High Incidence of Tobacco Streak Virus in Tobacco and Its Transmission byMicrocephalothrips abdominalisand Pollen fromAgeratum houstonianum

Incidence of tobacco streak virus (TSV) in an Australian tobacco crop at flowering was shown by enzyme-linked immunosorbent assay (ELISA) to be 58−59% in outside rows near weeds infected with TSV, decreasing to 10−18% in the 12th row inside the crop. The most prevalent dicotyledonous weed, Ageratum houstonianum, had a 50% incidence of infection and its flower heads were commonly infested with Microcephalotrips abdominalis. In transmission tests with either five or 10 adult thrips and pollen taken from the nearby A. houstonianum, TSV infection occurred in 32 of 45 tobacco, 11 of 12 cucumber, two of 12 Nicotiana clevelandii, and 18 of 22 Chenopodium amaranticolor test seedlings (.)