Response of Peanut, Pepper, Tobacco, and Tomato Cultivars to Two Biologically Distinct Isolates of Tomato spotted wilt virus

Spotted wilt disease, caused by Tomato spotted wilt virus (TSWV), is an economically important disease in peanut, pepper, tobacco, and tomato in the southeastern United States. However, very little is known about the biological variability existent in the virus population. Fourteen isolates of TSWV collected in Georgia were evaluated for symptom severity. The majority of the isolates produced severe systemic necrosis. One mild (GATb-1) and one severe (GAL) isolate were further examined because of the distinct differences in their virulence and symptomatology on tobacco. GATb-1 caused a few chlorotic spots and mild systemic symptoms, whereas GAL produced a large number of local lesions and severe systemic necrosis. Distinct differences in the response of selected commercial cultivars of peanut, tobacco, and tomato to GATb-1 and GAL infection were observed. GAL was lethal to a widely grown tobacco cultivar, K326. Georgia Green, a field resistant peanut cultivar, and C11-2-39, a breeding line with the highest level of known resistance to TSWV, were more susceptible to GAL than to GATb-1. BHN 444, a newly released TSWV-resistant tomato cultivar, showed a resistant reaction, whereas Stiletto, a newly released TSWV-resistant pepper cultivar, was susceptible to both GATb-1 and GAL isolates. Information on the biological diversity of TSWV may be useful in developing more durable TSWV-resistant crops

First report of Tomato spotted wilt virus insoybean (Glycine max) in Georgia

Tomato spotted wilt virus (TSWV) is a member of the family Bunyaviridae and has a wide host range including important crops such as tomato, pepper, tobacco, peanut, and onion. In areas of Georgia, soybean (Glycine max) is double cropped between two onion crops and as a rotation crop with peanuts. Soybeans do not show any TSWV symptoms, and therefore, have not been tested on a large scale for the virus. However, because symptomless weed and crop plants provide a reservoir for TSWV and the thrips vectors (2), a survey was conducted during the summer of 2005 to evaluate the occurrence of TSWV in soybean. The survey took place in seven counties in southern Georgia with field sizes ranging between 0.4 and 20 ha (1 and 50 acres). Soybean cultivars included Haskell, DP7220, DP6770, Pioneer 97B52, and Vigoro V622NRR. Of 848 randomly selected plants tested using the double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) (Agdia, Inc., Elkhart, IN), 6.6% tested positive for TSWV. Plants testing positive ranged from seedling to the pod-setting stages. Leaves and roots of several plants tested positive, indicating a systemic infection. Soybean plants testing positive using ELISA were blotted onto FTA cards (Whatman Inc., Brentford, UK) to bind viral RNA for preservation, and the blotted samples were processed according to the manufacturer\u27s protocol. Reverse transcription-polymerase chain reaction using punch-outs from the FTA cards and TSWV nucleocapsid gene specific forward and reverse primers (5′-TTAAGCAAGTTCTGTGAG-3′ and 5′-ATGTCTAAGGTTAAGCTC-3′), respectively (4), confirmed the identity of TSWV. TSWV has been found in soybean in other parts of the world (1) but has only been reported in the United States in a survey from Tennessee (3). To our knowledge, this is the first report of the occurrence of TSWV in soybean in Georgia. The role soybean plays as a reservoir or green bridge for thrips and TSWV is currently unknown

Firstreport of Iris yellow spot virus in spiny sowthistle (Sonchus asper) in the United States

