Watercore

Water core is a disorder of apples where the typical symptom is liquid-soaked tissue around the vascular bundles. This disorder is more common near the core and around the primary vascular bundles, but it may occur in any part of the flesh tissue.

In severe cases, most of the flesh tissue and core area become hard and glassy and the symptoms may be externally visible. The glassy appearance results from liquid in the intercellular spaces. The name is imprecise because affected tissue is not always restricted to the core area.

The liquid has a soluble solids content comparable to that of juice from normal tissue. The main sugars in normal tissue are sucrose, glucose and fructose, but the liquid in water core tissue contains mainly sorbitol, a translocated sugar. If you eat fruit showing water core symptoms the flesh will taste very sweet. Sorbitol is not used directly by apple tissue; it must first be converted to fructose. Water core tissue lacks the ability to convert sorbitol to fructose. High levels of sorbitol lead to the accumulation to ethanol and acetaldehyde, which cause browning and breakdown of the cells of the fruit in storage.

Fruit with slight water core recover during several months in cold storage, without apparent injury. Severely affected fruit, however, develop internal browning and breakdown during storage.

Harvesting at early to optimum maturity can minimise water core in apples. Raising the calcium content in fruit and reducing the use of nitrogen fertiliser decrease the incidence of the disorder. Water core has become quite evident in this year's crop. Growers need to be aware of the symptoms.