Monitoring and Tracking Changes in Sensitivity to Azoxystrobin Fungicide in Alternaria solani in Wisconsin

Area of Science:

• Plant Pathology
• Agricultural Entomology
• Molecular Biology

Background:

• Azoxystrobin is a widely used fungicide for managing Alternaria solani in Solanaceous crops.
• Repeated applications of azoxystrobin have raised concerns regarding decreased fungal sensitivity.
• Monitoring is crucial to understand fungicide resistance development in plant pathogens.

Purpose of the Study:

• To investigate the in vitro sensitivity of Alternaria solani to azoxystrobin.
• To identify genetic mutations associated with decreased azoxystrobin sensitivity in A. solani.
• To correlate sensitivity changes with agricultural practices in Wisconsin potato fields.

Main Methods:

• Fungal monitoring and sensitivity testing of Alternaria solani isolates from commercial potato fields.
• Quantitative real-time polymerase chain reaction (qPCR) to detect mutations in the cytochrome b gene.
• Comparison of sensitivity data from 2002-2003 with baseline data from 1998.

Main Results:

• Isolates of A. solani collected in 2002 and 2003 showed a 20-fold increase in mean effective concentration (EC50) for azoxystrobin compared to 1998 baseline isolates.
• Decreased sensitivity was linked to site-specific mutations in the cytochrome b gene, specifically the F129L substitution.
• While the G143A substitution (conferring resistance) was not found, all three mutations leading to F129L were detected, with varying frequencies across sites and years.

Conclusions:

• A significant decrease in azoxystrobin sensitivity has emerged in Wisconsin A. solani populations.
• The F129L mutation in the cytochrome b gene is associated with reduced azoxystrobin sensitivity in this pathogen.
• Fungicide sensitivity changes are influenced by specific disease management practices, highlighting the need for strategic application.