Further evidence that shallot yellow stripe virus (SYSV) is a distinct potyvirus and reidentification of Welsh onion yellow stripe virus as a SYSV strain

An antiserum to shallot yellow stripe virus (SYSV) was raised and used in c ombination with a range of other antisera to potyviruses of Allium spp. in electron microscopic decoration experiments. The serological results corrob orated an earlier finding that the type isolates of SYSV and Welsh onion ye llow stripe virus (WoYSV) are closely related to each other and only distan tly related to onion yellow dwarf (OYDV) and leek yellow stripe (LYSV) viru ses, the two other major potyviruses infecting Allium spp. Moreover, the de coration results indicated that Japanese potyviruses named OYDV and Wakegi yellow dwarf virus are isolates of SYSV. Sequence analysis of the 3'-termin al regions of the SYSV and WoYSV genomes revealed coat protein (CP) amino a cid and 3'-nontranslated region (3'-NTR) nucleotide sequence identities of 95 and 89%, respectively. The CP amino acid and 3'-NTR nucleotide sequences of these viruses differed from those of OYDV and LYSV by >25 and >67%, res pectively. The serological and molecular studies showed that SYSV and WoYSV are different strains of a potyvirus distinct from OYDV and LYSV. For prio rity reasons, we propose that these strains together with the Wakegi-type i solates of OYDV described in Japan be referred to as SYSV and that SYSV iso lates from Allium spp, other than shallot be designated as the Welsh onion strain of SYSV (SYSV-Wo).