Survey of strawberry viruses occurring in commercial plantings in the State of Maryland, USA.
Strawberry plant and leaf samples were collected from 23 commercial farms in 10 counties of Maryland, USA, during June-August 1998, and were subjected to grafting assays and ELISA for the occurrence of different plant viruses. Of the 128 whole plants that were graft assayed, 71% were positive on Fragaria virginiana UC-10, indicator for strawberry pallidosis, while 30% were positive on F. vesca UC-4 or UC-5, indicators for strawberry crinkle virus (SCV), strawberry mild yellow edge virus (SMYEV), strawberry mottle virus (SMV), strawberry vein banding virus (SVBV) and tomato ringspot virus (ToRSV), after 5 weeks following grafting. With regard to plant age, all six-year-old plants were positive on UC-10, while 67% tested positive on UC-4 or UC-5. Neither of the 2 four-year-old plants were positive on either indicator. Of the 20 three-year-old plants tested, 100 and 75% were positive on UC-10, and UC-4 or UC-5, respectively. Of the 52 two-year-old plants tested, 67 and 27% were positive on UC-10, and UC-4 or UC-5, respectively. Of the 44 one-year-old plants tested, 61% were positive on UC-10, while only 11% were positive on UC-4 or UC-5. In case of new plantings, 71% were positive on UC-10, while none was positive on UC-4 or UC-5. Of the 1124 samples tested using ELISA, 7% were positive for SMYEV, 2% were positive for tobacco streak virus and 0.2% were positive for tomato ringspot virus. Results from the leaf grafting assays on UC-10 performed at Beltsville suggest that strawberry pallidosis is the major virus or virus-like problem affecting the Maryland strawberry industry. Pallidosis appears to be fairly evenly distributed among the age classes of plantings, suggesting the disease is transmitted quickly to new plantings.