Panicum mosaic virus

Panicum mosaic virus (PMV) is a pathogenic plant virus noted for causing the grass disease St. Augustine Decline. It is a positive-sense ssRNA virus and the type species of the genus Panicovirus, readily spread by humans through tools such as lawn mower blades, but not known to be spread via biological vectors such as insects. PMV was identified in 1953, and is known to infect switchgrass, centipedegrass and St. Augustine Grass.

History

PMV was first observed in Kansas in 1953. It was originally noted to infect switchgrass (Panicum virgatum), and was observed infecting St. Augustine Grass (Stenotaphrum secundatum) in Texas in 1966. The strain specific to St. Augustine Grass has since been observed in Arkansas, Louisiana, Mississippi and South Carolina in the United States, as well as in Mexico. Other strains have been identified infecting centipedegrass (Eremochloa ophiuroides).^[1] Foxtail millet (Setaria italica), white proso millet (Panicum miliaceum) and pearl millet (Pennisetum glaucum) have also been used to propagate PMV and panicum mosaic satellite virus (SPMV), and mechanical transmission can occur to maize and some cultivars of common wheat (Triticum aestivum).^[2]

Classification

Panicum mosaic virus is the type species of the genus Panicovirus, a member of the plant virus family Tombusviridae.^[1] Members of Tombusviridae are transmitted as positive sense single-stranded non-enveloped RNA viruses, with an icosohedral capsid.^[3] PMV itself has a genome of 4,326 nucleotides, encapsulated into 30-nm particles by a capsid protein of 26 kDa.^[1] PMV was placed in the genus Panicovirus because of its limited monocot host range and lack of an additional 5'-ORF. PMV is serologically related to Molina streak virus and Maize mild mottle virus.^[2]

St. Augustine Decline

St. Augustine Decline (SAD) is a viral disease of St. Augustine Grass (Stenotaphrum secundatum), and is the only economically important viral disease in turf management. Research into SAD has implicated PMV, though panicum mosaic satellite virus plays an unknown role in the disease.^[1] In SAD, grass blades develop a mottled, chlorotic appearance, and the disease can eventually spread across large sections of turf.^[4] Early SAD may be confused with iron chlorosis, although the latter is characterized by either a uniform yellowing or characteristic yellow striping that appears parallel to the mid-vein on the leaf.^[5]

There is currently no cure or treatments for SAD, with the most common solution being to replace all diseased areas with a disease resistant cultivar of St. Augustine Grass (such as Floralawn, Floratam, Raleigh and Seville).^[4][5] The newly planted resistant grass will ultimately crowd out the infected areas, although this often requires waiting at least one full year, if not more, as the diseased grasses are gradually overtaken by those planted, resistant patches.

Transmission is believed to happen primarily by mechanical means, such as from lawn mower blades spreading the disease from cutting diseased portions and then infecting other areas of one's lawn. As such, commercial lawn cutting services are especially problematic and have led to SAD becoming more of an issue by serving to spread the disease beyond just a single lawn/area of turf.^[1][5]

References