Watercore
Watercore occurs in most apple-producing areas but is most of a concern in areas with arid or semi-arid climates. It is very common in late harvested apples. Cultivars susceptible to watercore include Delicious, Jonathan, Stayman, Fuji and Honeycrisp.
Identification
Watercore is an abiotic disorder causing water-soaked regions to form in the flesh of the apple. Flesh tissue of the apple appears translucent and the intercellular spaces are filled with a sugar-water solution. Severe cases of watercore cause fruit to appear hard and glassy, and may be externally visible. In mild and moderate cases, symptoms are more commonly found near the core and around the primary vascular bundles, but may occur in any part of the apple.
It was impossible in the past to detect internal symptoms of the disorder without cutting open the fruit. More recently, equipment has been developed to detect and segregate several classes of watercore by measuring light transmittance through the fruit.
Biology
Watercore is more of a problem where heat and sunlight are intense. High temperatures when apples are approaching maturity favour its development. The disorder often occurs on fruit exposed to the sun, and a severe form of the disorder is often associated with sunburn. As apples become over mature, watercore often increases rapidly.
Affected fruit are more likely to exhibit internal breakdown and alcohol off flavours during mid- to long-term storage. However, slight watercore may dissipate during storage.
While the exact cause of watercore is not well understood, it is thought to be linked to changes in membrane integrity associated with maturation and ripening.
Management Notes
- Picking fruit before watercore develops – and at the proper state of maturity – is important to reduce the incidence of watercore.
- Adequate calcium nutrition and careful use of nitrogen fertilizers helps minimize damage in susceptible varieties.
- Susceptible varieties include Jonathan, Delicious, Honeycrisp, Stayman, Winesap, Granny Smith and Fuji.
- Watercore is associated wtih large fruit, high leaf to fruit ratio, high fruit nitrogen and boron, low fruit calcium, excessive thinning, high light exposure and Ethrel sprays.
- Another type of watercore occurs during unusually hot weather. This watercore is found more on the exposed side of the apple and is associated with sunscald.
- Do not place fruit with moderate to severe water core in controlled atmosphere. Market it quickly.
