Initial symptoms develop as small spots over the lenticel on apple skin (Figure 2). As the fruit firmness decreases in storage, these spots enlarge, become sunken, and turn dark brown. Unlike bitter pit, lenticel breakdown appears only on the skin with no corking of the flesh. Mineral imbalance, late fruit harvest, and longer fruit storage are conditions that can increase susceptibility of apple fruit to lenticel breakdown. There is limited information on the management of lenticel breakdown in apples.
Another apple disorder that can cause fruit loss during storage is senescent breakdown. This disorder is most prevalent in apples harvested late and stored for long periods. Symptoms on the skin appear as brown patches while the interior of the fruit develop brown flesh and internal breakdown (Figure 3). Strategies that delay the occurrence of senescent breakdown include harvesting fruits at the right maturity stage, and using an optimum temperature in cold storage.
Physiological disorders of apples resulting from natural aging process could be confused with infection caused by disease pathogens. For accurate diagnosis submit sample to the MU Plant Diagnostic Clinic. For further information on sample collection, packaging and shipping, visit the MU Plant Diagnostic Clinic website: http://plantclinic.missouri.edu/
REVISED: February 21, 2017