IRIS YELLOW SPOT VIRUS IN SPAIN: INCIDENCE, EPIDEMIOLOGY AND YIELD EFFECT ON ONION CROPS

Iris yellow spot virus (IYSV) is an emerging pathogen of onion and other Allium crops worldwide. This study focused on the incidence, epidemiology and yield effects of IYSV in bulb onion crops in Spain. Surveys were conducted from 2005 to 2009. Samplings were performed in 101 onion fields with 2,677 onion plants tested in total. Onion transplants, winter onion crops and potential alternative hosts were also sampled. IYSV infection showed a temporal pattern of spread, and the proportion of sites with IYSV-infected plants began to increase rapidly after August. Two early infected fields were detected, and were the only ones with severe economic losses (50-60% crop reduction) due to IYSV. In both cases, onions were grown from IYSV- infected transplants imported from another region. There was no evidence that weeds and volunteer onion can act as alternative host. The use of virus (and vector)-free transplants must play an important role in IYSV management strategies by delaying early-season infection of onion in Spain.