The pomegranate is a fruit tree increasingly cultivated, both for the fresh market and for juice production, with the global production steadily rising. This trend is also observed in our country, where new plantations have multiplied in recent years. Unfortunately, increased cultivation also brings new issues, especially concerning fungal diseases. One problem causing significant concern among growers, both professional and amateur, is pomegranate black heart. Have you ever opened a seemingly healthy pomegranate only to find it rotten inside? That’s the issue with black heart, also known as heart rot of pomegranate.
In this article, let’s delve deeper into this cryptogamic disease.
What is Pomegranate Alternaria?
Alternaria spp is a large genus of ascomycete fungi, belonging to the class Dothideomycetes, comprising over 300 species. The most common form is Alternata alternata, and it is suspected to be the pathogen responsible for pomegranate black heart. This fungus is highly resilient and can survive saprophytically (as mycelium) for many years in the soil, on decomposing plant residues, or on infected and mummified fruits left unharvested.
What are the symptoms of pomegranate heart rot?
The alternaria pathogen enters the fruit from the calyx area, causing the gradual decay of the arils, hence the name black heart. When you open an affected fruit, the rot can be brown (the so-called soft form) or black (dry form). The significant issue with this pomegranate disease is that the fruits generally appear perfectly healthy externally. It does not typically affect the entire plant’s production, but a variable percentage ranging from 5 to 50% (peaks observed in Greece and Israel). This poses the risk that the fruit, inedible and unusable for juice, ends up in the unsuspecting consumer’s shopping cart, who, upon opening it, encounters a bitter surprise. This challenging-to-control factor somewhat compromises the pomegranate’s “reputation”, potentially leading to an overall market demand decrease.
External Symptoms of Pomegranate Black Heart
We mentioned that it’s difficult to detect the symptoms of alternaria attack on the fruit. At most, you might observe a darker skin color with black speckles, signs insufficient for certain disease recognition, especially to an inexperienced eye and in the hurried phases of harvesting. It’s easier to understand an alternaria attack by observing the tree’s leaves, which can show pinpoint black spots, yellowing, and premature shedding. Of course, not all vegetation is affected, making this factor not entirely conclusive for early disease recognition, at least in intensive pomegranate cultivation.
Peak Risk Period for pomegranate heart rot
According to various field tests, this pathogen generates the disease under specific conditions. Generally, pomegranate alternaria strikes in late spring, between flowering and the setting of the tiny fruits. Essentially, the fungus penetrates the newly formed fruit and develops alongside it, causing the rotten black heart.
Pollinating insects can also be vectors. The primary entry points are micro-lesions on the fruit’s skin. The predisposing environmental factors are mild climate combined with very rainy periods, conditions not hard to come by in spring.
How to Naturally Prevent Pomegranate Black Heart
To prevent pomegranate black heart, you must first work on the best possible cultural conditions. Firstly, the soil must be well-drained, avoiding water stagnation that favors the alternaria pathogen. Excessive fertilization, causing overly favorable vegetative growth, which also benefits the fungus, should be avoided.
Summer water stress should be avoided, ensuring regular irrigation, thus preventing the classic pomegranate splitting, another possible entry point for the pathogen.
During vegetative rest, you should prune the pomegranate correctly, ventilating the vegetation. The more air circulates between the plants, the lower the chances of creating conditions of relative humidity favorable to the fungus. Finally, if plants and fruits have been affected by alternaria, at the end of the season, remove from the field vegetation residues and potentially infected mummified fruits, which are sources of inoculum for the fungus in the following season.
Preventing Pomegranate Black Heart with Biological Remedies
There are few treatments with products allowed in organic farming to prevent pomegranate black heart. Firstly, you can use classic fungicides based on copper salts. Another usable product is sulfur, especially in liquid formulations.
As microbiological products against pomegranate alternaria, Bacillus subtilis and Bacillus amyloliquefaciens are being tested, bacteria common in the soil but with few field applications that have rigorously tested their efficacy against this specific pathology. In any case, all treatments should be applied immediately after the end of flowering, thus respecting the invaluable action of pollinating insects, crucial for satisfactory pomegranate yields.