Colletotrichum riograndense

Pathogen and disease type. Colletotrichum riograndense is a pathogenic fungus belonging to the genus Colletotrichum, known to cause anthracnose in various plants. This organism is a hemibiotroph that infects plant tissues by penetrating the epidermis, eventually causing necrotic lesions. It persists in infected plant debris, soil, and seeds, serving as a primary source of inoculum for subsequent growing seasons.

Host range and economic impact. The pathogen is primarily associated with leguminous crops, particularly soybeans. The impact of the disease is significant, resulting in yield losses due to pod blight, seed discoloration, and reduced seed viability. In cases of severe infestation, the disease can cause systemic collapse of the plant vascular system, leading to stunted growth and reduced crop market value.

Symptoms and signs of infection. Symptoms typically appear as irregular, dark, sunken lesions on stems, petioles, and pods. Within these lesions, the fungus develops acervuli, which appear as tiny black dots. Under conditions of high humidity, these structures produce a visible mass of conidia, often appearing as a pinkish or cream-colored mucilaginous substance on the surface of the affected plant tissue.

Conditions for development. The spread of Colletotrichum riograndense is highly dependent on environmental factors. The fungus thrives in warm temperatures ranging from 20°C to 28°C and high relative humidity levels. Splashing rain and wind act as the primary mechanisms for the dispersal of spores from debris to healthy plant parts, making wet growing seasons particularly conducive to outbreaks.

Management and prevention. Controlling Colletotrichum riograndense requires an integrated approach to reduce the inoculum load. Recommended practices include:

• Using high-quality, fungicide-treated seeds.
• Implementing crop rotation cycles involving non-host species for at least three years.
• Managing crop residues through deep tillage or destruction to break the infection cycle.
• Monitoring fields for early symptoms during flowering and pod development stages.
• Applying foliar fungicides as a preventive measure in regions with a history of anthracnose outbreaks.