Cold-Stressed Soybean Sensitivity to Charcoal Rot

Area of Science:

• Plant Pathology
• Agronomy
• Climate Science

Background:

• Charcoal rot, caused by *Macrophomina phaseolina*, is a significant soybean disease, exacerbated by heat and drought.
• The impact of early-season cold spells on soybean susceptibility to charcoal rot is not well understood.
• Climate variability includes unpredictable temperature fluctuations, affecting crop health.

Purpose of the Study:

• To investigate if transient chilling increases charcoal rot severity in soybean.
• To determine if soybean cultivar differences influence predisposition to charcoal rot following cold stress.
• To quantify the interaction between cold stress and charcoal rot development.

Main Methods:

• Nine soybean cultivars (Maturity Groups 00, 0, and 0-I) were subjected to optimal conditions or a three-day cold spell.
• Cold spell initiated at the first fully expanded trifoliate (20-23 days after sowing).
• Standardized cut-stem inoculation with *M. phaseolina* at 26 days after sowing, with lesion length assessed over 21 days post-inoculation.

Main Results:

• Cold stress significantly increased soybean stem lesion lengths across all assessment points.
• The most pronounced differences between treatments were observed at the earliest measurement post-inoculation.
• Significant genotype and treatment × genotype interactions revealed differential cultivar susceptibility to cold-induced predisposition.

Conclusions:

• Brief early-season cold exposure can predispose soybean to increased charcoal rot severity.
• The magnitude of this predisposition is dependent on soybean genotype and the timing of cold stress.
• Integrating cold-stress tolerance into soybean breeding programs can enhance resilience to climate variability.