The majority of the work concerning strawberry viruses in North America has been done in the Pacific Northwest and California.
Currently more than thirty viruses and phytoplasmas have been reported in Fragaria (Spiegel and Martin, 1998), The first report of a virus disease in an eastern strawberry field was made in 1931 (Demaree and Marcus, 1951). A search for virus-free eastern strawberry cultivars that was initiated in 1946 represents the first virus survey in eastern North America (Demaree and Marcus, 1951). The authors reported that the majority of plants selected from healthy looking fields in 16 eastern states were determined to be infected when graft indexed on ‘Marshall’ and the East Malling Fragaria vesca L. index plants.
Of particular interest to the eastern North American strawberry industry is the strawberry pallidosis disease that is suspected to be incited by a vector-borne virus currently referred to as pallidosis agent (Fulton, 1987). The disease was originally detected in the United States and Australia in 1957 (Frazier and Stubbs, 1969); however, it appears to be indigenous to North America.
Although the disease has been reported in the western U.S. (Frazier and Stubbs, 1969; Mullin et al., 1975), it is rarely seen in commercial fields and is not considered a primary virus problem there (R. Martin, personal observation). In contrast, graft indexing assays of ‘run-down’ strawberry cultivars and selections from USDA Beltsville fields, routinely produce symptoms on F. virginiana UC-10 but not on F. vesca UC-4 and UC-5 indicators, suggesting strawberry pallidosis disease is present in field plantings and constitutes a potentially significant strawberry disease (S. Hokanson, personal observation). Double-stranded RNA has been identified in plants infected with pallidosis (Yoshikawa and Converse, 1990), but this is not a suitable alternative to graft transmission for virus detection.
The work describe here is an attempt to determine 1) what viruses infect strawberry plants growing in commercial strawberry production fields in the state of Maryland, and 2) at what frequency the viruses occur.