Euphorbia pulcherrima. Methods to eliminate poinsettia mosaic virus (PNMV) and reinfection by different methods to reveal the 'nature' of the branching factor

摘要

A survey on the incidence of poinsettia mosaic tymovirus (PnMV) in E. pulcherrima cultivars from Danish growers, as well as imported cultivars, revealed that PnMV was present in all plants tested. PnMV was eliminated by 2 methods, meristem-tip culture of the cultivar Freedom or temp. treatment of Lilo mother plants. The 2 methods for elimination of PnMV in Freedom and Lilo, respectively, resulted in very different plants. Meristem-tip culture gave restricted-branching (r-b) plants with thicker stems and dark, lobed leaves and more intense red bracts when compared with the original Freedom plant. Offspring from the temp. treated Lilo could not be distinguished from the original clone. The plants were repeatedly tested for PnMV. Reinfection of meristem-cultured plants by grafting to the original infected branching plant and by sap-inoculation with PnMV from different sources was carried out. In cuttings from plants which became reinfected branching was recorded. Branching and PnMV were re-established in meristem plants after approach grafting of the 2 possible combinations of virus-free r-b plants to the original PnMV infected branching plant. The branching agent moved up- and downwards from the grafting site. Sap-inoculation with PnMV did not reintroduce branching. These results indicate that the branching was caused by a biological agent, different from PnMV, which has not yet been identified.