Pathogenicity of Pythium Populations from Corn-Soybean Rotation Fields

Area of Science:

• Agricultural Science
• Plant Pathology
• Soil Microbiology

Background:

• Corn and soybean rotation is a common practice in the U.S. North Central region.
• The impact of long-term rotation on soilborne fungal pathogens affecting both crops remains unclear.

Purpose of the Study:

• To investigate the aggressiveness of Pythium populations from long-term corn-soybean rotation fields on both corn and soybean seedlings.
• To determine the prevalence of highly aggressive Pythium isolates in these agricultural systems.

Main Methods:

• Soil and diseased seedling samples were collected from 73 commercial corn-soybean fields in Iowa (1993-1995).
• 163 Pythium isolates were obtained, pooled into six populations based on sample source, and evaluated for pathogenicity and aggressiveness on corn and soybean.
• Pathogenicity testing included measuring the disease index for each isolate on both crops.

Main Results:

• A high proportion of Pythium isolates from soil (71%), diseased soybean (85%), and diseased corn (87%) seedlings were pathogenic to at least one crop.
• Significant percentages of isolates from all sources (29% from soil, 49-64% from soybean, 43% from corn) were highly aggressive on both corn and soybean.
• Aggressiveness on corn and soybean was highly correlated across Pythium populations and for specific P. ultimum isolates (r = 0.75).

Conclusions:

• Long-term corn-soybean rotation fields harbor diverse Pythium populations with high aggressiveness on both crops.
• These findings highlight a potential risk to crop establishment and yield in rotation systems due to aggressive soilborne fungi.
• Management strategies may need to address Pythium populations capable of infecting both corn and soybean seedlings in rotation.