Natural Infection of Iris yellow spot virus in Twoscale Saltbush (Atriplex micrantha) Growing in Utah

Abstract

Iris yellow spot virus (IYSV; family Bunyaviridae, genus Tospovirus) continues to be an economically important pathogen affecting onion bulb and seed production in several parts of the world and the United States (1). Several weeds were reported naturally infected with IYSV (1,2,4). Leaves of Atriplex micrantha Ledeb. (synonym A. heterosperma Bunge) were collected from naturally occurring plants in a weed trial conducted in commercial onions grown in Box Elder County, UT on 24 September 2008. Leaves displayed a range of symptoms including spotting, chlorosis, and necrosis. Symptomatic leaves were preferentially selected for subsequent diagnostic analyses. Samples were positive for IYSV when tested by double-antibody sandwich-ELISA using a commercially available kit (Agdia Inc., Elkhart, IN). For further confirmation, total nucleic acid extracts from the symptomatic parts of the leaves were prepared and tested for the presence of IYSV by reverse transcription-PCR with primers specific to the nucleocapsid (N) gene coded by the small (S)-RNA of IYSV. The forward and reverse primer pair, 5′-TCAGAAATCGAGAAACTT-3′ and 5′-CACCAATGTCTTCAACAATCTT-3′, respectively, amplifies a 751-nt fragment of the N gene (3). An amplicon of expected size was obtained, cloned, and sequenced. The nucleotide sequence analysis and comparison with known IYSV S-RNA sequences showed that the sequence of the amplicon from A. micrantha (GenBank Accession No. FJ493541) shared more than 84% nt sequence identity with the corresponding region of IYSV isolates available in GenBank, confirming the IYSV infection of the new host weed. The highest sequence identity (98%) was with an IYSV isolate from Jefferson County, OR (GenBank Accession No. DQ233479). To our knowledge, this is the first report of IYSV infection of A. micrantha under natural conditions. The role of A. micrantha and other weeds in IYSV epidemiology needs further investigation. References: (1) D. Gent et al. Plant Dis. 90:1468, 2006. (2) C. Nischwitz et al. Plant Dis. 91:1518, 2007. (3) H. R. Pappu et al. Arch. Virol. 151:1015, 2006. (4) R. Sampangi et al. Plant Dis. 91:1683, 2007.