CHARACTERIZATION OF IRIS YELLOW SPOT VIRUS ISOLATES FROM ONION CROPS IN NORTHERN ITALY
L. Tomassoli, A. Tiberini, V. Masenga, V. Vicchi, M. Turina
During spring and summer of 2007 and 2008, a number of onion fields in Emilia Romagna region (northern Italy) showed various virus-like symptoms. DAS-ELISA carried out in 2007 and early 2008 for Impatiens necrotic spot virus (INSV), Iris yellow spot virus (IYSV) and Tomato spotted wilt virus (TSWV) showed the occasional presence of TSWV, whereas a number of samples also reacted weakly with IYSV antiserum. In a number of TSWV-negative samples, electron microscopy of leaf extracts revealed the presence of tospovirus-like particles. Western blot analysis on the same set of samples gave positive results with antisera against Tomato fruit yellow ring virus (TFYRV) and IYSV, two serologically related virus species. Sequence analysis of RT-PCR fragments confirmed that the virus in the onion samples was IYSV with approximately 98% identity at the amino acid level with reported Serbian and Spanish sequences of the same virus. Phylogenetic analysis confirmed that the Italian IYSV isolates belong to a newly defined southern European clade. Our data suggest that IYSV is made up of a heterogeneous and serologically distinct group of isolates.