When I was in Turkey, pomegranate bushes were almost as common as orange trees in Florida and there was nothing more refreshing than delving into a freshly picked fruit. On occasion, however, there may be black seeds in the pomegranate fruit. What is the cause of pomegranates with black seeds, or rot inside?
What is Black Heart Disease?
The pomegranate (Punica granatum) is a deciduous, bushy shrub which will grow to between 10-12 feet (3-4 m.) tall and bears brightly colored fruit with a plethora of seeds inside of it. The bush can be trained or pruned into more of a tree shape as well. The limbs are thorny and punctuated with dark green, glossy leaves. Spring brings forth the brilliant orange-red blooms, which are either bell-shaped (female) or vase like (hermaphrodite) in appearance.
The edible part of the fruit (aril) is composed of hundreds of seeds that are surrounded by juicy pulp containing a seed coat. There are several varieties of pomegranate and the aril juice can range in color from light pink to dark red, yellow, or even clear. Flavor of the juice varies as well from acidic to quite sweet. Usually the rind is leathery and red but can also be yellow or orange in hue. A rotting or blackened center in this fruit is referred to as black heart of pomegranate. So what is this black heart disease?
Help, My Pomegranate Has Heart Rot
The increasing popularity of pomegranates has directly increased commercial production. The incidence and economic blow of black heart disease has lead major growers to attempt to locate the source of the rot or black seeds in their pomegranates. When a pomegranate has heart rot, it is no longer saleable and the producer risks losing crop income.
Black heart disease has no external symptoms; the fruit looks perfectly normal until one cuts it open. A significant number of tests have been performed to locate the cause of black heart in the hopes of finding some method of control. Finally, the fungus Alternaria was isolated as the major source of black heart disease. This fungus enters the blossom and then on into the resulting fruit. Some studies suggest that the blooms infected with the fungus give off its spores. These spores may then enter damaged fruit, those that have been punctured by the thorny branches or are otherwise cracked. Also, research seems to suggest that the disease afflicts more fruit when there is an abundance of rain during the blooming season.
The infection process is not completely understood, and the type of Alternaria resulting in the infection is still being isolated. Long and short, there is no control for black heart disease. Removal of old fruit from the tree during pruning may aid in eliminating the potential source of the fungus.