Interactions of sugar-beet curly top virus and an unusual mutant

Abstract

A virus that produces marked vein yellowing was found in a Turkish to-bacco plant that had recovered from curly top. This virus is designated “yellow-vein virus” to differentiate it from typical curly top virus. Insofar as tested, it has the same host range as curly top virus except that it did not persist in Nicotiana glauca Graham, a host of the curly top virus. The yellow-vein virus was transmitted by the beet leafhopper, Circulifer tenellus (Baker), by four species of Cuscuta, and by graftage. It was not transmitted by juice inoculation or through seeds. The yellow-vein virus has not been separated from typical curly top virus but the two have been transmitted in combination to tobacco, sugar beet, tomato, and other plants. No symptoms were produced by the yellow-vein virus on sugar beet but the virus was recovered from inoculated plants. The presence of the yellow-vein virus apparently results in a marked decrease in the curly top component in tobacco. Concentrations of the two components appear to vary greatly in different plants. If the yellowing component is dominant in tobacco, the plants are yellow and stunted; if the curly top component is dominant, leaves are green, curled, and dwarfed at first, but the plants recover. If the two components are more or less evenly balanced, usually little injury results. When tomato plants were inoculated by means of the beet leafhopper, those infected with curly top virus alone almost invariably died, whereas those infected with both yellow-vein and curly top viruses usually showed symptoms of only moderate severity and soon recovered. Tobacco plants that recovered from curly top appeared to be immune to infection with yellow-vein virus introduced by means of the beet leaf-hopper. They were resistant, but not immune, to infection with yellow-vein virus from diseased scions. Typical vein yellowing was produced on Nicotiana glauca Graham, immune to infection by yellow-vein virus, and Datura meteloides DC., immune to both curly top and yellow-vein viruses, when infected Turkish tobacco scions were in a position to supply carbohydrates and virus to plants of these two species. The virus was lost by the plants of both species in a few days after the tobacco scions were removed. The yellow-vein virus seems to be closely limited to the phloem, and rapid movement appears to be correlated with the transport of carbohydrates. Evidence indicates strongly that the vein-yellowing virus is a strain of curly top virus that probably arose as a mutant in a curly top-infected tobacco plant.