Incidence of Soybean dwarf virus and Identification of Potential Vectors in Illinois Barbara Harrison and Todd A. Steinlage, Department of Crop Sciences, University of Illinois, Urbana 61801; Leslie L. Domier, USDA-ARS, Department of Crop Sciences, University of Illinois, Urbana 61801; and Cleora J. D’Arcy, Department of Crop Sciences, University of Illinois, Urbana 61801 has been used to further subdivide the ABSTRACT dwarfing and yellowing strains (32). Harrison, B., Steinlage, T. A., Domier, L. L., and D’Arcy, C. J. 2005. Incidence of Soybean SbDV-DS strains are transmitted by A. dwarf virus and identification of potential vectors in Illinois. Plant Dis. 89:28-32. solani, and SbDV-DP strains are transmit- ted by Acyrthosiphon pisum (Harris) and Soybean dwarf virus (SbDV), which causes an important disease of soybeans in Japan, is persis- Nearctaphis bakeri (Cowen). Similarly, tently transmitted by aphids and is endemic in forage legumes in the United States. To determine SbDV-YS strains are transmitted by A. the incidence of SbDV in Illinois, we collected clovers and forage legumes in a total of 49 Illi- solani, and SbDV-YP strains are transmit- nois counties in 2001 and 2002 and tested them for the presence of SbDV by reverse- ted by Acyrthosiphon pisum, N. bakeri, transcription–polymerase chain reaction. SbDV was detected in 43% of red clover (Trifolium pratense), 10% of white clover (T. repens), and 3% of yellow sweet clover (Melilotus officinalis) and very rarely by Aphis glycines Matsu- plant samples. The dwarfing strain (SbDV-D) was the predominant strain detected in Illinois. In mura (16). SbDV isolates from different 2000, Aphis glycines, an aphid species that colonizes soybeans, was reported for the first time in geographic regions also can display differ- North America. To determine whether A. glycines or aphid species found colonizing clover were ent transmission specificities. Japanese vectors of SbDV, transmission studies were conducted. Aphids of the species Nearctaphis bakeri SbDV isolates were transmitted by A. so- reproducibly vectored SbDV among red clovers, and from red clover to soybean. A. glycines did lani, Acyrthosiphon pisum, and N. bakeri, not transmit SbDV; neither did two other clover-infesting aphid species, Acyrthosiphon pisum but not by Myzus persicae (Sulzer) or and Therioaphis trifolii. Aphis craccivora Koch (16,26). In New Zealand and Tasmania, Acyrthosiphon pisum, Aulacorthum solani, and Macrosi- phum euphorbiae (Thomas) vectored Soybean dwarf virus (SbDV), a member In Japan, the polyphagous Aulacorthum white-clover infecting isolates of SbDV, of the Luteoviridae, was first identified in solani (Kaltenbach) is the principal vector but as in Japan, M. persicae and Aphis association with outbreaks of dwarfed of SbDV (15). In northern Japan, A. solani craccivora did not transmit SbDV (19). In soybean (Glycine max L.) plants that had is holocyclic, and its eggs overwinter on the United States, SbDV isolates from severe yield losses in northern Japan in red clover (Trifolium pratense L.) and white clover were transmitted by both 1969 (29). Subsequently, similar viruses white clover (T. repens L.) plants, many of Acyrthosiphon pisum and M. persicae, but were identified in Australia, Ethiopia, Iran, which are infected with SbDV (2,15). In not by Aulacorthum solani (9,12,19). New Zealand, Syria, and the United States the spring, viruliferous winged aphids This specificity of transmission is en- (1,20,22–25,33). In northern regions of develop on these hosts and fly to soybean, gendered by interactions between aphid Japan, SbDV is one of the most important where feeding of viruliferous aphids leads membrane barriers and virus proteins. virus diseases of soybean (15). Yield losses to SbDV infections. The disease is spread Gildow et al. (12) examined the movement from SbDV have been shown to be linearly in the field by parthenogenic apterous of transmissible and nontransmissible correlated with percent SbDV infection in aphids throughout the summer, until sexual SbDV isolates through M. persicae and soybean fields, with a 50% infection caus- generations emerge again in autumn and observed that a nontransmissible SbDV ing a 40% yield loss that results from a migrate back to clover to lay eggs and isolate could not penetrate the salivary reduced number of pods set (2,28). Due to complete their life cycle (2,15). basal lamina of M. persicae. The salivary the persistent nature of its transmission, Many species from several plant fami- basal plasmalemma, the cell layer adjacent SbDV is transmitted efficiently only by lies are susceptible to SbDV, but the most to the basal lamina, served as the barrier colonizing aphids (26). In the United common hosts of SbDV are members of for transmission for an isolate that was not States, SbDV has been detected primarily the Fabaceae (4,8,30). Based on the symp- transmitted by A. solani. SbDV-D and in clover plants and rarely infects soybean, toms they produce in soybean, SbDV