Resistance to alfalfa mosaic virus in transgenic burley tobaccos expressing the AMV coat protein gene

There are no known genetic sources of resistance to alfalfa mosaic virus (AMV) in the genus Nicotiana. In this communication, we describe how we genetically engineered an AMV (strain 425) coat protein (CP) gene into three commercial burley tobacco (N. tabacum L.) genotypes, BY 21, TN 86, and KY 8959, and the evaluation of the transgenic lines in greenhouse and field experiments. In a replicated greenhouse trial, 11 AMV-CP transgenic lines in a BY 21 background were resistant to two AMV isolates, AMV-425 and AMV-KY, but the lines were less resistant to another isolate, AMV-NC. In a 1994 field experiment, we found that nine BY 21 AMV-CP transgenic lines were resistant to AMV-KY when inoculated both before and after transplanting. The level of resistance varied among the nine lines. In 1995, 10 randomly selected AMV-CP lines in each of the three genetic backgrounds were evaluated in a replicated field trial. Mean infection scores of each set of lines were significantly less than those of their non-transgenic counterparts, but there were no significant differences among these three mean infection scores. However, there were significant differences among lines within a genetic background for their response to AMV infection. High sensitivity to AMV infection, found in genotypes TN 86 and KY 8959 that possess an endogenous gene for resistance to potyviruses, was not evident in their AMV-CP transgenic lines. The CP mediated resistance to AMV was effective in reducing viral symptoms in the field and it may provide a valuable source for AMV resistance in tobacco.