The Complex Viral Etiology of St. Augustine Decline

Area of Science:

• Plant Pathology
• Virology
• Turfgrass Science

Background:

• St. Augustine decline (SAD) is a significant viral disease affecting St. Augustinegrass, a popular turfgrass in the U.S. Gulf Coast.
• Previous research has identified panicum mosaic virus (PMV) as a causal agent, but the role of its satellites has been less clear in field conditions.

Purpose of the Study:

• To identify the viral agents responsible for St. Augustine decline in field-collected samples.
• To investigate the incidence of panicum mosaic virus (PMV) and its associated satellite panicum mosaic virus (SPMV) and satellite RNAs (satRNAs).
• To assess the influence of environmental conditions on disease symptom expression.

Main Methods:

• Field surveys were conducted in two locations in southeast Texas, collecting 204 St. Augustinegrass samples.
• Viral analysis involved detecting the presence of PMV, SPMV, and satRNAs in infected plants.
• Greenhouse studies were performed to observe symptom development and homogeneity over time.

Main Results:

• Analyses confirmed that St. Augustine decline is caused by infection with PMV, either alone or in combination with SPMV and/or satRNAs.
• This study reports for the first time the incidence of PMV satRNAs in field samples of St. Augustinegrass.
• Initial leaf symptoms varied (bleaching to mottle), but greenhouse observations showed a homogeneous chlorotic mottle after 5 months.

Conclusions:

• Panicum mosaic virus (PMV), along with its satellites (SPMV and satRNAs), is confirmed as the causative agent of St. Augustine decline in field conditions.
• The presence of PMV satRNAs in field samples is a novel finding, expanding our understanding of SAD's virology.
• Environmental factors play a crucial role in modulating the phenotypic expression of St. Augustine decline symptoms.