Soybean Cercospora leaf blight

Cercospora kikuchii is a significant phytopathogenic fungus classified within the kingdom Fungi and the class Dothideomycetes. It is the specific causal agent of Cercospora leaf blight and purple seed stain in soybeans (Glycine max), a disease complex that poses a global threat to soybean production quality.

The pathogen attacks all aerial parts of the plant, including leaves, stems, pods, and seeds. A diagnostic symptom is the development of reddish-purple to dark brown lesions on foliage, while on the seeds, the fungus produces a distinct purple discoloration of the seed coat, which is often termed "purple seed stain."

The life cycle of the pathogen begins with the survival of mycelia in crop debris and infected seeds. During the growing season, high humidity and warm temperatures (ranging from 25°C to 30°C) trigger the production and dispersal of conidia via wind and water splashing. These spores infect the host tissue, leading to secondary cycles of infection throughout the reproductive stages of the soybean plant.

Economic damage stems from reduced photosynthetic capacity, leading to premature defoliation and pod drop. Furthermore, the accumulation of the toxin cercosporin within the seeds leads to severe downgrading of grain quality, reduced germination rates, and potential rejection by processors due to contamination.

Effective disease management strategies include:

• Selection of high-quality, fungicide-treated seeds to ensure pathogen-free starts.
• Implementation of crop rotation sequences that break the life cycle of the fungus.
• Deep tillage practices to bury infected crop residues and limit inoculum sources.
• Timely application of foliar fungicides, such as strobilurins and triazoles, during the R3–R5 growth stages to protect developing pods and leaves.