Sorghum downy mildew

Peronosclerospora sorghi is a destructive oomycete pathogen belonging to the class Oomycetes. It is the causal agent of sorghum downy mildew, a systemic disease that severely affects sorghum and maize production globally by colonizing the vascular tissues of the host plant.

The infection manifests through distinct chlorotic stripes on leaves, stunting of the plant, and malformation of inflorescences. Severely infected plants often become barren, failing to produce viable seeds or panicles, which leads to significant economic losses in affected fields.

The biological cycle involves both sexual and asexual stages. Oospores, formed within leaf tissues, persist in the soil for several years and act as the primary inoculum. Sporangia, produced under high humidity conditions, are wind-dispersed and facilitate rapid secondary spread throughout the growing season.

Optimal conditions for pathogen development and disease progress include high relative humidity (above 90%) and mild temperatures. Nighttime dew and soil moisture during seedling emergence are critical factors that promote systemic infection, as the pathogen enters the plant through roots or stomata.

Integrated management is essential to mitigate damage. Growers should prioritize the use of resistant hybrids and treat seeds with systemic fungicides, specifically those containing metalaxyl or mefenoxam. Furthermore, maintaining a clean field by removing volunteer sorghum and crop debris helps reduce the soil-borne inoculum pressure.