First Report of Tomato spotted wilt virus in Soybean (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's 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. References: (1) A. R. Golnaraghi et al. Plant Dis. 88:1069, 2004. (2) R. L. Groves et al. Phytopathology 91:891, 2001. (3) B. S. Kennedy and B. B. Reddick. Soybean Genet. Newsl. 22:197, 1995. (4) H. R. Pappu et al. Tob. Sci. 40:74, 1996.