Sorghum ascochyta blight

Sorghum ascochyta blight is a fungal disease caused by the pathogen Ascochyta sorghi. Systematically, this organism is classified within the kingdom Fungi and the genus Ascochyta. It functions as a facultative parasite, surviving adverse conditions by forming pycnidia — small, flask-shaped reproductive structures that contain conidia, which serve as the primary inoculum for the spread of the disease during the growing season.

The disease specifically impacts plants in the genus Sorghum. The symptoms are primarily observed on the leaves as irregular or oval-shaped spots. These spots initially appear light-colored, often with a darker, distinct margin. As the lesion matures, the central necrotic tissue becomes peppered with minute dark pycnidia, which are diagnostic indicators for identifying this specific pathogen in the field.

The life cycle of the pathogen is driven by the presence of crop residue. During the winter, the fungus remains dormant in the soil or on infected stalks. In the spring, when temperatures rise to 20–25°C and moisture becomes available through rain or heavy dew, the pycnidia exude conidia. These spores are then dispersed by rain splashes or wind currents onto the leaves of emerging sorghum crops, initiating the infection cycle.

The economic impact of ascochyta blight is primarily tied to the reduction of photosynthetic area on the leaves. When infection levels are high, the premature death of leaf tissue reduces the plant's capacity to fill grain, leading to lower yields and lower grain quality. In susceptible cultivars and favorable weather conditions, severe defoliation can significantly reduce overall harvest weight and forage quality.

Effective management requires an integrated pest management (IPM) strategy. Essential practices include rotating sorghum with non-host crops and plowing under crop residues to accelerate decomposition. Using certified, healthy seed is the first line of defense. Furthermore, when environmental conditions favor disease development, the application of foliar fungicides is highly recommended to protect the crop and minimize yield loss.

• Pathogen type: Ascomycete fungus.
• Key diagnostic sign: Dark pycnidia in leaf lesions.
• Optimal conditions: Warm temperatures and high humidity.
• Management priority: Residue destruction and fungicide usage.