Sorghum ergot

The causal agent of sorghum ergot is the fungus Claviceps sorghi, which belongs to the Ascomycota division. This specialized pathogen targets the reproductive tissues of the plant. The disease is primarily recognized by the transformation of ovaries into sclerotia, which are hard, dark, fungal structures that replace healthy seeds within the sorghum panicle.

The host range of Claviceps sorghi is focused mainly on cultivated sorghum species, including grain and forage sorghum, as well as some wild sorghum relatives. Infection is strictly limited to the flowering stage of the plant, specifically targeting unfertilized stigmas. Once the fungus invades the floral tissue, it prevents the development of the kernel.

Early symptoms are characterized by the production of honeydew, a sticky, sugary exudate that oozes from the infected florets. This liquid contains conidia of the fungus. As the disease progresses, the honeydew dries up, and distinct, elongated sclerotia emerge from the glumes, often appearing as dark, protruding masses that replace the grain.

Environmental conditions play a critical role in the development and spread of sorghum ergot. The disease thrives in regions experiencing moderate temperatures and high humidity during the flowering phase. Rain and dew are essential for the dispersal of spores, which are transmitted by wind, splashing water, or visiting insects from infected panicles to healthy ones.

The economic impact of this pathogen is significant due to both yield loss and quality degradation. Infected panicles produce fewer kernels, directly reducing the harvest volume. Furthermore, the presence of sclerotia in the grain poses a health risk, as these structures contain toxic alkaloids that make the grain unsuitable for human or animal consumption, leading to potential market rejection.

Effective management strategies focus on preventing the buildup of inoculum and protecting the flowering phase. These include practicing crop rotation to prevent overwintering pathogens in the field, using high-quality clean seeds, and implementing timely weed control to remove wild sorghum hosts. Additionally, planting resistant cultivars and optimizing sowing dates to ensure flowering occurs during drier periods are vital for minimizing the risk of a severe outbreak.