Engineering resistance against potato virus Y

Potato virus Y is the type species of the potyvirus genus, the largest genus of the plant virus family Potyviridae. The virus causes serious problems in the cultivation of several Solanaceous crops and although certain poly- and monogenic resistances are available, these can not always be employed, e.g. R y genes in potato cv. 'Bintje'. The aim of the research described in this thesis was to establish new forms of resistance against PVY by genetic modification of host plants. One such form of genetic engineered resistance is 'coat protein-mediated resistance', whereby expression of a viral coat protein (CP) in a transgenic plant may confer resistance against infection with the homologous virus, and some closely related viruses.At the start of this investigation no sequence data on the RNA genome of PVY were available, therefore cDNA synthesis and subsequent sequence determination was performed to obtain the necessary PVY CP gene sequence as well as additional sequences from the 3'-terminal region of the viral genome (Chapter 2 and Van der VIugt et al., 1989). This enabled the determination of the exact taxonomic position of the PVY N('tobacco veinal necrosis strain') isolate used in these experiments, among other PVY isolates from at least two different strains. Detailed comparisons of the PVY NCP and 3'-non translated (3'-NTR) sequences with those from a large number of geographically distinct PVY isolates that became available during the course of this investigation, showed that these sequences, in addition to distinguish between different potyvirus species (Ward and Shukla, 1991; Frenkel et al., 1989), can also be used for the distinction between strains of one potyvirus (Chapter 3, Van der VIugt et al., 1992a). Several strain specific amino acid sequences in the CPs and nucleotide sequences in the 3'-NTRs could be discerned, that are possibly involved in virulence and/or symptom expression. Further experiments are required to elucidate the precise biological sig