Gordon Johnson, Extension Vegetable & Fruit Specialist; email@example.com
We are seeing increased incidence of water ring and water belly in watermelon fruit this year. Water ring and water belly is associated with water management, environment, and foliage health. It is found most commonly on fields after heavy rains or if irrigation is heavy, humidity is high and skies are overcast, and foliage is diseased.
This disorder is caused by the accumulation of water in the fruit coinciding with slowed solute (sugar) accumulation. Excess water accumulates at the bottom of the fruit or just beneath the rind in a ring, leaving a water-soaked appearance in the flesh when cut open. Water accumulates during cloudy weather when transpiration from fruits is low. It is often worse in fields where foliage has deteriorated and sugar accumulation is reduced. In this situation, water is still being translocated in the xylem but there is limited transpiration through the leaves. Watermelon fruits are still transpiring, but due to the nature of the fruit (thick rind, waxy surface); transpiration is lower than in leaf tissue, leading to water buildup in the fruit. At the same time solute accumulation has been reduced because foliage is compromised leading to cells full of water but with little sugar.
Water ring in watermelon (anonymous source)