Department of Plant Pathology, University of Georgia, Tifton 31793
Crop Protection and Management Research Unit, USDA-ARS, Tifton, GA 31793
Impatiens necrotic spot virus (INSV), family Bunyaviridae, genus Tospovirus, is an emerging virus found mostly in ornamentals under greenhouse production. INSV has been detected in peanut (Arachis hypogaea L.) in Georgia and Texas (3) and recently in tobacco (Nicotiana tabacum L.) in the southeastern United States (2) but little is known about INSV distribution and impact on these crops. Noncrop plant hosts are likely to contribute to disease spread by serving as reservoirs for the virus and reproductive hosts for thrips (Frankliniella occidentalis Pergande), which transmit the virus. Yellow nutsedge, a native of North America, and purple nutsedge introduced from Eurasia, are considered serious weed problems in the southeastern United States. To date, there are no reports of natural INSV infections in these weeds. A survey was conducted at two research farms in Tift County, Georgia to determine if yellow and purple nutsedge plants were naturally infected with Tomato spotted wilt virus (TSWV) and INSV. The first field at the Black Shank Farm had been planted with flue-cured tobacco K-326 earlier in the year and fallow at the time of sampling. The second field at the Ponder Farm was planted at the time of sampling with yellow squash (Cucurbita pepo L.) and cabbage (Brassica oleracea L.). In early October 2002, 90 nutsedge plants were taken at random from each site. Leaf and root tissues of each of the nutsedge plants were tested for TSWV and INSV using double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) alkaline phosphatase antisera kits (Agdia Inc., Elkhart, IN). No visible symptoms of INSV or TSWV were observed. Samples from the field at the Black Shank Farm resulted in 2 of 26 positive for INSV in purple nutsedge plants and 6 of 64 in yellow nutsedge plants. At the Ponder Farm, 3 of 12 were positive for INSV in purple nutsedge plants and 14 of 78 in yellow nutsedge plants. None of the samples in either site tested positive for TSWV. The DAS-ELISA positive samples were verified for INSV using reverse transcription-polymerase chain reaction (RT-PCR) as previously described by Dewey et al. (1). Total RNA extracts were obtained from the DAS-ELISA positive nutsedge samples using RNeasy extraction kits (Qiagen Inc., Valencia, CA). The RT-PCR was carried out with primer 1F: 5′-TCAAG(C/T) CTTC(G/T)GAA(A/G)GTGAT 3′ (1) and primer 2R: 5′-ATGAACAAAGCAAAGATTACC 3′ specific to the 3′ end of the INSV N gene open reading frame (GenBank Accession No. NC003624). DAS-ELISA negative tissues of Cyperus esculentus L. and Emilia sonchifolia (L.) DC and an E. sonchifolia DAS-ELISA positive for INSV were included in the reactions as controls. All of the DAS-ELISA positive nutsedge samples yielded an amplification product with the expected size of 298 bp when PCR products were resolved by agarose (0.7%) gel electrophoresis. The relatively high occurrence of INSV found in the sampled fields may explain the recent increase in incidence of INSV in susceptible field crops. Although yellow nutsedge is more common than purple nutsedge in North America, the potential for dispersal of INSV in both species could be significant because of the nature of nutsedge tuber survival and spreading capabilities.
References: (1) R. A. Dewey et al. J. Virol. Methods 56:19, 1996. (2) N. Martínez-Ochoa et al. On-line publication. doi:10.1094/PHP-2003-0417-01-HN. Plant Health Progress, 2003. (3) S. S. Pappu et al. Plant Dis. 83:966,1999.