Phoma leaf spot of sorghum

The disease is caused by the fungus Phoma andropogonivora, which belongs to the group of mitosporic fungi. This pathogen is a specific agent that targets the foliage and stems of host plants, causing necrotic damage to the plant tissues through enzymatic activity and colonization.

The primary host of this pathogen is sorghum (Sorghum bicolor). It affects various types of sorghum crops, including grain sorghum, forage, and broomcorn. Wild grasses related to the sorghum genus may also serve as collateral hosts, maintaining the inoculum in the agroecosystem throughout the year.

Symptoms of the disease are characterized by the appearance of spots on the leaves. These lesions often start as small, irregular, or circular brown to dark-reddish spots. As the infection progresses, these spots expand, often merging to cover large areas of the leaf, and develop a distinct center where fungal pycnidia appear as tiny, dark, embedded dots.

The development of Phoma andropogonivora is strongly favored by high humidity, rainfall, and moderate temperatures. Moisture is essential for the germination of conidia and the infection process. The disease spreads rapidly during rainy seasons when water droplets splash spores from infected debris or leaves to healthy plant tissue.

The economic impact of this disease is linked to the reduction of the photosynthetic leaf area. Severe infestations lead to premature leaf senescence, impaired grain filling, and lower overall biomass production. In susceptible hybrids, the disease can cause significant yield losses if left untreated during critical growth stages.

• Use of certified disease-free seeds and appropriate seed treatments.
• Implementation of crop rotation to break the life cycle of the pathogen.
• Deep plowing of crop residues to reduce the primary inoculum load in the field.
• Planting resistant or tolerant sorghum hybrids.
• Application of foliar fungicides when early symptoms are observed, especially under favorable weather conditions.