Details on the situation of Iris yellow spot tospovirus in USA and more particularly in Colorado
Iris yellow spot tospovirus (IYSV – EPPO Alert List) is an emerging disease of onions which is spreading in the western United States. So far, IYSV has been found in the following states: Arizona*, California*, Colorado, Idaho, Nevada*, New Mexico*, Utah*, Washington. Reasons for its sudden dissemination and development on onion crops remain unknown. Annual surveys were conducted in Colorado from 2001 to 2003 and showed that the distribution of IYSV has increased dramatically since 2001, although the virus is still absent in southern and north-eastern Colorado. IYSV was confirmed in 1 of 18 fields (5.6%) in 2001, 4 of 24 fields (16.7%) in 2002, and 41 of 56 fields (73.2%) in 2003. In 2003, IYSV was also detected on volunteer onions in several fields where it had been found the previous year. Further studies showed that the presence of IYSV is associated with a general reduction in bulb size.
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* The EPPO Secretariat had previously no data on the occurrence of IYSV in these states.
Sources
Gent, D.H.; Schwartz, H.F.; Khosla, R. (2004) Distribution and incidence of Iris yellow spot virus in Colorado and its relation to onion plant population and yield.
Plant Disease, 88(5), 446-452.