Iris yellow spot virus (IYSV) is a member of the genus Tospovirus in the family Bunyaviridae. Its known host range is very limited, and the currently known hosts include onion, leek, lisianthus, and alstroemeria (2). The virus is vectored by onion thrips (Thrips tabaci). Onion (Allium cepa) is grown as a winter crop in Georgia from September to April and is the only known host commercially grown in the region. However, the virus has been found across the onion-growing region in the state every year since its first occurrence during 2003 (3). Consequently, the virus must oversummer in other host(s) or its insect vector. Accordingly, samples of weeds were collected in the vicinity of onion fields and cull piles in the Vidalia region and tested for the presence of IYSV by a double-antibody sandwich (DAS)-ELISA (Agdia, Inc., Elkhart, IN). One of three nonsymptomatic spiny sowthistle samples tested positive by ELISA for IYSV. Total RNA was extracted from the leaf using the RNeasy Plant Mini Kit (Qiagen, Valencia, CA) following the manufacturer\u27s protocol. Two microliters were used for reverse transcription (RT)-PCR with the forward primer (5′-TCAGAAATCGAGAAACTT-3′) and reverse primer (5′-TAATTATATCTATCTTTCTTGG-3′) for the IYSV nucleocapsid gene (1). A band of the expected size (approximately 800 bp) was obtained and sequenced. The sequence from the sowthistle (GenBank Accession No. EU078327) matched IYSV sequences from Georgia and Peru in a BLAST search in GenBank (closest matches with Accession Nos. DQ838584, DQ838592, DQ838593, and DQ658242). This is to our knowledge, the first confirmed report of IYSV infecting spiny sowthistle. The distribution of IYSV in sowthistle and its role as an oversummering host for IYSV is currently an on-going study

Effect of transplant age,tobacco cultivar, acibenzolar-S-methyl and imidacloprid on tomato spotted wilt infection in fluecuredtobacco

Tomato spotted wilt virus (TSWV) has become the most serious problem in flue-cured tobacco in Georgia and is a growing problem in other tobacco-growing areas in the United States. The effects of transplant age (6 to 10 weeks), tobacco cultivar (K-326 and NC-71), and preplant applications of acibenzolar-S-methyl (ASM) and the insecticide imidacloprid (IMD) were evaluated on levels of TSWV infection, number of symptomatic plants, and yield in field trials over 4 years. In all 4 years and in four of five trials, treatment of transplants with ASM and IMD resulted in fewer symptomatic plants, smaller areas under the disease progress curve (AUDPC), and higher yields compared with the nontreated controls. There were no consistent effects of transplant age or cultivar on number of symptomatic plants or systemic infections, AUDPC, or yield. Treatment of transplants with ASM and IMD can significantly reduce the number of symptomatic plants in the field and substantially increase yields and value per hectare

First report of Tomatospotted wilt virus in leek (Allium porrum) in the United States

omato spotted wilt virus (TSWV) is a member of the family Bunyaviridae. It has many important crop hosts including tomato, pepper, tobacco, peanut, and onion. In Georgia, Vidalia onions (Allium cepa), a close relative of leek, can be infected by TSWV and Iris yellow spot virus (IYSV), which is another thrips-vectored tospovirus (2). For this reason, samples of leek transplants with virus-like symptoms in one field at the border of Georgia and Florida were tested for the presence of TSWV and IYSV. The transplants had been grown from seed in a greenhouse at the same location. The sampled plants exhibited extended bleaching of leaf tips and necrotic lesions. These symptoms were also seen on onion plants infected with TSWV and IYSV. The only natural infections of leek with IYSV have been reported thus far only from Reunion Island (4) and Slovenia (1), but to our knowledge, TSWV has not been reported as a pathogen of leek. Green tissue near the necrotic lesions and bleached tips of one symptomatic leaf per plant was sampled and analyzed using a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) (Agdia, Inc., Elkhart, IN). Of 90 plants tested, eight were positive for TSWV and none were positive for IYSV. Leek samples testing positive using ELISA were blotted onto FTA cards (Whatman Inc., Brentford, UK) to bind viral RNA for preservation and then processed according to the manufacturer\u27s protocol. Punch-outs from the FTA cards were used for reverse transcription polymerase chain reaction (RT-PCR) with the TSWV-specific forward primer (5′-TTAAGCAAGTTCTGTGAG-3′) and reverse primer (5′-ATGTCTAAGGTTAAGCTC-3′) (3) to confirm the identity of TSWV. The primers are specific to the viral nucleocapsid gene. An amplicon of the expected size (774 bp) was produced from TSWV ELISA-positive leek plants, but not from healthy controls. TSWV has been found in many plants worldwide, but to our knowledge this is the first report of TSWV infecting leek. The effect that TSWV has on leek production is currently unknown