Inoculation of Tomato Spotted Wilt Virus into Cotton

Tomato spotted wilt virus (TSWV) is an economically important virus of many crops throughout the world. Cotton, Gossypium hirsutum L., has previously been demonstrated to be susceptible to TSWV (1). During the fall of 1996, cotton was assayed as a potential host of TSWV, as it is an important early season host of thrips vectors of TSWV. Four commercial cotton varieties (DP 20, DP 52, DP 5409, and HS 46) were screened for susceptibility to four isolates of TSWV: two from tobacco, one from pineapple, and one from dahlia. Greenhouse-grown plants in the first true leaf stage were inoculated mechanically. Mean percent infection ranged from 20 to 33% (x = 27%) across all cotton varieties screened against all virus isolates 21 days post-inoculation. TSWV was recovered through mechanical inoculation from double antibody sandwich-enzyme-linked immunosorbent assay (DAS ELISA) positive cotton leaves in 83% of indicator plants, Emilia sonchifolia (L.) DC. ex Wight. Individual cotton plants testing TSWV ELISA positive were held for an additional 28 days with 4% of these again testing virus positive. The four cotton varieties were tested in the cotyledon, one-leaf, and four-leaf stages for susceptibility to tobacco thrips, Frankliniella fusca Hinds, transmission of one TSWV isolate from tobacco. First instar thrips were obtained from an avirulent colony. Mean percent infection among all varieties assayed was 10, 63, and 5%, respectively, for the three developmental stages. Cotton appears to be most susceptible in the one-leaf developmental stage with potential to serve as a source for TSWV spread to other crops. Reference: (1) G. L. Schuster and R. S. Haliwell. Plant Dis. 78:100, 1994.