Choke disease

The fungus grows within the vegetative tissues of the grass without immediately causing visible harm. Its life cycle involves systematic colonization of the host's stems and leaves throughout the growing season.

A distinctive feature of this pathogen is the formation of a stroma, a dense fungal structure that wraps around the stem. This structure is essential for the production of asexual conidia and sexual ascospores.

The fungus often exhibits a sophisticated co-evolutionary interaction with host plants, where it can be transmitted vertically through seeds or horizontally via spores mediated by insects.

Taxonomically, Epichloe elymi is part of a complex group of fungi that are closely associated with cool-season grasses. Its biology is specifically adapted to the host species within the Elymus genus and related taxa.

The primary symptom of Choke disease is the development of a white, felt-like fungal stroma that encircles the stems of the grass. This stroma hardens over time, giving the stem a choked appearance.

As the stroma grows, it physically prevents the emergence of the inflorescence. The developing seed head is trapped inside the leaf sheath, which is why the disease is commonly called «choke».

Affected plants are often stunted and show visible signs of structural deformation. The infected tillers fail to produce flowers or seeds, significantly impacting the plant's reproductive output.

Visual identification is most successful during the heading phase of the grass. Infected stems are easily distinguished by the pale, thickened, and rigid fungal cover compared to healthy, flexible seed heads.

In addition to the physical symptoms, the presence of the fungus often alters the growth habit of the plant, leading to a loss of vigor and potential death of the specific tiller affected.

The development of Choke disease is highly dependent on environmental conditions, particularly cool and humid weather during the spring growth phase. These conditions favor the proliferation of fungal mycelium.

High planting density in forage fields or lawns creates a microclimate with high humidity, which significantly increases the risk of successful spore germination and subsequent plant infection.

Insect vectors, such as Botanophila flies, play a crucial role in the dissemination of the fungus. They transport fungal spores between plants, which is essential for the sexual reproduction of the pathogen.

Seed-borne transmission is a significant factor in the spread of the disease over long distances. Planting infected seeds leads to systemic infection of the new crop from the very beginning.

Cultural practices that promote rapid vegetative growth, such as high nitrogen fertilization, may inadvertently create more favorable conditions for the systemic spread of the endophyte within the plant.

The most severe impact of Epichloe elymi is the total loss of seed yield in infected tillers. Because the reproductive organs are choked, the plant becomes sterile and cannot produce viable seeds.

In forage and pasture systems, the disease can lead to the thinning of the stand. Over time, the prevalence of infected plants increases, necessitating the renovation of pastures.

Certain strains of endophytes may produce alkaloids that are toxic to grazing livestock, potentially leading to adverse health effects such as staggers or reduced appetite in animals.

The disease reduces the overall longevity of perennial grass stands. The energy diverted to the fungus reduces the plant's competitive ability against weeds and other more vigorous species.

Economic losses are compounded by the costs of removing diseased stands and re-establishing the forage cover with pathogen-free certified seeds.

The use of certified endophyte-free seeds is the most effective preventative measure. Strict quality control during seed production is essential to prevent the spread of the disease.

Regular mowing of the grass before the fungal stroma begins to produce spores can help lower the infection pressure. This disrupts the pathogen's life cycle and prevents further spread.

Maintaining proper spatial isolation between seed production fields and wild grass populations is recommended to minimize the risk of spore introduction by wind or insect vectors.

Breeding for resistance is the long-term solution for managing Choke disease. Selecting grass varieties that naturally resist systemic colonization is a key focus for agricultural research.

Chemical control options are currently limited due to the internal systemic nature of the pathogen within the stem, making cultural management and genetic selection the primary lines of defense.