Occurence of Cucumber Mosaic Virus in Ornamental Plants and Perspectives of Transgenic Control

<FONT FACE="Arial">This thesis described the characterization of a range of ornamental-infecting Cucumber mosaic virus strains and the development of novel transgene constructs to improve the efficiency of obtaining resistant transformants which is essential for most ornamental plants that are difficult to transform and regenerate. Nucleotide sequence-based grouping of ornamental-infecting CMV was carried out and found that within the ornamental-infecting CMV viruses both subgroups were represented. Moreover, the analyzed nucleotide sequences of CMV isolates obtained from lily showed remarkably high homology despite different origins. A recombination phenomenon was found in alstroemeria-infecting CMV isolates. This newly discovered event and its beneficial effects on biological fitness have been described. A survey of CMV genome for RNA or protein based transgenic resistance demonstrated that resistance against CMV was feasible. Inverted repeat sequences based on CMV RNA 2 and CP gene have been constructed and transformed into plants. These plants were subsequently tested for high efficiency to obtain resistance. The resistance levels conferred by RNA 2 and CP sequences were greatly improved by using inverted repeat constructs. This efficient approach to obtain CMV resistant transgenic plants opened the way for the use of these transformation constructs for the production of virus resistant ornamental plants