Effects of Thrips Density, Mode of Inoculation, and Plant Age on Tomato Spotted Wilt Virus Transmission in Peanut Plants.

Spotted wilt caused by tomato spotted wilt virus (TSWV; family Bunyaviridae; genus Tospovirus) is a serious disease of peanut (Arachis hypogaea L.) in the southeastern United States. Peanut genotypes with field resistance to TSWV are effective in suppressing spotted wilt. All commercially available genotypes with field resistance to TSWV were developed through conventional breeding. As a part of the breeding process, peanut genotypes are regularly screened under field situations. Despite numerous advantages associated with field screening, it is often limited by inconsistent vector (thrips) and TSWV pressure. A greenhouse transmission protocol would aid in thorough screening of selected genotypes and conserve time. In this study, various parameters associated with TSWV transmission, including tobacco thrips, Frankliniella fusca (Hinds) density, mode of inoculation, and plant age, were evaluated. Greater incidences of TSWV infection were obtained with thrips-mediated inoculation when compared with mechanical inoculation. TSWV inoculation with three, five, and 10 thrips resulted in greater incidences of TSWV infection in plants than inoculation with one thrips. However, incidences of TSWV infection did not vary between plants inoculated with three, five, and 10 viruliferous thrips. With both thrips-mediated and mechanical inoculation methods, incidences of TSWV infection in 1-wk-old plants were greater than in 4-wk-old plants. TSWV copy numbers, as determined by qPCR, also decreased with plant age. Results suggest that using at least three thrips per plant and 1- to 2-wk-old plants would maximize TSWV infection in inoculated plants.