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First Report of Iris yellow spot virus Infecting Onion in Pennsylvania

Iris yellow spot virus (IYSV; genus Tospovirus; family Bunyaviridae) is an economically important pathogen of onion. It is vectored by onion thrips (Thrips tabaci Lindeman) and causes widespread disease of onion in all major onion growing states in the western United States (1). In the eastern United States, IYSV was first reported in Georgia in 2004 (4) and then in New York in 2006 (2). In mid-July of 2010, symptomatic onion (Allium cepa) plants (cv. Candy) were found in New Holland, Pennsylvania, in Lancaster County on a small, diversified commercial farm (40.06°N, 76.06°W). Bleached, elongated lesions with tapered ends occurred on middle-aged leaves on approximately 30% of the 13,760 plants in an area approximately one tenth of an acre. Leaf tissue from five symptomatic plants tested positive for IYSV in a double-antibody sandwich (DAS)-ELISA with IYSV-specific serological reagents from Agdia Inc. (Elkhart, IN). A reverse transcription (RT)-PCR assay was used to verify the presence of IYSV in a subset of symptomatic leaf samples that reacted to IYSV antibodies in DAS-ELISA. Primers specific to the nucleocapsid (N) gene of IYSV (5′-ACTCACCAATGTCTTCAAC-3′ and 5′-GGCTTCCTCTGGTAAGTGC-3′) were used to characterize a 402-bp fragment (3). The resulting amplicons were ligated in TOPO TA cloning vector (Invitrogen, Carlsbad, CA) and two clones of each isolate were sequenced in both directions. Sequence analysis showed a consensus sequence for the partial N gene of the five IYSV isolates from Pennsylvania (GenBank Accession No. JQ952568) and an 87 to 100% nucleotide sequence identity with other IYSV N gene sequences that are available in GenBank. The highest nucleotide sequence identity (100%) was with an IYSV isolate from Texas (GenBank Accession No. DQ658242) and the lowest was with an isolate from India (GenBank Accession No. EU310291). To our knowledge, this is the first report of IYSV infection of onion in Pennsylvania. This finding confirms further spread of the virus within North America. Further study is warranted to determine the impact of IYSV on the Pennsylvania onion industry and to determine viable management strategies, if necessary.

References: (1) D. H. Gent et al. Plant Dis. 88:446, 2004 (2) C. A. Hoepting et al. Plant Dis. 91:327, 2007 (3) C. L. Hsu et al. Plant Dis. 95:735-743. (4) S. W. Mullis et al. Plant Dis. 88: 1285, 2004.