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© 2003 Plant Management Network.
Accepted for publication 14 March 2003. Published 17 April 2003.


First Report on the Incidence of Mixed Infections of Impatiens necrotic spot virus (INSV) and Tomato spotted wilt virus (TSWV) in Tobacco Grown in Georgia, South Carolina, and Virginia


N. Martínez-Ochoa and A. S. Csinos, Department of Plant Pathology, The University of Georgia, Coastal Plain Experiment Station, Tifton GA 31793-0748; E. B. Whitty, Agronomy Department CES/IFAS, University of Florida, Gainesville FL 32611; A. W. Johnson, Department of Entomology, Pee Dee Research & Education Center, Clemson University, Florence SC 29506-9706; and M. J. Parrish, Virginia Cooperative Extension, Dinwiddie County, Dinwiddie VA 23841


Corresponding author: N. Martínez-Ochoa. nmartinez@tifton.uga.edu


Martínez-Ochoa, N., Csinos, A. S., Whitty, E. B., Johnson, A. W., and Parrish, M. J. 2003. First report on the incidence of mixed infections of Impatiens necrotic spot virus (INSV) and Tomato spotted wilt virus (TSWV) in tobacco grown in Georgia, South Carolina, and Virginia. Online. Plant Health Progress doi:10.1094/PHP-2003-0417-01-HN.


Fig. 1. Typical systemic spotted wilt symptoms in K326 tobacco 45 days after transplanting (Bowen Farm, Tift County, Georgia).


 

Tomato spotted wilt caused by Tomato spotted wilt virus (TSWV) continues to be a serious disease problem on tobacco (Nicotiana tabacum L.) (Fig. 1), peanut (Arachis hypogaea L.), tomato (Lycopersicon esculentum Mill.), and pepper (Capsicum annum L.) in the southeastern United States (2). Impatiens necrotic spot virus (INSV, formerly known as TSWV-I) is an emerging virus found mostly in greenhouse production of ornamentals and is also vectored by thrips (1). A few years ago INSV was detected in peanut in Georgia and Texas (3) and its occurrence appears to be increasing (4). Mixed infections of TSWV and INSV in tobacco have been observed within the last two years in North Carolina and Kentucky (J. W. Moyer and W. Nesmith, personal communications). Our objective was to sample several locations in Georgia, Florida, South Carolina and Virginia to confirm and report the presence of natural TSWV and INSV mixed infections in tobacco.

A total of six counties located in Georgia (Tift County: K326 number of samples tested [n] = 33, NC71 n = 300), Florida (Columbia County: K326 n = 90; Suwannee County: NC72 n = 90), South Carolina (Williamsburg County: JA732 n = 60, JA858 n = 15, NC2326 n = 15; Darlington County: tobacco cv. Xanthi n = 52, JA732 n = 9) and Virginia (Dinwiddie County: NC71 n = 100, NC72 n = 50) were sampled at different times during 2002. Tobacco tissues used for virus testing consisted mostly of roots from mature plants collected between mid-July and late August, except for one mid-May sampling (45 days after transplanting) in Georgia and an early October sampling in South Carolina, where leaves were used. Tissues were tested by DAS-ELISA with commercial antisera for each virus (Agdia Inc., Elkhart, IN).

Several asymptomatic samples (ranging from 8 to 34%, depending on the site) tested positive for TSWV, confirming previous observations of virus infections not expressing typical Tomato spotted wilt symptoms (2). The occurrence of mixed infections of TSWV and INSV was confirmed in Georgia (K326 = 30%), South Carolina (JA732 = 8.33%, JA858 = 40%, NC2326 = 6.66%, Xanthi = 11.54%) and Virginia (NC72 = 22%, NC71 = 1%). Only single TSWV infections were detected for both locations in Florida, one site in Virginia (NC71 = 24%), and one site in Georgia (NC71 = 58%). Single TSWV infections were detected in all other fields sampled with an incidence ranging from 16 to 94%. Single INSV infections were not detected in any of the tobacco samples tested in the four states.

Preliminary data suggests that in many instances where INSV tested positive, most plants also had high ELISA titers of TSWV, indicating that the expression of some severe symptoms could be the result of mixed infections (Fig. 2) and INSV might be acting as a helper virus. There are single infections of INSV present in weeds around tobacco fields (unpublished data) and we presume they are present in tobacco as well but currently at very low levels. Perhaps INSV development in the thrips vectors or the susceptible hosts depends on the presence of prior infections with TSWV. Presently there is not enough information to understand the significance of TSWV-INSV dual infections and our efforts are focusing towards future research on their individual and simultaneous transmission by thrips.


 

Fig. 2. K326 tobacco field trial (eight middle rows) with 94% incidence of spotted wilt and 30% average occurrence of mixed infections with TSWV and INSV (Bowen Farm, Tift County, Georgia).

 

Literature Cited

1. Daughtrey, M. L., Jones, R. K., Moyer, J. W., Daub, M. E., and Baker, J. R. 1997. Tospoviruses strike the greenhouse industry: INSV has become a major pathogen on flower crops. Plant Dis. 81:1220-1230.

2. Pappu, H. R., Csinos, A. S., McPherson, R. M., Jones, D. C., and Stephenson, M. G. 2000. Effect of acibenzolar-S-methyl and imidacloprid on suppression of tomato spotted wilt Tospovirus in flue-cured tobacco. Crop Prot. 19:349-354.

3. Pappu, S. S., Black, M. C., Pappu, H. R., Brenneman, T. B., Culbreath, A. K., and Todd, J. W. 1999. First report of natural infection of peanut (Arachis hypogaea) by Impatiens necrotic spot tospovirus (Family Bunyaviridae). Plant Dis. 83:966.

4. Wells, M. L., Pappu, H. R., Culbreath, A. K., Todd, J. W., and Brown, S. L. 2001. Field survey of Impatiens necrotic spot virus in Georgia peanut. Peanut Sci. 28:34-37.