iso- SbDV-Y strains share 83% amino acid presumably because of the absence of lates have been divided into two strains: sequence identity (32). The greatest se- aphid vectors that colonize soybean (9,10). dwarfing (SbDV-D) and yellowing (SbDV- quence variability between the two strains Y) (27). SbDV-D symptoms in soybean of SbDV is found in the C-terminal half of plants include shortened internodes and the coat protein readthrough domain and Corresponding author: L. L. Domier petioles and dark colored, brittle leaves the 3′ noncoding region (32). Yet amino E-mail: [email protected] that curl downward. SbDV-Y causes less acid sequence variation in the N-terminal Mention of a trademark, proprietary product, or stunting, but the symptoms tend to be more region of the readthrough domain has been vendor does not constitute a guarantee or warranty severe and include interveinal chlorosis, reported to be related to specificity of of the product by the USDA or the University of thickened and brittle mature leaves, and aphid transmission of SbDV (31). Illinois and does not imply its approval to the leaflets that do not fully develop and be- Aphis glycines was identified in the exclusion of other products or vendors that may come rugose (30). Dwarfing and yellowing United States for the first time in 2000 (13) also be suitable. strains of SbDV show differences in host and subsequently has spread throughout Accepted for publication 26 July 2004. range. Dwarfing strains infect red clover much of the soybean growing region of but not white clover, while yellowing North America (17). The introduction of A. strains infect white clover but not red clo- glycines, an aphid species that colonizes DOI: 10.1094/PD-89-0028 ver (8,26). soybean plants, has the potential to in- This article is in the public domain and not copy- Like other members of the Luteoviridae, rightable. It may be freely reprinted with custom- crease the incidence in North America of ary crediting of the source. The American Phyto- SbDV isolates can show differential trans- persistently and nonpersistently transmit- pathological Society, 2005. mission by different aphid species, which ted viruses in soybean. A. glycines has 28 Plant Disease / Vol. 89 No. 1 been reported to transmit several viruses, Fig. 1) was synthesized that flanked a re- the Illinois Natural History Survey. To including Alfalfa mosaic virus, Bean com- gion in the 3′ NCR that was diagnostically clean the field-collected aphids of persis- mon mosaic virus, Bean yellow mosaic variable between dwarfing and yellowing tently transmitted viruses, they were virus, Cucumber mosaic virus, Indonesian strains. RT-PCR reactions were performed placed on greenhouse-grown healthy red soybean dwarf virus (ISDV), Peanut stripe as above with an annealing temperature of clover leaves and new-borne nymphs were virus, Peanut stunt virus, Soybean mosaic 55°C. immediately transferred to leaves of virus (SMV), and Tobacco ringspot virus Incidence of SbDV infection. Clover healthy plants. Aphis craccivora was (3,7,14,18). ISDV is another member of and other plants were collected from reared on healthy Vicia faba L. cv. Im- the Luteoviridae that causes symptoms ditches and field borders during the grow- proved Long Pod. Aphis glycines was similar to SbDV in soybean but is sero- ing seasons of 2001 and 2002 from an reared on healthy soybean cv. Williams 82. logically distinct from SbDV (18). While average of two locations per county. In Acyrthosiphon pisum, N. bakeri, and T. in one instance A. glycines was reported to 2001, entire plants were dug up from 35 trifolii were reared on healthy red clover. transmit SbDV rarely (15), other reports counties, brought back to the greenhouse, All colonies were maintained in cylindrical have found no transmission of Japanese and replanted in pots. Plants that tested acrylic cages in growth chambers main- isolates of SbDV by A. glycines (28,29). positive for SbDV by RT-PCR were used tained at 23°C and 17-h day length. This is the first study of SbDV in Illi- as sources of inoculum for transmission Transmission of SbDV by aphids. nois. Our objectives were to determine the studies described below. In 2002, leaf tis- SbDV-D isolates were used for transmis- distribution of SbDV in Illinois in forage sue from clover plants was collected from sion studies because they were the most legumes that border soybean fields, deter- an average of two locations in 36 Illinois prevalent in Illinois. Five SbDV-positive mine the prevalent strain(s) of the virus, counties. All plants were analyzed for clover samples, two from Champaign and identify potential vectors of the virus SbDV infection using RT-PCR. In 2001, a County and one each from Coles, Cumber- in Illinois. subset of plants negative for SbDV infec- land, and Douglas counties in Illinois, tion with primers SbDV-3248F and SbDV- were used as source tissue in initial aphid MATERIALS AND METHODS 3529R were retested by RT-PCR using transmission tests for SbDV-D.