Colletotrichum graminicola

Colletotrichum graminicola is a phytopathogenic ascomycotic fungus of global importance, recognized as the causal agent of anthracnose in corn crops (zea mays) and other grasses.

Its ability to cause significant damage in tropical and subtropical regions, combined with the complexity of its life cycle and genetic variability, makes it one of the most studied pathogens in plant pathology.

Taxonomy and classification

Colletotrichum graminicola belongs to the genus Colletotrichum, family Glomerellaceae, order Glomerellales.

Its taxonomy is marked by the existence of two reproductive stages: the anamorph (asexual phase), characterized by the production of conidia, and the teleomorph (sexual phase), called Glomerella graminicola.

Molecular studies using markers such as ITS, GAPDH and TUB2 were fundamental to differentiate it from closely related species, such as C. sublineola, with which it shares secondary hosts.

• Kingdom: Fungi

• Phylum: Ascomycota

• Class: Sordariomycetes

• Order: Glomerellales

• Family: Glomerellaceae

• Genre: Colletotrichum

• Species: Colletotrichum graminicola

Biology and life cycle

The fungus exhibits a biphasic life cycle, alternating between biotrophic and necrotrophic strategies.

In the asexual phase, the hyaline, unicellular, fusiform conidia are disseminated by water, wind or insects, germinating in conditions of high humidity (25–30°C). After adhesion to the leaf surface, appressoria are formed that penetrate the plant through stomata or cuticle, using hydrolytic enzymes (cutinases, pectinases) and mechanical pressure.

In the biotrophic phase, the fungus colonizes living tissues, suppressing plant defenses through effectors.

Subsequently, in the necrotrophic phase, it induces tissue necrosis, releasing toxins (e.g. colutelin) and degrading cell walls for nutrition.

The sexual phase, although less frequent, contributes to genetic diversity via the formation of perithecia and ascospores.

Etiology and symptomatology

Anthracnose caused by C. graminicola manifests itself in corn leaves, stalks and ears.

On the leaves, elongated lesions with dark edges and a necrotic center appear, evolving into "burning" of the tissue.

In the stalk, rot weakens the structure, causing lodging, while in the ears, it leads to grain deterioration.

The disease is favored by hot, rainy climates with prolonged periods of leaf wetness. Varietal susceptibility and abiotic stress exacerbate symptoms.

Differentiation of related species

The distinction between C. graminicola e C. sublineola, a pathogen of sorghum, requires integrated analysis. While C. graminicola predominantly infects corn, C. sublineola specializes in sorghum.

Morphologically, the conidia of C. graminicola are larger (12–20 µm) and their arrows are shorter and thicker. Molecularly, sequences of genes such as GAPDH and TUB2 reveal specific polymorphisms.

Cross-pathogenicity tests confirm host specialization: C. graminicola does not cause severe damage to sorghum, and vice versa.

Integrated management

Anthracnose reduces corn productivity by up to 50% in epidemic outbreaks, affecting grain quality and plant stability for mechanized harvesting.

Management requires a multifaceted approach:

• Genetic resistance: cultivars with Rcg1 and Rcg2 genes show tolerance to infection.

• Cultural practices: crop rotation, elimination of infected residues and rational irrigation management reduce inoculum.

• fungicides: applications of triazoles and benzimidazoles at critical stages (e.g. flowering) control the disease, although resistance is a risk.

• Monitoring: Early diagnosis via PCR and symptom analysis prevents outbreaks.

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