Sources of Iris yellow spot virus in New York

Iris yellow spot virus (IYSV) has been found consistently in commercial dry bulb onion fields throughout New York State since 2006. Yearly recurrence of IYSV may result from annual reintroductions of the virus or persistence of the virus in overwintering host plants. To identify potential sources of IYSV, we surveyed onion transplants imported into New York as well as volunteer onion plants and weeds using a double-antibody sandwich enzyme-linked immunosorbent assay. IYSV was not found in any of 1,097 transplant samples tested in 2007 but 4 of 760 (0.53%) transplant samples tested positive in 2008. IYSV was found in volunteer onion plants in 3 of 10 (30%) onion fields sampled in 2007, in 4 of 27 (15%) onion fields sampled in 2008, and in 6 of 12 (50%) onion cull piles sampled in 2008. In all, 4 of 17 weed species (i.e., chicory [Cichorium intybus], common burdock [Arctium minus], curly dock [Rumex crispus], and dandelion [Taraxacum officinale]), were confirmed to be infected with IYSV using serological and molecular testing methods. IYSV may be reintroduced annually into New York through imported onion transplants but it also persists in volunteer onion plants and selected weed species.