Gnomoniopsis rot

The primary symptom of the infection is brown rot of the nuts, which is often detected only after harvest or when the chestnut is cracked open.

Dark, sunken spots may appear on the surface of young nuts, eventually expanding to cover the entire fruit.

On branches and shoots, the disease manifests as necrosis and cankers, which cause the death (dieback) of the distal parts of the branches.

Under high humidity conditions, a whitish-pink mold, representing the conidial spore mass of the fungus, can be observed on affected bark or nuts.

Leaves on infected branches may yellow and fall prematurely, and in cases of severe infection, mass death of young shoots occurs.

The causal agent of the disease is the ascomycete fungus Gnomoniopsis smithogilvyi. This pathogen specializes in infecting the sweet chestnut (Castanea sativa) and other species within the Castanea genus.

The fungus is an endophyte, which allows it to reside within plant tissues for extended periods without showing visible symptoms until environmental conditions become favorable for active reproduction.

The pathogen can survive in fallen leaves, fruit remnants, and infected branches, which serve as the primary sources of spore dissemination during the growing season.

The infection cycle includes both sexual spore production (ascospores) and asexual reproduction (conidia), ensuring high adaptability of the fungus in colonizing new plant parts.

The fungus penetrates tissues through wounds, natural openings, or directly through the epidermis of the nuts, particularly where pests have caused prior damage.

The development of the fungus is favored by long periods of high humidity and moderately warm temperatures throughout the growing season.

Spore dissemination occurs primarily during rainfall, as water droplets transport conidia to healthy parts of the tree canopy.

The presence of insect pests in the orchard, such as the chestnut gall wasp, significantly increases the risk of infection by providing entry points for the fungus.

Dense plantings with poor air circulation create localized zones of high humidity, which promote active sporulation and spread.

Tree stress caused by drought or mechanical damage during pruning makes trees more susceptible to fungal colonization.

The main economic threat is the significant loss of marketable fruit quality, as infected nuts become unsuitable for storage and consumption.

The disease causes premature fruit drop, leading to direct yield reduction and financial losses for growers.

Systemic infection of the canopy weakens trees, reducing their annual growth and potential for fruit production in subsequent years.

In neglected cases, progressive dieback of scaffold branches may occur, potentially leading to the death of the tree if pathogen pressure is high.

The spread of the infection in nurseries jeopardizes the availability of healthy planting material, hindering the development of the chestnut industry.

A key preventive measure is orchard sanitation: the collection and destruction of fallen nuts, leaves, and infected branches.

Regular pruning of the canopy is recommended to improve air circulation and remove necrotic shoots that harbor the infection reservoir.

An essential aspect of protection is pest control, particularly targeting the chestnut gall wasp, to reduce the number of entry points for the fungus.

Application of fungicides during the most susceptible growth stages can reduce infection levels, but chemical methods should be combined with cultural practices.

Using resistant cultivars and maintaining optimal growing conditions are the foundations of a long-term orchard protection strategy.