Evidence for a Pythium sp. as a Chronic Yield Reducer in a Continuous Grain Sorghum Field

Area of Science:

• Plant Pathology
• Agronomy
• Agricultural Science

Background:

• Continuous grain sorghum production systems can foster soilborne diseases.
• Pythium species are known pathogens affecting grain sorghum, causing stalk rot and stand reduction.

Purpose of the Study:

• To investigate the impact of Pythium seed and root rot in continuous grain sorghum.
• To evaluate the efficacy of metalaxyl and captan seed treatments in mitigating disease and improving yields.

Main Methods:

• Field experiments conducted over 4 years in a long-term continuous grain sorghum field.
• Evaluation of seed treatments (metalaxyl, captan) on plant stands, vigor, and grain yield.
• Isolation and identification of fungal pathogens (Pythium ultimum var. ultimum) and greenhouse verification using Koch's postulates.

Main Results:

• Metalaxyl seed treatment increased grain yields by an average of 24.0% compared to untreated seed across five experiments.
• Metalaxyl outperformed captan, increasing yields by 13.1% in three out of four trials.
• Yield increases were observed despite no consistent improvements in plant stands or early-season vigor, suggesting chronic sub-clinical root damage.

Conclusions:

• Pythium ultimum var. ultimum causes significant chronic seed and root rot in continuous grain sorghum, negatively impacting yield.
• Metalaxyl provides effective protection against Pythium seed and root rot for at least 28 days post-planting.
• Seed treatment with metalaxyl is a viable strategy to enhance grain sorghum productivity in fields with a history of continuous cropping.