Sorghum downy mildew

Sorghum downy mildew (Sclerospora sorghi) is a devastating obligate biotrophic pathogen belonging to the class Oomycetes. As an oomycete, it is taxonomically distinct from true fungi and is known for causing systemic infections in major cereal crops, leading to significant physiological disruption within the host tissues.

The primary hosts of this pathogen include grain sorghum, sweet sorghum, maize, and sudangrass. Typical symptoms manifest as chlorotic streaks on the foliage, severe stunting of the plant height, and the transformation of the inflorescence (panicles or tassels) into leafy, sterile structures, which effectively prevents grain formation and yield accumulation.

The life cycle of Sclerospora sorghi involves the production of oospores, which serve as long-term survival structures in the soil. These oospores can remain viable for several years, providing the primary source of inoculum. Upon germination, the pathogen infects the roots or mesocotyls of young seedlings, after which the mycelium grows systemically throughout the developing plant.

Environmental conditions play a critical role in disease epidemiology. The pathogen thrives under conditions of high soil moisture and moderate temperatures, typically between 20°C and 25°C. These conditions promote both oospore germination and the subsequent colonization of the host, making damp, poorly drained soils particularly high-risk areas for disease outbreaks.

Economic damage is severe, as infected plants are often completely sterile and provide zero yield, while secondary infections can reduce plant vigor significantly. Control strategies focus on integrated pest management:

• Utilizing resistant or tolerant crop hybrids.
• Implementing long-term crop rotation schemes.
• Treating seeds with specialized systemic fungicides to protect seedlings.
• Ensuring proper field drainage to minimize favorable conditions for the pathogen.