Phoma leaf spot

Visual signs of dry rot vary by crop, but a common feature is the gradual wilting and browning of tissues. Stems often develop sunken lesions that may eventually be covered with small, reproductive fungal structures or spore-bearing layers.

When affecting root crops or tubers, dry rot manifests as deep, dry ulcers or surface wrinkling. The internal tissue loses moisture, becomes brittle or pithy, and changes color, typically ranging from light brown to charcoal black.

A primary symptom is the destruction of vascular bundles, which disrupts the transport of water and nutrients. This results in the premature yellowing and drying of the above-ground parts of the plant, even when soil moisture is adequate.

On fruits, the disease may appear as a localized spot that expands rapidly, eventually leading to the mummification of the fruit. Unlike soft rots, there is typically no unpleasant odor or liquefaction, which is a key diagnostic characteristic for field identification.

Disease progression is often accompanied by the appearance of spores on the surface of the infected area. The color of this fungal growth can vary from white and pink to dark grey, depending on the specific pathogen and the surrounding environmental conditions.

Dry rot is a collective term for a group of fungal plant diseases characterized by the gradual decay and desiccation of plant tissues without the presence of soft exudates. The primary pathogens in this group are typically imperfect fungi belonging to the genera Fusarium, Phoma, Diplodia, and Macrophomina.

These pathogens act as facultative parasites, capable of surviving in the soil or on plant debris for extended periods in the form of mycelia, sclerotia, or chlamydospores. Depending on the specific fungal species, the disease may target root systems, stems, fruits, or tubers of various agricultural crops.

The biological hallmark of this group is the production of specific toxins that degrade plant cell walls and suppress the host's immune response. Infections often become systemic, spreading throughout the vascular system or entering through mechanical injuries in the plant tissues.

This group includes pathogens that prefer moderately humid conditions and activate during periods of plant stress. They affect a wide range of crops, including cereals, oilseeds, vegetables, and fruit plants, in both open-field and greenhouse environments.

Diagnosis requires mycological analysis, as visual symptoms of dry rot caused by different fungi can appear very similar. Understanding the biology of the specific pathogen is critical for selecting the most effective management strategy.

Dry rot development is favored by a combination of high humidity and moderate temperatures. The optimal range for the activation of spores for many species is +18...+25°C, provided that free moisture is present on the plant surfaces.

Mechanical injury is a key factor for infection, as these wounds provide easy access for fungal spores to colonize the interior tissue. Damage can result from insect activity, hail, poor handling during cultivation, or tissue cracking caused by irregular irrigation.

The ripening stage is a critical period for infection when the plant's natural defenses begin to decline. High planting density and poor ventilation in greenhouses create a microclimate that facilitates rapid disease spread between adjacent plants.

Soil-borne infection occurs when crop rotation is neglected, allowing inoculum to accumulate in the upper soil layers. Pathogens can remain viable in the soil for several years, waiting for favorable conditions to attack the root systems of subsequent crops.

Environmental stressors, such as nutrient deficiencies, extreme temperature fluctuations, or excessive nitrogen fertilization, reduce plant resistance. Under these conditions, even weakly virulent pathogens can cause widespread infection throughout the crop.

The damage caused by dry rot manifests as a significant reduction in yields due to plant death or loss of fruit biomass. Widespread infection often leads to the rejection of a significant portion of the harvest during collection and sorting stages.

Infected products lose their marketability and storage potential. Even if symptoms are invisible at harvest, the fungi can continue to progress in storage facilities, leading to catastrophic post-harvest losses and economic waste.

The disease disrupts metabolic processes, negatively impacting seed quality. Seeds harvested from infected plants often exhibit low germination energy and serve as a primary source of inoculum for the following growing season.

Fungal toxins can accumulate in infected tissues, rendering the crop unsafe for animal feed. This poses a secondary risk to livestock production and significantly increases the overall cost of production for the agricultural enterprise.

Economic losses are compounded by the high costs of fungicide applications and mandatory quarantine measures. In severe cases, dry rot can make the cultivation of certain crops entirely unprofitable for a specific piece of land.

The primary control method is strict adherence to crop rotation, ensuring that susceptible crops are not returned to the same field for at least 3–4 years. This practice effectively disrupts the lifecycle of soil-borne pathogens.

Using certified, disease-free planting material is a mandatory preventive measure. Seed treatment with systemic fungicides is also critical to protect young seedlings from early-season soil infections.

Agronomic practices aimed at strengthening plant immunity include optimized irrigation, balanced mineral nutrition, and timely pest management. Robust, healthy plants are significantly more resistant to fungal pathogen penetration.

After harvest, it is essential to clear fields of all crop debris, which serves as a major reservoir for the fungi. Deep plowing helps accelerate the decomposition of these residues and reduces the population of overwintering pathogens.

During epiphytotic events, chemical control using fungicides from the triazole or strobilurin groups is necessary. Applications should be performed preventively or upon the first signs of disease, following the specific label guidelines for each crop.