First Report of Puccinia emaculata Infection on Switchgrass in Virginia.

Area of Science:

• Plant Pathology
• Agronomy
• Genetics

Background:

• Switchgrass (Panicum virgatum) is a vital bioenergy crop with diverse germplasm.
• Foliar rust diseases can significantly impact crop yield and health.
• Understanding disease resistance in different switchgrass ecotypes is crucial for breeding programs.

Purpose of the Study:

• To identify and characterize a rust pathogen affecting switchgrass in Virginia.
• To evaluate the susceptibility of various switchgrass germplasm to the identified rust.
• To determine if ecotype (lowland vs. upland) influences rust resistance.

Main Methods:

• Field observation and collection of infected switchgrass leaves.
• Microscopic analysis of urediniospores and teliospores for morphological identification.
• Molecular identification using PCR amplification and DNA sequencing of the 18S rDNA gene.
• Disease severity scoring on a 0-9 scale for 168 switchgrass germplasm lines.

Main Results:

• A foliar rust pathogen, identified as Puccinia emaculata, infected over 90% of switchgrass lines.
• Upland switchgrass cultivars exhibited moderate to high susceptibility (scores 7-8).
• Lowland switchgrass cultivars displayed moderate to high resistance (scores 3-4).

Conclusions:

• This study confirms Puccinia emaculata as the causal agent of switchgrass rust in Virginia.
• Significant variation in rust resistance exists between lowland and upland switchgrass ecotypes.
• Lowland ecotypes are more resistant to this rust, providing valuable insights for breeding resistant switchgrass varieties.